Picture 1 – Cable ladder system
UPDATE March 15, 2011: This blog is now being re-constructed. Please read the re-opening post here, Blog Re-construction.
Copyright http://electricalinstallationblog.blogspot.com/ - Electrical cable ladder pictures
Wednesday, January 13, 2010
Electrical cable ladder pictures
Below is a picture of cable ladder installation. I only have time for this picture today, but you will be able to see more installation pictures of this component of electrical installations soon. However, you can see more pictures of electrical installations in my other posts on this blog by visiting this anchor post, Free electric installation pictures. You can also see cable tray pictures at this post, Cable trays and ladder installation.
Picture 1 – Cable ladder system
UPDATE March 15, 2011: This blog is now being re-constructed. Please read the re-opening post here, Blog Re-construction.
Copyright http://electricalinstallationblog.blogspot.com/ - Electrical cable ladder pictures
Picture 1 – Cable ladder system
UPDATE March 15, 2011: This blog is now being re-constructed. Please read the re-opening post here, Blog Re-construction.
Copyright http://electricalinstallationblog.blogspot.com/ - Electrical cable ladder pictures
Sunday, January 10, 2010
Emergency light installation pics
I have uploaded few pictures showing the method of installing a ceiling-recessed emergency lighting (EL) unit. This work was photographs at a high-rise building construction a few months ago.
As far as the choice of types of the EL light, I would personally prefer a surface mounted self-contained type. The one being installed in this picture is also a battery-backed self-contain type, but it is recessed mounted.
Being a technical guy, the surface mounted type of emergency lighting gives a certain feeling of comfort in my opinion. That is because you can see the whole unit right at the surface of the ceiling. As this lighting is intended for emergency (the failure of the mains supply can also be considered an form of emergency in my view because no high-rise building can operate without the mains supply. So, the standby electrical generator is an emergency supply and this low powered light fitting is an emergency lighting), it does not light up normally. It will only turn on when there is an emergency (when the power fails)
Being rarely in operation, it is rarely noticed if the unit is no longer functional or not working. Or if it has been damaged or vandalized.
So being surface mounted gives a feeling that you will more likely notice if something goes wrong with the emergency light.
The original design for this building was originally surface mounted units. However, during the construction stage, some visiting architect commented that the light fittings have spoiled the beauty of the interior of the open office space and the emergency lighting should be using a concealed type.
Therefore, we changed this emergency light to the concealed one for the office and lift lobby areas. However, the rest of the building was still using the surface mounted types.
Below are a few of the photographs that I took. However, if your interest is just on electrical pictures, just go straight to this post, Free electric installation pictures. There you can see pictures from other posts, which may be difficult for you to dig out as they are scattered all over this blog.
Picture 1 – The emergency lighting unit at its final position
Picture 2 – A closer look of the mounting of the unit
Picture 3 – A side view to show how the EL light fits in to the ceiling panel
Picture 4 – A top view (above the ceiling panel) showing how the unit is fixed to the ceiling board
Picture 5 – Another rear view of the emergency light unit
Copyright http://electricalinstallationblog.blogspot.com/ Emergency light installation pics
As far as the choice of types of the EL light, I would personally prefer a surface mounted self-contained type. The one being installed in this picture is also a battery-backed self-contain type, but it is recessed mounted.
Being a technical guy, the surface mounted type of emergency lighting gives a certain feeling of comfort in my opinion. That is because you can see the whole unit right at the surface of the ceiling. As this lighting is intended for emergency (the failure of the mains supply can also be considered an form of emergency in my view because no high-rise building can operate without the mains supply. So, the standby electrical generator is an emergency supply and this low powered light fitting is an emergency lighting), it does not light up normally. It will only turn on when there is an emergency (when the power fails)
Being rarely in operation, it is rarely noticed if the unit is no longer functional or not working. Or if it has been damaged or vandalized.
So being surface mounted gives a feeling that you will more likely notice if something goes wrong with the emergency light.
The original design for this building was originally surface mounted units. However, during the construction stage, some visiting architect commented that the light fittings have spoiled the beauty of the interior of the open office space and the emergency lighting should be using a concealed type.
Therefore, we changed this emergency light to the concealed one for the office and lift lobby areas. However, the rest of the building was still using the surface mounted types.
Below are a few of the photographs that I took. However, if your interest is just on electrical pictures, just go straight to this post, Free electric installation pictures. There you can see pictures from other posts, which may be difficult for you to dig out as they are scattered all over this blog.
Picture 1 – The emergency lighting unit at its final position
Picture 2 – A closer look of the mounting of the unit
Picture 3 – A side view to show how the EL light fits in to the ceiling panel
Picture 4 – A top view (above the ceiling panel) showing how the unit is fixed to the ceiling board
Picture 5 – Another rear view of the emergency light unit
Copyright http://electricalinstallationblog.blogspot.com/ Emergency light installation pics
Thursday, January 7, 2010
Free electric installation pictures
I thought the word free pictures in the post title would attract a few extra visitors to this electrical installation blog. We will see whether it works or not.
Photo 1 - Electrical services inside a building
Jokes aside, actually I received a few emails from some friends in the education business (i.e. local universities) complaining that they like the real construction pictures and the temporary electrical installation pictures that I uploaded to this blog (visit the anchor post here, Temporary Electrical Installations).
However, the pictures are scattered all over the place. A few of them suggested that I put these pictures into one post and the same for the electrical schematics.
I know these people wanted to use these photos and electrical diagrams for their teaching works. Part of me feels the reluctance to this step because I know these real construction photos have some monetary values.
If I locate them at one place, then many readers who are hunting for these photos will just go to the page (this page actually) and just save it. They may not read other pages, which I have some advertisements placed there. I may lose my commissions.
But what the heck, I uploaded all these things for the benefit of the readers anyway.
So I have decided to grant their requests. I am not going to insert all these photographs today. But I will do it gradually because it takes time. I will not just insert the pictures into this page, anybody can do that. But I will add some comment to each of the pics so there will be some information that goes with each picture.
A picture may say a thousand words, but they may be in languages you do not understand. So I need to attach some comments and that will take a little time and thinking. I am not a writer by nature.
Okay, enough talk. The first pictures are about fireman switch installation.
Enjoy.
Picture 2 – Fireman switch installation
Picture 3 - Fireman switches for high-rise buildings
For readers without electrical background, these are the emergency electrical isolation switch installed and to be used by the firemen when they want to fight fire the building.
EMERGENCY LIGHTING INSTALLATION PICTURES
Most countries have statutory provisions that require the installation of emergency lights in all buildings exceeding certain sizes. These lights need to be provided at strategic locations throughout the building to assist in the evacuation of the building occupants during fire situations or other types of emergencies.
Practically this emergency lighting is useful even without the emergency and during daytime. When the mains power fails, there is a certain time delay before the backup power supply can take over. The standby electric generator, the most usual form of backup emergency power in normal buildings, take quite second to get warmed up and provide the supply to essential services inside the building.
Some internal corridors in large buildings can be very dark without electrical lighting. Serious accidents can happen if the corridor suddenly becomes dark. Even with a little stray lights from windows somewhere, the eyes take a little bit of time to adjust to the sudden change of light level.
Some internal rooms inside air-conditioned buildings are totally windowless. Even with windows, the daylight from outside the building may not reach the rooms. During power failures, these rooms can be darker than nighttime out in the open air outside. At least outside there you can rely on a little light from the stars or the moon. Again, in this type of darkness, anything can happen.
The self-contained emergency light fittings are usually installed at all exit routes and at all places where uninterrupted lighting is required. In the second situation this lights serve the dual functions of a fire related equipment and a normal lighting (with much reduced lighting level).
The emergency light fittings are connected to the essential supply of the building electrical system. This way the rechargeable storage battery is charged even during normal power failure (i.e. when the standby electrical generator is running).
You can read more details on this issue at my other post, emergency lights installation.
Today I have uploaded few pictures showing the method of installing a ceiling-recessed emergency lighting (EL) unit. This work was photographs at a high-rise building construction a few months ago.
As far as the choice of types of the EL light, I would personally prefer a surface mounted self-contained type. The one being installed in this picture is also a battery-backed self-contained type, but it is recessed mounted.
You can see below two pictures showing how a ceiling-recessed emergency light fitting is being installed. There are more pictures of the installation that you can see at this post, Emergency light installation pics. I did not link all the pictures to this post because that will make this post too long after a while.
This post will also be the main page for all the pictures that I uploaded to this blog. If I link all of them here, the page will also take too long to download. People with slow connections may have problem downloading this page.
Picture 4 – Side view of the ceiling-recessed emergency light installation
Picture 5 – Top view, from above the ceiling panel, to show how it is fixed to the board
Cable trays and cable ladder pictures
I have uploaded a few pictures and a diagram on the installation of electrical cable trays and cable ladders for those who have some need for them.
You can see all the cable tray pictures at this post, Cable tray and ladder installation.
If you are looking for pictures on cable ladders, I have uploaded one at this post, Electrical cable ladder pictures. More pics will be coming soon.
At the end of these pictures, you will also find a sample specification for the cable tray and cable ladder installations in multi-storey office buildings. If you wish to see more photos of electrical installations, visit my other post, Electrical installation pictures.
Picture 6 – Cable tray at high level inside a chiller plant room
Cable trays for the installation of electric power cables are usually specified as perforated hot-dipped galvanized sheet steel.
The term perforated usually is defined as holes provided to the sheet of the trays to allow the movement of airflow that can provide a more natural flow of air circulation around the electric cables. This air movement can effectively help cool the cables on the tray.
All electric cables carrying current dissipate some power because of the resistance of the current carrying conductors.
If the energy dissipated in the form of heat is not carried away from the cables, the cables will heat themselves up and effectively operate at the higher temperature than the actual surrounding air. This will lower the actual maximum current that the cables can actually handle.
This IEE Regulation provides a table of current carrying capacities of cables that are run on perforated cable trays. However, these cable ratings are only applicable if the holes occupy at least 30 percent of the surface area of the trays.
Photo 7 – Underground electrical ducts crossing a roadside drain
Today I have uploaded a few photographs of underground cable ducts crossing a roadside drain at a project site a couple of months ago.
A good design of external electrical works would have considered the situations where all the different services would cross each other.
Even when they do not cross each other, the space where all the services need to be installed may become smaller or narrower.
Therefore a good design engineer need to foresee these potential problems that may be too difficult or too expensive to be solved by the trade contractors, engineers and managers during the construction stage.
In some construction environments, all designs from the respective design consultants and engineers would be passed through a coordination stage. There the detailed design drawings are superimposed over each other.
Read the full article at this post, Cable ducts crossing roadside drain.
Photo 8 – A switch center at a small meeting room
The following materials can be used as a performance specification for installation of socket outlets and switches in multi-storey office buildings. I will also add some pictures of actual installations of these devices in future, and may be also some drawings and diagrams. Come back and check out this post every few weeks.
Read the full article at this post, Socket outlets and switch installations. There are more photos at this post also, Metalclad electrical sockets.
Photo 8 – Armored XLPE cables and fire rated (FR) cables on cable tray inside an electrical riser shaft
The following sample specifications cover the installation of PVC, XLPE, PILC and MICC cables in a new high-rise office building. Read the full article at this post, PVC PILC XLPE MICC cable installation .
Photo 9 – Armored XLPE cables on cable tray
One length of underground armored cable is used. Underground means the cable is installed inside the ground about 3 ft below the surface.
Armored cable cost much more because of the steel wire armor protecting the cable from physical damage. The letters SWA in the cable tag “XLPE/SWA/PVC” is an acronym for “steel wire armor”.
“XLPE” at the front means the insulation of the cable conductor. When we say a cable, the terminology is actually not precise enough.
In this case, inside the incoming supply cable there is actually 4 inner cores each with an electrical insulation. Therefore, each of the four insulated inner cores (the inner core is usually made of either copper or aluminium) is a complete electrical cable by itself.
The four of them are bunched together to make it easier to run and it can reduce the cost. We can actually use 4 independent cables instead of one cable with 4 inner insulated cores.
Read the complete article at this post, Intro to XLPE armored cables.
Photo 10 – Wall-mounted surface conduit
The above photo shows the distance between two draw-boxes in a surface-mounted conduit system. Click here to go back to electric conduit installation.
The photograph shows two metal conduits run on the surface of a wall. Here I just wanted to show the distance between the two draw boxes on the upper conduit. This maximum distance should be 9 meter if the requirements of the specifications are to be strictly followed.
Read the full article at this post, distance between conduit draw boxes.
Photo 11 - The continuous ring type of identification ferrules
This type of wiring identification material has been around for some time and it is still widely used. Each of the letters of the identification tag requires one piece of the ring.
So if the wiring identification number contains 6 characters of letters, then 6 pieces of the rings would be required.
Needless to say, the task to install these type of identification ferrules can be quite tedious and time consuming. It is simply an additional cost to the cost of the DB.
Read the full article at this post, DB wiring identification ferrules. However, this article is just a supplement to a previous post which was actually a sample specifications, Electrical DB wiring.
Photo 12 - View of the lower part of a main switchboard
You may be wondering why I did not stand back a little bit and take a wider view of the subswitchboard. The would give a nicer picture, right?
I however took this picture when the main switchboard (MSB) has already been located on its actual position in the electrical switchroom (LV Switchroom).
Usually the layout of an electrical LV room is such that the main switchboard is located near the wall of the room. The space behind the board is usually between 600mm to 1000mm between the back of the switchboard and the wall.
In fact 750mm is a more common space clearance for office and residential building. This of from my own personal experience. I do see projects where the architects were more generous.
In those cases you may then find that the clearance is between 1000mm to 1300mm.
Read the rest of the post here, Switchboard earthing busbar. There is also a simple performance specifications on this topic (Switchboard electrical earthing) for readers who need it.
Photo 13 - A switchboard being unloaded from the transport at a construction site of a building project
Switchboards are the switching centers of the low voltage distribution sytem. They are also the places where the control and protection system is located.
Because of the importance of these equipment, all aspects of a switchboard installation need to be closely monitored. Even the loading and unloading of them to and from the transport need to be monitored.
Read the rest of the post here, switchboard installation check.
The above is a picture of two units of under floor service boxes with 13A switched socket outlets installed.
Is there any problem here?
Image 15 - 4 ft 36 Watt Wall-mounted Fluorescent Light Symbol
For readers who are looking for a simple house electrical symbols, you may wish to visit this post, House electrical symbols. I have uploaded a list of symbols for a small house.
This post, Home electrical wiring, symbols and checking, is the original post. It is very long. That's why I am trying to break it up into smaller posts for the the benefit of readers who are looking for the information contained in the long post.
This post on electrical symbols is the first of such posts.
The above image on meter panel comes from the second small post. This time it about a simple house electrical schematic. Read it here, Simple house electrical schematic.
I just uploaded this simple electrical layout for a small two bedroom house. You can read the rest of the article at this post, Simple house electrical layout.
The above is a picture of electrical earth rod inside an inspection chamber. This is a copper-jacketed steel rod with 16mm diameter.
The earthing system at this project was not yet completed at this point time.
This is to make sure that the chamber can be properly set to the finish level of the road.
Here the rod and chamber were already in place, just waiting for the final tar coating.
See more pictures of eartg rods here, Copper earth rod pictures. There is also a simple specifications for installing electrical earthing system for high voltage substations at this post, Electrical earthing system.
Diagram 19 – Fault current path
While we are on the subject of electrical grounding, the above is a current path diagram that I did for an article about electric shock protection some time back.
It was a long article. Not pretty but it sure does have some real information if you need some. Read the article at this post, Home electrical earth installation.
This is a lift motor room layout for an eight storey hostel block. I uploaded part drawing this as materials for the discussion on electrical rooms design.
Read the post here, Lift motor room layout drawing.
Picture 21 - Neutral link of main incoming circuit breaker
Read the full article here, Neutral link pictures.
Copyright http://electricalinstallationblog.blogspot.com/ Free electric installation pictures
Photo 1 - Electrical services inside a building
Jokes aside, actually I received a few emails from some friends in the education business (i.e. local universities) complaining that they like the real construction pictures and the temporary electrical installation pictures that I uploaded to this blog (visit the anchor post here, Temporary Electrical Installations).
However, the pictures are scattered all over the place. A few of them suggested that I put these pictures into one post and the same for the electrical schematics.
I know these people wanted to use these photos and electrical diagrams for their teaching works. Part of me feels the reluctance to this step because I know these real construction photos have some monetary values.
If I locate them at one place, then many readers who are hunting for these photos will just go to the page (this page actually) and just save it. They may not read other pages, which I have some advertisements placed there. I may lose my commissions.
But what the heck, I uploaded all these things for the benefit of the readers anyway.
So I have decided to grant their requests. I am not going to insert all these photographs today. But I will do it gradually because it takes time. I will not just insert the pictures into this page, anybody can do that. But I will add some comment to each of the pics so there will be some information that goes with each picture.
A picture may say a thousand words, but they may be in languages you do not understand. So I need to attach some comments and that will take a little time and thinking. I am not a writer by nature.
Okay, enough talk. The first pictures are about fireman switch installation.
Enjoy.
Picture 2 – Fireman switch installation
Picture 3 - Fireman switches for high-rise buildings
For readers without electrical background, these are the emergency electrical isolation switch installed and to be used by the firemen when they want to fight fire the building.
EMERGENCY LIGHTING INSTALLATION PICTURES
Most countries have statutory provisions that require the installation of emergency lights in all buildings exceeding certain sizes. These lights need to be provided at strategic locations throughout the building to assist in the evacuation of the building occupants during fire situations or other types of emergencies.
Practically this emergency lighting is useful even without the emergency and during daytime. When the mains power fails, there is a certain time delay before the backup power supply can take over. The standby electric generator, the most usual form of backup emergency power in normal buildings, take quite second to get warmed up and provide the supply to essential services inside the building.
Some internal corridors in large buildings can be very dark without electrical lighting. Serious accidents can happen if the corridor suddenly becomes dark. Even with a little stray lights from windows somewhere, the eyes take a little bit of time to adjust to the sudden change of light level.
Some internal rooms inside air-conditioned buildings are totally windowless. Even with windows, the daylight from outside the building may not reach the rooms. During power failures, these rooms can be darker than nighttime out in the open air outside. At least outside there you can rely on a little light from the stars or the moon. Again, in this type of darkness, anything can happen.
The self-contained emergency light fittings are usually installed at all exit routes and at all places where uninterrupted lighting is required. In the second situation this lights serve the dual functions of a fire related equipment and a normal lighting (with much reduced lighting level).
The emergency light fittings are connected to the essential supply of the building electrical system. This way the rechargeable storage battery is charged even during normal power failure (i.e. when the standby electrical generator is running).
You can read more details on this issue at my other post, emergency lights installation.
Today I have uploaded few pictures showing the method of installing a ceiling-recessed emergency lighting (EL) unit. This work was photographs at a high-rise building construction a few months ago.
As far as the choice of types of the EL light, I would personally prefer a surface mounted self-contained type. The one being installed in this picture is also a battery-backed self-contained type, but it is recessed mounted.
You can see below two pictures showing how a ceiling-recessed emergency light fitting is being installed. There are more pictures of the installation that you can see at this post, Emergency light installation pics. I did not link all the pictures to this post because that will make this post too long after a while.
This post will also be the main page for all the pictures that I uploaded to this blog. If I link all of them here, the page will also take too long to download. People with slow connections may have problem downloading this page.
Picture 4 – Side view of the ceiling-recessed emergency light installation
Picture 5 – Top view, from above the ceiling panel, to show how it is fixed to the board Cable trays and cable ladder pictures
I have uploaded a few pictures and a diagram on the installation of electrical cable trays and cable ladders for those who have some need for them.
You can see all the cable tray pictures at this post, Cable tray and ladder installation.
If you are looking for pictures on cable ladders, I have uploaded one at this post, Electrical cable ladder pictures. More pics will be coming soon.
At the end of these pictures, you will also find a sample specification for the cable tray and cable ladder installations in multi-storey office buildings. If you wish to see more photos of electrical installations, visit my other post, Electrical installation pictures.
Picture 6 – Cable tray at high level inside a chiller plant room
Cable trays for the installation of electric power cables are usually specified as perforated hot-dipped galvanized sheet steel.
The term perforated usually is defined as holes provided to the sheet of the trays to allow the movement of airflow that can provide a more natural flow of air circulation around the electric cables. This air movement can effectively help cool the cables on the tray.
All electric cables carrying current dissipate some power because of the resistance of the current carrying conductors.
If the energy dissipated in the form of heat is not carried away from the cables, the cables will heat themselves up and effectively operate at the higher temperature than the actual surrounding air. This will lower the actual maximum current that the cables can actually handle.
This IEE Regulation provides a table of current carrying capacities of cables that are run on perforated cable trays. However, these cable ratings are only applicable if the holes occupy at least 30 percent of the surface area of the trays.
Photo 7 – Underground electrical ducts crossing a roadside drain
Today I have uploaded a few photographs of underground cable ducts crossing a roadside drain at a project site a couple of months ago.
A good design of external electrical works would have considered the situations where all the different services would cross each other.
Even when they do not cross each other, the space where all the services need to be installed may become smaller or narrower.
Therefore a good design engineer need to foresee these potential problems that may be too difficult or too expensive to be solved by the trade contractors, engineers and managers during the construction stage.
In some construction environments, all designs from the respective design consultants and engineers would be passed through a coordination stage. There the detailed design drawings are superimposed over each other.
Read the full article at this post, Cable ducts crossing roadside drain.
Photo 8 – A switch center at a small meeting room
The following materials can be used as a performance specification for installation of socket outlets and switches in multi-storey office buildings. I will also add some pictures of actual installations of these devices in future, and may be also some drawings and diagrams. Come back and check out this post every few weeks.
Read the full article at this post, Socket outlets and switch installations. There are more photos at this post also, Metalclad electrical sockets.
Photo 8 – Armored XLPE cables and fire rated (FR) cables on cable tray inside an electrical riser shaft
The following sample specifications cover the installation of PVC, XLPE, PILC and MICC cables in a new high-rise office building. Read the full article at this post, PVC PILC XLPE MICC cable installation .
Photo 9 – Armored XLPE cables on cable tray
One length of underground armored cable is used. Underground means the cable is installed inside the ground about 3 ft below the surface.
Armored cable cost much more because of the steel wire armor protecting the cable from physical damage. The letters SWA in the cable tag “XLPE/SWA/PVC” is an acronym for “steel wire armor”.
“XLPE” at the front means the insulation of the cable conductor. When we say a cable, the terminology is actually not precise enough.
In this case, inside the incoming supply cable there is actually 4 inner cores each with an electrical insulation. Therefore, each of the four insulated inner cores (the inner core is usually made of either copper or aluminium) is a complete electrical cable by itself.
The four of them are bunched together to make it easier to run and it can reduce the cost. We can actually use 4 independent cables instead of one cable with 4 inner insulated cores.
Read the complete article at this post, Intro to XLPE armored cables.
Photo 10 – Wall-mounted surface conduit
The above photo shows the distance between two draw-boxes in a surface-mounted conduit system. Click here to go back to electric conduit installation.
The photograph shows two metal conduits run on the surface of a wall. Here I just wanted to show the distance between the two draw boxes on the upper conduit. This maximum distance should be 9 meter if the requirements of the specifications are to be strictly followed.
Read the full article at this post, distance between conduit draw boxes.
Photo 11 - The continuous ring type of identification ferrules
This type of wiring identification material has been around for some time and it is still widely used. Each of the letters of the identification tag requires one piece of the ring.
So if the wiring identification number contains 6 characters of letters, then 6 pieces of the rings would be required.
Needless to say, the task to install these type of identification ferrules can be quite tedious and time consuming. It is simply an additional cost to the cost of the DB.
Read the full article at this post, DB wiring identification ferrules. However, this article is just a supplement to a previous post which was actually a sample specifications, Electrical DB wiring.
Photo 12 - View of the lower part of a main switchboard
You may be wondering why I did not stand back a little bit and take a wider view of the subswitchboard. The would give a nicer picture, right?
I however took this picture when the main switchboard (MSB) has already been located on its actual position in the electrical switchroom (LV Switchroom).
Usually the layout of an electrical LV room is such that the main switchboard is located near the wall of the room. The space behind the board is usually between 600mm to 1000mm between the back of the switchboard and the wall.
In fact 750mm is a more common space clearance for office and residential building. This of from my own personal experience. I do see projects where the architects were more generous.
In those cases you may then find that the clearance is between 1000mm to 1300mm.
Read the rest of the post here, Switchboard earthing busbar. There is also a simple performance specifications on this topic (Switchboard electrical earthing) for readers who need it.
Photo 13 - A switchboard being unloaded from the transport at a construction site of a building project
Switchboards are the switching centers of the low voltage distribution sytem. They are also the places where the control and protection system is located.
Because of the importance of these equipment, all aspects of a switchboard installation need to be closely monitored. Even the loading and unloading of them to and from the transport need to be monitored.
Read the rest of the post here, switchboard installation check.
Photo 14 – 13A switched socket outlets inside underfloor junction boxes
The above is a picture of two units of under floor service boxes with 13A switched socket outlets installed.
Is there any problem here?
I took this picture some two or three years ago. Shown in the picture are two service boxes for an underfloor trunking system.
For the benefit of readers who are not very familiar with the term underfloor trunking, underfloor junction boxes, and underfloor service boxes and how they relate to each other, please refer to the layout drawing below.
Please visit the post, 13A sockets inside underfloor box, to read the rest of the article.Image 15 - 4 ft 36 Watt Wall-mounted Fluorescent Light Symbol
For readers who are looking for a simple house electrical symbols, you may wish to visit this post, House electrical symbols. I have uploaded a list of symbols for a small house.
This post, Home electrical wiring, symbols and checking, is the original post. It is very long. That's why I am trying to break it up into smaller posts for the the benefit of readers who are looking for the information contained in the long post.
This post on electrical symbols is the first of such posts.
Image 16 – The electric meter panel symbol
The above image on meter panel comes from the second small post. This time it about a simple house electrical schematic. Read it here, Simple house electrical schematic.
Drawing 17 – An electrical layout drawing for a two-bedroom small house
I just uploaded this simple electrical layout for a small two bedroom house. You can read the rest of the article at this post, Simple house electrical layout.
Picture 18 – An earthing rod installed inside a precast concrete inspection chamber
The above is a picture of electrical earth rod inside an inspection chamber. This is a copper-jacketed steel rod with 16mm diameter.
The earthing system at this project was not yet completed at this point time.
However, the project was nearing the end of the construction period. Since this earth rod inspection chamber was by the side of a service road near the plant-room area, the installation of the rod and chamber needed to wait until the road crusher run has been laid.
This is to make sure that the chamber can be properly set to the finish level of the road.
Here the rod and chamber were already in place, just waiting for the final tar coating.
See more pictures of eartg rods here, Copper earth rod pictures. There is also a simple specifications for installing electrical earthing system for high voltage substations at this post, Electrical earthing system.
Diagram 19 – Fault current path
While we are on the subject of electrical grounding, the above is a current path diagram that I did for an article about electric shock protection some time back.
It was a long article. Not pretty but it sure does have some real information if you need some. Read the article at this post, Home electrical earth installation.
Diagram 20 – A ground floor layout of building services
I just sent an article about electrical risers at this post, Electrical riser rooms.
There was also an article about electrical risers that I sent some time ago at this post, Electrical rooms design. However, this is more of an overview of the design planning for electrical rooms.
Part Drawing 21 – The lift motor room layout drawing
I just sent an article about electrical risers at this post, Electrical riser rooms.
There was also an article about electrical risers that I sent some time ago at this post, Electrical rooms design. However, this is more of an overview of the design planning for electrical rooms.
Part Drawing 21 – The lift motor room layout drawing
This is a lift motor room layout for an eight storey hostel block. I uploaded part drawing this as materials for the discussion on electrical rooms design.
Read the post here, Lift motor room layout drawing.
Picture 21 - Neutral link of main incoming circuit breaker
Electrical fuses and neutral links are among the most commonly discussed items on consumers’ discussion forums such as Yahoo Answers, etc.
Many times, the higher the number of people who gets involved in a trying to answer a simple electrical question, the more confused the issue becomes.
Instead of understanding more, many beginners often get confused and sometimes misled.
A few pictures or diagrams could have made a significant difference to the beginners who were trying to understand some basics of electrical installations. But then I guess many of those forums do not provide facilities for attachment of graphics.
Read the full article here, Neutral link pictures.
Copyright http://electricalinstallationblog.blogspot.com/ Free electric installation pictures
Wednesday, January 6, 2010
How you get electric shocks
I have sent a lengthy article to this blog some time back on how a person can happen to get electrical shock. However, some readers complained that it was too long that they have difficulties finding what they want to read about. Therefore, I have decided to write a few short articles on subtitles covered by that post for the benefits of casual readers who are looking for only certain very specific issues. This post is the first of those subtitles.
Look at the four beautiful diagrams that I just created below.
Diagram 1 – Touching live electrical wire and the neutral wire
THE SIMPLE LOGIC OF ELECTRIC SHOCKS
Electric shock happens when a certain amount of electrical current happen to flow through a person’s body for whatever reason. The human body has not been designed to conduct electricity above a certain current level or miliamperes. The above-mentioned post on electric shock protection gives a detailed description on the levels of current that can cause injuries and electrocutions. You can read it here, ELCB - Home Electrical Shock Protection, if you wish to know them in more details.
What happen when the electrical current flow through the body? At a lower level, the current interferes with the nervous system. That is why when someone accidentally holds a live wire with her hand, she may not be able to let go of the wire. In fact, her fingers may even grip the live wire tighter, resulting in a much better contact between the hand and the wire. This will result in lower contact resistance that will further increase the current flow and therefore more serious injuries. If you visit this post, Electrical injury pictures, you can see the pictures of how serious the electrical injuries can be.
The higher the shock current, the more severe the injuries
If the shock current is higher, then the body tissue where the current flows will get damaged. The higher the current, the more serious the damage. At 10mA, the victim may still be able to control his arm and instinctively release the electrified object or wire he is holding. However that is about the maximum shock current that he can handle. If the shock current is higher, he would lose control of the arm. The hand grip on the tool may get stronger, resulting in higher current flow.
At 100 mili-amperes (that is 0.1A), the victim faces a certain death if he sustains that level of shock current flow for 2 seconds or more.
The degree of injuries depends on which body parts the shock current flow through
The path where the shock current travels through the body also will have some effects on how serious the injuries can be. If a person touches a live wire by his right hand while standing on a grounded metal part, the electric current flow through from the live wire through the hand, the arm and shoulder, the chess, legs and down to the metal part. In this case, the current can damage the victim’s heart while flowing through the chess. At 30 mili-amperes, the victim may even stop breathing (respiratory paralysis).
The higher the voltage, the more serious the injuries
The higher the voltage, the more serious the resulting injuries. At 600 volts, the electric shock current can be as high as 4 amperes. This level of current can seriously damage the victim’s heart and other internal organs. The skin where the body makes contact with the live wire can be burned. The tissue damages are so serious that a limb on the path of the flow of the shock current can come off the victim’s body.
The longer the current flow through the victims body, the more serious the injuries
As I said above, at 100 mili-amperes, the victim faces a certain death if that level of current continues to flow through the body for more than 2 seconds. This is very useful information for those who work on live electrical parts either by occupation or just a do-it-yourself (DIY) working on a live house wiring.
The way you stand or the way you access the live parts should be in such a way as to make the duration of contact with the live part as short as possible in the event of accidental contact. Of course, you must at all times de-energize the faulty part before starting on the repair works. However this advise very often are just ignored by some people either because they feel they are skilled enough to work on live parts, or they just don’t bother much with their own safety.
Whatever the reasons are, you can actually position yourself such a way that at the moment of accidental contact, your reflexes will cause your body to break contact immediately. This quick contact break will mean life or death.
About a week ago, a news broke out about a fatal accident involving electrical works has occurred at a project not far from the jobsite I was working on. After some checking, I finally found out what actually has happened that led to the immediate death of the worker. Actually he was trying to cut an insulated electric wire inside a recently completed building. The building has just been handed over to the client and most of the tenants were busy with their own renovations works before they actually move in to the new place.
So the worker was trying to cut a live internal wiring that was supposed to have been dead and isolated by a colleague. As it happened, his colleague isolated a wrong circuit breaker on the electrical DB.
We can talk about isolation procedures in other posts. What I wish to point out here is the way the tool is handled in the case of a wire cutting. The cutter is held with the palm of the hand and a few fingers forming a strong grip. This form of hand action is difficult to let go in the case of an accidental contact.
Some other forms of hand action will more likely result in breaking contact by the body reflexes as the electric shock is sensed. One example is the turning of a termination screw at a circuit breaker terminal using a screwdriver. This sort of issue can be quite subjective and different persons may handle a tool a bit differently. But I think all experienced technicians agree that there is a room there to make the injuries less severe if it has to happen.
The higher the skin contact resistance, the lower the shock current
What does this mean in layman terms? I know these electrical terms can be intimidating to some people. However, electrical safety should be an issue for concern to everyone who use electricity on his or her houses or at their workplaces.
Look at Diagram 1 again. In this case, the girl is almost touching two electrical wires. When both hands touches the wires, the shock current can travel from the left hand holding the red live wire to the right hand holding the black neutral wire.
How much current will actually flow?
That depends on three things. 1. How many volts of voltage at the red live wire; 2. How many volts of voltage at the neutral black wire; 3. How much resistance is presented by the body against the current flow from left hand to the right hand.
Let’s answer this question one by one. For question 1, if you live in London, that voltage may be 220 volts. (Note: Do not get confused by the “volts” terminology. A volt is like speed. 3A or 3 amperes is like 3 meter per second, not like 3 apples per basket.) If you live in Kuala Lumpur, that voltage level may be 240 volts.
However if you live in Los Angeles, your house power sockets will have 110 volt supply. So the red wire there will have 110 volts of voltage.
For question 2: The voltage there will probably be zero volts in all the three cities mentioned above. However there are situations where the voltage at the neutral wire there is not zero. So the neutral wire is not always safe. Always keep this in mind when working on electrical wiring or equipment.
Before we go to question 3, let us do a little bit of calculations first. Since the voltage at the left hand is 240 volts (assuming you are visiting Kuala Lumpur), and 0 volt at the right hand, then the voltage different between the two points is
240 – 0 = 240 volts.
An electrician will call this a 240 volts of potential difference. If the black neutral wire is injured somewhere on the floor, and it touch a live faulty equipment which is at 200 volts, then the potential difference is
240 – 200 = 40 volt, which is a lower value (and hopefully less dangerous).
So how much shock current will flow through the girl’s body if the potential difference is 240 volts (assuming 240 – 0 volts)?
That will depend on how much resistance is presented by the girl’s body against current flow from the live wire and the neutral wire.
So how much is the normal body resistance? This is actually Question No 3 above.
Well, when the skin is dry, the body can present a resistance as high as 100,000 ohms (that is 100 kilo-ohms) against the current flow.
The magnitude of current is lower as the body resistance goes higher. So in this case, the magnitude of the shock current will be:
Shock current = voltage difference divided by body resistance
= 240 volt / 100,000 ohm
= 0.0024 ampere
That is 2.4 thousandth of an ampere of electric current flow, or 2.4 mili-amperes, or 2.4 mA.
How much damage will this amount of current do to the human body? Again you can see the detail list of the injuries in the above-mentioned post. However I listed a few of them here for easy comparison and to help you appreciate the size of this shock current from the viewpoint of injuries that it can cause.
At 1 mA – a normal person would feel a slight tingling sensation.
At 5 mA - A light shock will be felt, but most persons will be able to “let go”. Not a painful feeling, but definitely disturbing. However, a strong reflexive movement by the victim can cause further accidents and other type of injuries.
At 6 to 30 mA - The victim can be paralyzed, or the muscles will freeze (will not be able to release a tool, wire, or other object).
Painful, and my not be possible to let go.
At high voltage (above 600 Volt), this current can already cause severe burns.
As you can see above, at 5 mili-amperes or below, a normal person should still be able to let go the electrified object the he accidentally came into contact with. So a person with dry skin would be less likely to suffer severe injuries if he accidentally comes into contact with a 240 volts live wire. A 110 volts domestic voltage at American house will be less than half of that shock current, so it would be safer theoretically (the American safety follows a different standard so we cannot really compare them apple to apple).
Now let’s see what will happen when the skin is wet. The wet condition can result in a very much lower skin resistance to electric shock current. It can be as low as 1,000 ohms. Therefore the shock current is
Shock current = 240 divided 1000
= 0.24 ampere, which is 240 mili amperes!
From the list that I copied above, at 30 mA the victim would surely not be able to let go of the electrified object he was holding. Therefore the shock current through the body will eventually rise to the maximum that is limited by the body resistance which is 240 mA.
So the victim can suffer a maximum level of injuries. The list on the other post says:
(At 75 mili-Amperes and above – The victim undergo ventricular fibrillation (very rapid, ineffective heartbeat). This condition can cause death within a few minutes. The only way to save the victim is by a special device called defibrillator.
So there you have it. The comparison of the level of resulting injuries between the lowest and the highest skin contact resistances.
BASIC CASES OF ELECTRIC SHOCKS
I started out this post with the intention of explaining about how someone can get electric shocks. But I seem to have spent this far explaining more on the logics of electric shocks.
However, the understanding of the working principles, or the mechanics, behind these accidents will be more useful to you in achieving the most important objective: that is to prevent all serious injuries that result from electrical shocks.
It would be nice to be able to prevent electrical accidents altogether. However as any construction man would testify, it is near to impossible to prevent accidents at construction sites.
The rough environment that a temporary electrical installation is subjected to, the nature of the electrical users at the jobsite, and the difficulties faced by persons responsible on electrical safety on large construction sites to ensure adequate level of safety habits are actually practiced throughout the construction grounds and floors. These three constraints make it near impossible to totally prevent electrical accidents on large construction sites with thousands of workers, especially those with small site areas such as high rise construction at city centers.
What we can do is to minimize the degree of electrical injuries when they do occur.
However, electrical accidents at home or office can still be prevented totally. That is my opinion.
Now THE how to get electric shock No 1. As shown in Diagram 1 at high up in the beginning of this post, that can happen when two locations on the human body came into contact with conductive parts at two different voltages. I have used this diagram to explain the whole upper part of this post above. So that should be enough.
Diagram 2 -Touching live and earth wire
In this case, the right hand came into contact with the earth wire instead of the neutral wire shown in Diagram 1. The result can be similar. I said “can be” instead of “will be”. Why? Because in this case, the live red wire can be installed with an electric shock protection device that will sense this shock current.
The devise is the ELCB (earth leakage circuit breaker). Other names are also used to explain this function in an electrical installation such as RCD (residual current devices), GFCI (ground fault circuit interrupters), etc. Read this post ELCB Circuit to know more how this device functions.
Diagram 3 – When the hand touches a live wire and the person is not separated at the feet from the ground with purpose-made electrical insulation means like rubber shoes, the rubber mat in front of the switchboards in electrical rooms, etc.
Diagram 4 – When there is simultaneous contacts with fault electric motors and ground.
The electric motor can be any electric equipment or appliances. The same process of electric shock current flow will happen.
There are more points that I wish to write down here. However it’s already almost three AM and I have to go to work tomorrow. So I will continue this some other time, in another post.
Stay safe. Electricity kills.
RELATED ARTICLES: a) Home electrical wiring, symbols and checking;
Copyright http://electricalinstallationblog.blogspot.com/ How you get electric shocks
Look at the four beautiful diagrams that I just created below.
Diagram 1 – Touching live electrical wire and the neutral wire
THE SIMPLE LOGIC OF ELECTRIC SHOCKS
Electric shock happens when a certain amount of electrical current happen to flow through a person’s body for whatever reason. The human body has not been designed to conduct electricity above a certain current level or miliamperes. The above-mentioned post on electric shock protection gives a detailed description on the levels of current that can cause injuries and electrocutions. You can read it here, ELCB - Home Electrical Shock Protection, if you wish to know them in more details.
What happen when the electrical current flow through the body? At a lower level, the current interferes with the nervous system. That is why when someone accidentally holds a live wire with her hand, she may not be able to let go of the wire. In fact, her fingers may even grip the live wire tighter, resulting in a much better contact between the hand and the wire. This will result in lower contact resistance that will further increase the current flow and therefore more serious injuries. If you visit this post, Electrical injury pictures, you can see the pictures of how serious the electrical injuries can be.
The higher the shock current, the more severe the injuries
If the shock current is higher, then the body tissue where the current flows will get damaged. The higher the current, the more serious the damage. At 10mA, the victim may still be able to control his arm and instinctively release the electrified object or wire he is holding. However that is about the maximum shock current that he can handle. If the shock current is higher, he would lose control of the arm. The hand grip on the tool may get stronger, resulting in higher current flow.
At 100 mili-amperes (that is 0.1A), the victim faces a certain death if he sustains that level of shock current flow for 2 seconds or more.
The degree of injuries depends on which body parts the shock current flow through
The path where the shock current travels through the body also will have some effects on how serious the injuries can be. If a person touches a live wire by his right hand while standing on a grounded metal part, the electric current flow through from the live wire through the hand, the arm and shoulder, the chess, legs and down to the metal part. In this case, the current can damage the victim’s heart while flowing through the chess. At 30 mili-amperes, the victim may even stop breathing (respiratory paralysis).
The higher the voltage, the more serious the injuries
The higher the voltage, the more serious the resulting injuries. At 600 volts, the electric shock current can be as high as 4 amperes. This level of current can seriously damage the victim’s heart and other internal organs. The skin where the body makes contact with the live wire can be burned. The tissue damages are so serious that a limb on the path of the flow of the shock current can come off the victim’s body.
The longer the current flow through the victims body, the more serious the injuries
As I said above, at 100 mili-amperes, the victim faces a certain death if that level of current continues to flow through the body for more than 2 seconds. This is very useful information for those who work on live electrical parts either by occupation or just a do-it-yourself (DIY) working on a live house wiring.
The way you stand or the way you access the live parts should be in such a way as to make the duration of contact with the live part as short as possible in the event of accidental contact. Of course, you must at all times de-energize the faulty part before starting on the repair works. However this advise very often are just ignored by some people either because they feel they are skilled enough to work on live parts, or they just don’t bother much with their own safety.
Whatever the reasons are, you can actually position yourself such a way that at the moment of accidental contact, your reflexes will cause your body to break contact immediately. This quick contact break will mean life or death.
About a week ago, a news broke out about a fatal accident involving electrical works has occurred at a project not far from the jobsite I was working on. After some checking, I finally found out what actually has happened that led to the immediate death of the worker. Actually he was trying to cut an insulated electric wire inside a recently completed building. The building has just been handed over to the client and most of the tenants were busy with their own renovations works before they actually move in to the new place.
So the worker was trying to cut a live internal wiring that was supposed to have been dead and isolated by a colleague. As it happened, his colleague isolated a wrong circuit breaker on the electrical DB.
We can talk about isolation procedures in other posts. What I wish to point out here is the way the tool is handled in the case of a wire cutting. The cutter is held with the palm of the hand and a few fingers forming a strong grip. This form of hand action is difficult to let go in the case of an accidental contact.
Some other forms of hand action will more likely result in breaking contact by the body reflexes as the electric shock is sensed. One example is the turning of a termination screw at a circuit breaker terminal using a screwdriver. This sort of issue can be quite subjective and different persons may handle a tool a bit differently. But I think all experienced technicians agree that there is a room there to make the injuries less severe if it has to happen.
The higher the skin contact resistance, the lower the shock current
What does this mean in layman terms? I know these electrical terms can be intimidating to some people. However, electrical safety should be an issue for concern to everyone who use electricity on his or her houses or at their workplaces.
Look at Diagram 1 again. In this case, the girl is almost touching two electrical wires. When both hands touches the wires, the shock current can travel from the left hand holding the red live wire to the right hand holding the black neutral wire.
How much current will actually flow?
That depends on three things. 1. How many volts of voltage at the red live wire; 2. How many volts of voltage at the neutral black wire; 3. How much resistance is presented by the body against the current flow from left hand to the right hand.
Let’s answer this question one by one. For question 1, if you live in London, that voltage may be 220 volts. (Note: Do not get confused by the “volts” terminology. A volt is like speed. 3A or 3 amperes is like 3 meter per second, not like 3 apples per basket.) If you live in Kuala Lumpur, that voltage level may be 240 volts.
However if you live in Los Angeles, your house power sockets will have 110 volt supply. So the red wire there will have 110 volts of voltage.
For question 2: The voltage there will probably be zero volts in all the three cities mentioned above. However there are situations where the voltage at the neutral wire there is not zero. So the neutral wire is not always safe. Always keep this in mind when working on electrical wiring or equipment.
Before we go to question 3, let us do a little bit of calculations first. Since the voltage at the left hand is 240 volts (assuming you are visiting Kuala Lumpur), and 0 volt at the right hand, then the voltage different between the two points is
240 – 0 = 240 volts.
An electrician will call this a 240 volts of potential difference. If the black neutral wire is injured somewhere on the floor, and it touch a live faulty equipment which is at 200 volts, then the potential difference is
240 – 200 = 40 volt, which is a lower value (and hopefully less dangerous).
So how much shock current will flow through the girl’s body if the potential difference is 240 volts (assuming 240 – 0 volts)?
That will depend on how much resistance is presented by the girl’s body against current flow from the live wire and the neutral wire.
So how much is the normal body resistance? This is actually Question No 3 above.
Well, when the skin is dry, the body can present a resistance as high as 100,000 ohms (that is 100 kilo-ohms) against the current flow.
The magnitude of current is lower as the body resistance goes higher. So in this case, the magnitude of the shock current will be:
Shock current = voltage difference divided by body resistance
= 240 volt / 100,000 ohm
= 0.0024 ampere
That is 2.4 thousandth of an ampere of electric current flow, or 2.4 mili-amperes, or 2.4 mA.
How much damage will this amount of current do to the human body? Again you can see the detail list of the injuries in the above-mentioned post. However I listed a few of them here for easy comparison and to help you appreciate the size of this shock current from the viewpoint of injuries that it can cause.
At 1 mA – a normal person would feel a slight tingling sensation.
At 5 mA - A light shock will be felt, but most persons will be able to “let go”. Not a painful feeling, but definitely disturbing. However, a strong reflexive movement by the victim can cause further accidents and other type of injuries.
At 6 to 30 mA - The victim can be paralyzed, or the muscles will freeze (will not be able to release a tool, wire, or other object).
Painful, and my not be possible to let go.
At high voltage (above 600 Volt), this current can already cause severe burns.
As you can see above, at 5 mili-amperes or below, a normal person should still be able to let go the electrified object the he accidentally came into contact with. So a person with dry skin would be less likely to suffer severe injuries if he accidentally comes into contact with a 240 volts live wire. A 110 volts domestic voltage at American house will be less than half of that shock current, so it would be safer theoretically (the American safety follows a different standard so we cannot really compare them apple to apple).
Now let’s see what will happen when the skin is wet. The wet condition can result in a very much lower skin resistance to electric shock current. It can be as low as 1,000 ohms. Therefore the shock current is
Shock current = 240 divided 1000
= 0.24 ampere, which is 240 mili amperes!
From the list that I copied above, at 30 mA the victim would surely not be able to let go of the electrified object he was holding. Therefore the shock current through the body will eventually rise to the maximum that is limited by the body resistance which is 240 mA.
So the victim can suffer a maximum level of injuries. The list on the other post says:
(At 75 mili-Amperes and above – The victim undergo ventricular fibrillation (very rapid, ineffective heartbeat). This condition can cause death within a few minutes. The only way to save the victim is by a special device called defibrillator.
So there you have it. The comparison of the level of resulting injuries between the lowest and the highest skin contact resistances.
BASIC CASES OF ELECTRIC SHOCKS
I started out this post with the intention of explaining about how someone can get electric shocks. But I seem to have spent this far explaining more on the logics of electric shocks.
However, the understanding of the working principles, or the mechanics, behind these accidents will be more useful to you in achieving the most important objective: that is to prevent all serious injuries that result from electrical shocks.
It would be nice to be able to prevent electrical accidents altogether. However as any construction man would testify, it is near to impossible to prevent accidents at construction sites.
The rough environment that a temporary electrical installation is subjected to, the nature of the electrical users at the jobsite, and the difficulties faced by persons responsible on electrical safety on large construction sites to ensure adequate level of safety habits are actually practiced throughout the construction grounds and floors. These three constraints make it near impossible to totally prevent electrical accidents on large construction sites with thousands of workers, especially those with small site areas such as high rise construction at city centers.
What we can do is to minimize the degree of electrical injuries when they do occur.
However, electrical accidents at home or office can still be prevented totally. That is my opinion.
Now THE how to get electric shock No 1. As shown in Diagram 1 at high up in the beginning of this post, that can happen when two locations on the human body came into contact with conductive parts at two different voltages. I have used this diagram to explain the whole upper part of this post above. So that should be enough.
Diagram 2 -Touching live and earth wire
In this case, the right hand came into contact with the earth wire instead of the neutral wire shown in Diagram 1. The result can be similar. I said “can be” instead of “will be”. Why? Because in this case, the live red wire can be installed with an electric shock protection device that will sense this shock current.
The devise is the ELCB (earth leakage circuit breaker). Other names are also used to explain this function in an electrical installation such as RCD (residual current devices), GFCI (ground fault circuit interrupters), etc. Read this post ELCB Circuit to know more how this device functions.
Diagram 3 – When the hand touches a live wire and the person is not separated at the feet from the ground with purpose-made electrical insulation means like rubber shoes, the rubber mat in front of the switchboards in electrical rooms, etc.
Diagram 4 – When there is simultaneous contacts with fault electric motors and ground.
The electric motor can be any electric equipment or appliances. The same process of electric shock current flow will happen.
There are more points that I wish to write down here. However it’s already almost three AM and I have to go to work tomorrow. So I will continue this some other time, in another post.
Stay safe. Electricity kills.
RELATED ARTICLES: a) Home electrical wiring, symbols and checking;
Copyright http://electricalinstallationblog.blogspot.com/ How you get electric shocks
How to build your own electric cars
Why would I want to send a post on how to build your own electric cars on this blog?
Many technological development’s major leaps occurred as a product of some crises, wars or military competition. The internet, the space exploration (and therefore the technological byproducts that they created), the stealth fighter jets, and so many others that I need to dig back into my old books to write them all here. These progresses can be said to have happened because of the pressures from the environment at that time.
So, what relation does this have with electric cars and the title of this blog, Electrical Installations? A lot actually.
The technology that makes up an electric car system has been around a long time. I am not sure how long. By a blind guess, I would say 20 years or more. Please correct me if I am wrong here.
However, who cares for electric cars?
Why should we care for this “old” technology now?
We should care because a new global crisis has started; not just one crisis but two crises are coming up fast simultaneously – the global warming and the energy crises. Both of these are global crises and in this interconnected world, all peoples of this world will have to suffer the consequences.
Everybody must be concerned and everybody should do what he or she can. If we don’t do what we can, then how can we expect the world’s government to do what they can in order to contain this crises?
Automobiles are one of the contributors to the global warming. We can debate on how many percent are contributed by these machines, but where the emissions can be shut off, we should do it without talking too much. That is how to get things done.
We are lucky because the electric car technology has already been here a long time. This can help us shut down the car emissions fast. In my opinion, this is something that everybody can easily do.
I have always considered cars and trucks as among the mechanical machines. However, with these crises coming closer and the electric car technology getting more popular, I think now these machines should be in the domain of electricians and electrical engineers.
For this reason I have decided to expand the scope of this blog to cover the electric car technology and also the related alternative forms of electricity producing machines such as the solar panels and the wind-powered electric generators.
Therefore, from today on you can also read some articles on solar electrical installations and wind-powered electrical plants on this blog.
With that said, I am going to end this post by pointing out to the readers where you can get the reading materials and step-by-step instructions on how to build your own electric cars.
Click on the link and see what the advertiser have to say. You have nothing to lose. Advertisers’ online landing pages are always full of information even though you still have to filter out the ridiculous claims when you see them. Ridiculous claims or not, we still have to buy cars so we can go to work.
See you in the next post.
Copyright http://electricalinstallationblog.blogspot.com/ How to build your own electric cars
Many technological development’s major leaps occurred as a product of some crises, wars or military competition. The internet, the space exploration (and therefore the technological byproducts that they created), the stealth fighter jets, and so many others that I need to dig back into my old books to write them all here. These progresses can be said to have happened because of the pressures from the environment at that time.
So, what relation does this have with electric cars and the title of this blog, Electrical Installations? A lot actually.
The technology that makes up an electric car system has been around a long time. I am not sure how long. By a blind guess, I would say 20 years or more. Please correct me if I am wrong here.
However, who cares for electric cars?
Why should we care for this “old” technology now?
We should care because a new global crisis has started; not just one crisis but two crises are coming up fast simultaneously – the global warming and the energy crises. Both of these are global crises and in this interconnected world, all peoples of this world will have to suffer the consequences.
Everybody must be concerned and everybody should do what he or she can. If we don’t do what we can, then how can we expect the world’s government to do what they can in order to contain this crises?
Automobiles are one of the contributors to the global warming. We can debate on how many percent are contributed by these machines, but where the emissions can be shut off, we should do it without talking too much. That is how to get things done.
We are lucky because the electric car technology has already been here a long time. This can help us shut down the car emissions fast. In my opinion, this is something that everybody can easily do.
I have always considered cars and trucks as among the mechanical machines. However, with these crises coming closer and the electric car technology getting more popular, I think now these machines should be in the domain of electricians and electrical engineers.
For this reason I have decided to expand the scope of this blog to cover the electric car technology and also the related alternative forms of electricity producing machines such as the solar panels and the wind-powered electric generators.
Therefore, from today on you can also read some articles on solar electrical installations and wind-powered electrical plants on this blog.
With that said, I am going to end this post by pointing out to the readers where you can get the reading materials and step-by-step instructions on how to build your own electric cars.
Click on the link and see what the advertiser have to say. You have nothing to lose. Advertisers’ online landing pages are always full of information even though you still have to filter out the ridiculous claims when you see them. Ridiculous claims or not, we still have to buy cars so we can go to work.
See you in the next post.
Copyright http://electricalinstallationblog.blogspot.com/ How to build your own electric cars
Tuesday, January 5, 2010
Electrical injury pictures
I found these pictures of electrical injuries from one of the NIOSH websites. They were classified as in public domain and free for re-publishing. So I put them here for those who need them but have no time or the internet skills to go around digging inside those massive websites themselves.
How did these injuries occur? How did it happen? Visit this post, How you get electric shocks. I have made a few simple diagrams and easy to understand descriptions of the mechanics that can lead to these sort of electrical injuries.
Picture 1 - Entrance Wound
When electric shock happens, the current enter the body at one point and then leave the body at another point of contact. So there are two points of the body where there are electrical contact happens to complete the electrical circuit that will allow the shock current to flow through.
At each of the points of contact there is resistance. The human body itself also presents resistance but this normally very low compared to the resistances at the two points of contact. Because of these resistances, the flow of the shock current is converted into heat at these two locations which can cause severe burns.
What the image in Picture 1 shows is the burn injury on the body at the location where the shock current flows in. The dark spot in the center of the wound is the entrance point. This man was lucky. The shock current narrowly missed his spinal cord.
Picture 2 shows the injuries where the current leaves the body. Usually this is under the feet where they touch the ground. The magnitude of the current when it enters the body is the same as when it leaves the body. If both feet touch the ground at the moment of the shock, then it is the total of the exiting currents at both feet.
In the case of Picture 2, it didn’t say whether or not both feet were injured. The foot shown here suffered massive internal injuries that is not visible in the picture here. However it was so bad that the foot had to be amputated a few days later.
Picture 2 – Exit wound
Picture 3 – Arc or flash burn
Don’t be there if you are not supposed to be there. That is what we usually say to bystanders who are waiting to witness the Energization of a newly completed electrical system. It is always dangerous to be anywhere near the place because one of the most common types of accident there is electrical explosions.
The image in Picture 3 is one example of injuries from electrical explosions. The NIOSH site said that man was near an electrical panel when the accident happened. He did not touch the electrical panel.
However the electricity arched through the air. An example of electric arcs through the air is what we call lightning strikes. Surprised? So you can consider this an injury from an extremely small lightning strike.
The man happened to be in the path of the arcing electrical current, so the current punched into his body. You may wonder why the injury is located at the armpit. That is because there were perspiration on his body at the time and perspirations are very conductive. So his armpit presented a very conductive (and therefore “very attractive”) path for the electric arc current.
Picture 4 - Thermal Contact Burns
Electric current not only heats up electrical wires that burn houses. If and when it travels through a human body, the points of contact where it enters and leaves the body can generate enough heat (due to skin contact resistances) to cause fire and burns the victim’s clothes.
That was what happened to the victim in this picture. The current exited the victim’s body at the knee. It caused fire at the skin there which then catches his clothing and burned his upper leg.
Picture 5 – Internal injuries
This is an example of an electric tool accident. The worker was shocked by the electric tool he was holding. You can see from the picture the thermal burn injury at the entry point of the shock current.
However the wound was even more severe that what can be seen here. Massive internal tissue damages have occurred that subsequently caused severe swelling to the hand.
The swelling usually peaks 24 – 72 hours after the electric shock. In this case, the hospital needed to cut open the skin on the arm in order to relieve the pressure that resulted from the swelling which could have damaged nerves and blood vessels. This image in Picture 6 below was after the skin was cut open a few days later.
Picture 6 – A few days later
Picture 7 - Involuntary Muscle Contraction
This worker was working above overhead electrical cables. For some reasons he fell and grabbed the bare cables in order to save himself. The resulting electric shock mummified his first two fingers, which later had to be removed.
The acute angle of the wrist was caused by the burning of the tendons, which had contracted, drawing the hand with them.
That is all I have the time for today. I wish I could write more on these pictures but that will have to wait until some other time.
You can see a number of pictures I uploaded on electrical installations that could have caused these sorts of accidents. See this post, Temporary electrical installations. There are some lessons to be learned.
How much current does it take to cause the kind of injuries that you see in the above pictures? Read my other post, ELCB - Home Electric Shock Protection, to know them in details.
See you again.
Copyright http://electricalinstallationblog.blogspot.com/ - Electrical injury pictures
How did these injuries occur? How did it happen? Visit this post, How you get electric shocks. I have made a few simple diagrams and easy to understand descriptions of the mechanics that can lead to these sort of electrical injuries.
Picture 1 - Entrance Wound
When electric shock happens, the current enter the body at one point and then leave the body at another point of contact. So there are two points of the body where there are electrical contact happens to complete the electrical circuit that will allow the shock current to flow through.
At each of the points of contact there is resistance. The human body itself also presents resistance but this normally very low compared to the resistances at the two points of contact. Because of these resistances, the flow of the shock current is converted into heat at these two locations which can cause severe burns.
What the image in Picture 1 shows is the burn injury on the body at the location where the shock current flows in. The dark spot in the center of the wound is the entrance point. This man was lucky. The shock current narrowly missed his spinal cord.
Picture 2 shows the injuries where the current leaves the body. Usually this is under the feet where they touch the ground. The magnitude of the current when it enters the body is the same as when it leaves the body. If both feet touch the ground at the moment of the shock, then it is the total of the exiting currents at both feet.
In the case of Picture 2, it didn’t say whether or not both feet were injured. The foot shown here suffered massive internal injuries that is not visible in the picture here. However it was so bad that the foot had to be amputated a few days later.
Picture 2 – Exit wound
Picture 3 – Arc or flash burn
Don’t be there if you are not supposed to be there. That is what we usually say to bystanders who are waiting to witness the Energization of a newly completed electrical system. It is always dangerous to be anywhere near the place because one of the most common types of accident there is electrical explosions.
The image in Picture 3 is one example of injuries from electrical explosions. The NIOSH site said that man was near an electrical panel when the accident happened. He did not touch the electrical panel.
However the electricity arched through the air. An example of electric arcs through the air is what we call lightning strikes. Surprised? So you can consider this an injury from an extremely small lightning strike.
The man happened to be in the path of the arcing electrical current, so the current punched into his body. You may wonder why the injury is located at the armpit. That is because there were perspiration on his body at the time and perspirations are very conductive. So his armpit presented a very conductive (and therefore “very attractive”) path for the electric arc current.
Picture 4 - Thermal Contact Burns
Electric current not only heats up electrical wires that burn houses. If and when it travels through a human body, the points of contact where it enters and leaves the body can generate enough heat (due to skin contact resistances) to cause fire and burns the victim’s clothes.
That was what happened to the victim in this picture. The current exited the victim’s body at the knee. It caused fire at the skin there which then catches his clothing and burned his upper leg.
Picture 5 – Internal injuries
This is an example of an electric tool accident. The worker was shocked by the electric tool he was holding. You can see from the picture the thermal burn injury at the entry point of the shock current.
However the wound was even more severe that what can be seen here. Massive internal tissue damages have occurred that subsequently caused severe swelling to the hand.
The swelling usually peaks 24 – 72 hours after the electric shock. In this case, the hospital needed to cut open the skin on the arm in order to relieve the pressure that resulted from the swelling which could have damaged nerves and blood vessels. This image in Picture 6 below was after the skin was cut open a few days later.
Picture 6 – A few days later
Picture 7 - Involuntary Muscle Contraction
This worker was working above overhead electrical cables. For some reasons he fell and grabbed the bare cables in order to save himself. The resulting electric shock mummified his first two fingers, which later had to be removed.
The acute angle of the wrist was caused by the burning of the tendons, which had contracted, drawing the hand with them.
That is all I have the time for today. I wish I could write more on these pictures but that will have to wait until some other time.
You can see a number of pictures I uploaded on electrical installations that could have caused these sorts of accidents. See this post, Temporary electrical installations. There are some lessons to be learned.
How much current does it take to cause the kind of injuries that you see in the above pictures? Read my other post, ELCB - Home Electric Shock Protection, to know them in details.
See you again.
Copyright http://electricalinstallationblog.blogspot.com/ - Electrical injury pictures
Friday, January 1, 2010
Hospital LV electrical installation
The low voltage (LV) electrical installation for a hospital is designed based on the size and complexities of the hospital to be constructed. A small hospital would only require simpler design similar to other types of electrical works in buildings.
However for large hospitals, or hospitals with sophisticated equipment to be installed, the electrical installation will become more complex because of the wide variety of functions that is provided in the hospital. This ranges from industrial requirements, specialized medical departments, nurses’ hostels, staff accommodation areas, operating theaters and laboratories.
Specials requirements of a hospital electrical design
A hospital deals with life and death of patients. Therefore there are special requirements that must be met by the electrical installation. The most important of these is probably the reliability of the electrical system that is being designed. Many patients rely on life saving equipment and procedures just to stay alive. Therefore, power supply failures longer than certain duration cannot be accepted. Some of the equipment cannot even tolerate a power interruption any more than a few seconds.
All these means that a hospital electrical installation needs to be designed with not just a reliable electrical system, but also with a highly dependable backup electric supply sources. The fact that the power supply to some equipment cannot even be interrupted for any longer than just a few seconds means that an Interruptible Power Supply (UPS) system is an absolute necessity.
Hospital’s electrical installation write-up below
The following is a write-up on the low voltage (LV) electrical installation for a 500-bed government hospital. I modified it from part of an early draft that I did for a turnkey proposal a few years ago. I did not include the high voltage part of the installation here because the treatment on a HV system will best be handled on its own in a separate post.
You may notice that I have managed to give more explanations in certain sections, while the others are very short. I will get back into these short sections when I can steal a little bit more time from my work to finish them.
A LITTLE MESSAGE FROM THE SPONSOR
After reading this post, if you can spare the time, check out the following link. It is a link on how to convert your car into an electric car at minimal cost. It is a way we in the electrical industry can contribute in the global effort to save this planet . In any case, it can save some significant dollars from our daily transport costs. Check it out. It’s a good reading.
A. Distribution system
Usually the major load centers of a large hospital would consist of the Hospital Complex, the Mechanical Plant, and the accommodation areas which are the Nurses’ Hostels and the Staff Quarters.
1. Accommodation area substation
The nurses’ hostels and the staff quarters are usually mentioned separately because the each unit of the staff quarters would be provided with a separate individual meter installed by the electric supply authority. The occupants will need to pay for the electricity bill themselves.
While the electricity cost of all the nurses hostels would be part of the bulk electricity bill charged by the supply company to the hospital. The nurses’ do not have to pay for the bill themselves. This is usually the arrangement made by government hospitals. Private hospitals may have different arrangements. However, the separately billed electric meters of the staff quarters are a standard practice at all hospitals as far as I know.
This separately billed meters for the staff quarters may seem a trivial issue, but from the design of the electrical distribution, in many cases this has made the design of the distribution system at the accommodation area more complicated.
I may dedicate a post in future just to discuss this topic, but for now I will not go further because that can distract us from the overall distribution system of the hospital electrical installation.
2. Mechanical plant substation
The mechanical plant is actually not just for the mechanical systems. It is generally a separate building that houses the central plants for almost all major mechanical and electrical services at the hospital complex. The maximum load current drawn by these plants are usually very large, therefore there require large switchgears, equipment and rooms needed to house them.
The mechanical plants for large hospitals are also massive in terms of physical sizes (for example, the chilled water system for the air-conditioning, the cooling towers, fire protection pumps and water tanks, etc). The machines and equipment at each of these plants can also be relatively noisy even during normal operation.
All these and the need for proper design to allow for easy maintenance require that a separate and dedicated plant building be allocated. A dedicated electrical substation is usually provided to handle all the loads inside the mechanical plant building.
3. Hospital complex substation
Many equipment inside the hospital complex require very large current and also very low impedance.
As the mechanical plant building is usually a distance away from the main hospital complex, a significant voltage drop is difficult to avoid if the supply center is located there. The low voltage cables needed to overcome this will be unnecessarily large and difficult to maneuver along the cable route. Not to mention the cost of these unnecessarily large low voltage cables and their support system.
Apart from that, some equipment such as the X-ray machines require very low impedance for proper operation.
These factors means that the substation (i.e. Hospital Substation) needed to supply the electrical loads inside the main hospital complex must be located close the local load center, which is inside the main hospital building itself. Feeder cables are looped to the Hospital Substation from the Mechanical Plant Substation at high voltage (usually at 11 kV).
How is the distribution system designed to make it reliable?
As the reliability of the electrical supply in a hospital can make a difference between life and death of some patients, an elaborate design effort is usually given to achieve this objective.
Foremost of all, the supply authority is usually requested to provide two incoming feeders to the hospital site. The purpose is so that if one incoming fails, the supply for the full load can be fed through the other feeder. Needless to say, these are high voltage feeders (usually 11 kV). Under normal operation, both feeders are usually in operation with each feeder supplying half of the load generally.
Some clients go as far as requiring that each of the high voltage feeders must not come from the same supply source in the authority’s local distribution network. This is to further reduce the downtime of incoming supply which some local distribution networks can fulfill and some not able to do so due to the limitations of their existing local distribution network.
Busbar couplers increase the electric supply reliability
In order to provide further flexibility, and therefore reliability, the arrangement of the busbars can be designed with a little bit more sophistication. For example, by providing separate busbars at suitable sections of a distribution center (e. the main switchboards, the downstream sub-switchboards, the standby diesel generator panels, the distribution board busbars, etc), the various sections of the busbars can be coupled with a switching system to direct the electric supply via alternative routes to critical areas and machines.
Reliability increased by the choice of distribution cables
The choice of the types of cables used in the distribution can also be used to increase reliability. The mineral insulated (MICC) cables give an added advantage of being a comparatively low impedance cable for a given size compared with other types of cables. This is a particularly important requirement for a supply to x-ray machines.
Use metal-clad busducts where possible
The metal enclosed busducts can also give significant further improvements because of its flexibility in allowing additional tappings at any point along the supply route without reducing the reliability of the supply feeder. Other types of cables would require an elaborate work and workmanship to provide the additional tappings, which can further reduce the reliability in the long run. It has been an established fact that many of faults on low voltage distribution feeders develop from these tapping locations.
A hospital’s backup power supply sources.
The strategies shown above on how to provide flexibility to the electrical distribution system will not deliver the reliability of the electric supply that it intends to if the causes of power failures come from the source of the supply, which is the authority’s local distribution network.
A hospital cannot take this chance. That is why a system of standby power supply sources are always designed for in the electrical installation of a hospital especially the large ones.
The standby power is used to allow the hospital to keep running its essential services during the mains fail. Normally fifty percent of the general lighting at the main hospital complex would be connected to the essential supply circuit so the light level is reduced to fifty percent. However this lighting level is still sufficient to allow the hospital to operate normally on a temporary basis.
Which socket outlets are connected to the hospital’s essential supply?
How many and which socket outlets (and other power points) are connected to the essential circuit are usually decided on a project to project basis. Normally during the design stages, the end users of the hospital being designed, which are usually the future staff for each department, would be called in for sessions of technical interaction with the hospital designers, architect and engineers.
In these sessions, the need of the users would be captured and incorporated into the design. These types of sessions can take thousands of hours for large hospitals. They are also highly technical and stressing sessions with parties from all sides clashing (I mean that in the construction management terms) with one another in trying to bring all the conflicting objectives to a compromise so that the designers can give a practical solution in the form of a design that can be built within the cost allocated.
Mechanical and electrical services for a hospital construction can easily come to 30 percent of the total construction cost. This does not yet include the cost of medical equipment and the IT system.
Sorry for the digression.
Similar to the power socket outlets, the air conditioning loads connected to the essential circuit are also usually decided on project to project basis with the aid of the information gathered during the interaction sessions described above.
Usually the central air conditioning system for a large hospital is provided with a smaller chiller (some people like to call it “baby chiller”). This chiller unit is chosen from a smaller capacity and it des not run during daytime operation. It will supply the load of the air conditioning system during very low load such as after midnight. Some machines may need to be air-conditioned 24 hors a day so the spaces housing these machines are supplied by the baby chiller during the low load periods. Therefore, this baby chiller may also be required to be connected to the essential supply circuit.
THE backup supply sources
These backup sources are almost always in the form of standby diesel automatic generators. These generators are usually located away from the main hospital building due to the level of noise produced during their operation. That is one of the reasons for a separate building to house the mechanical and electrical plants. So the “standby gensets” (another common words used to call this equipment) are housed inside the Mechanical Plant.
Uninterruptible Power Supply (UPS) System
As mentioned above, some equipment in the hospital cannot tolerate power supply failures at all when they are in use. So they are connected to the UPS system. The UPS system is in turn connected to the essential supply circuit, which is backed up by the standby generators.
One important point need to be noted with regards to the standby electrical generators. These generators are installed to fulfill two requirements. One is the operation requirements of the hospital which need some services to keep operating in the even of mains power failure. The other reason is the requirements of the Fire Department that some the fire system is fully operational in the event a fire case occurs during the absence of the mains supply which include also some lighting for evacuation purposes.
The Fire Department requirements on the standby electric generators
The Fire Department usually requires that the standby generators be up and supplying load within a few seconds (within 15 seconds the last time I checked, if I remember it correctly. This number may vary slightly from country to country.) from the moment of mains failure. However in practice, some generators in some installations are up to this performance. It can take longer.
Even with 15 second blackout, some works in the hospital may be disrupted long enough to cause danger to patients. The prime examples are the procedures in the operation theatres (OT) and the patients who are continuously dependent on some live-saving machines.
The UPS batteries
Therefore the UPS system is installed to fill this 15-second gap. The batteries in the UPS system will be supplying power only for this 15-second period plus a few seconds more added inside the UPS system settings to make sure the electrical supply (the mains supply or the standby generator’s supply) is stable before the UPS storage batteries are switched out of the supply circuit (and back into the charging circuit).
That was the case when the standby generator is up and running within 15 seconds. What if it takes longer (never mind the fire regulations regarding this)? What if the generator actually fails to start? In can happen, and it does happen, as the case when the starting batteries fail to supply sufficient voltage after a few years because of negligence by the maintenance team.
I purposely drag this point longer just to emphasize it, just to stress on the critical function served by the UPS in the backup electric supply system of a hospital.
More points on the distribution system (which I will elaborate further soon)
1. A substation’s low voltage section consists of the Main Switchboard (MSB), the Essential Main Switchboard (EMSB) and a bus coupler. The EMSB board supplies the required essential lighting, power and critical equipment in the Hospital Complex. Part of it also will serve the mechanical load such as air condition, compressed air, vacuum system, and boiler and fire protection system.
2. Local UPS will be provided to support the emergency power requirements of critical loads.
3. The normal, essential and emergency supplies will have separate main switchboard, sub-switchboard and distribution board to supply the respective lighting, power and mechanical services.
4. All switchboards and distribution boards will be provided with suitable types of protection. The sheet metal materials of the board enclosures will be of electro-galvanized type.
5. The design will provide at least 20% spare capacities in all switchboard and distribution boards for future needs, while the main switchboards will be provided with a spare capacity of 30 percent. The main switchboard of the hospital complex will be installed with an automatic power factor board and capacitor bank to keep power factor of the installation at not less than 0.85 lagging in any load condition.
6. A power monitoring system will be installed at the incomers. They will monitor the incomers for all the important electrical parameters including harmonic and also load shedding of non-essential loads. It will also be able to communicate with remote stations by any microprocessor.
7. One bulk electricity meter is provided for the hospital complex including the staff accommodation buildings. Separate meters will be provided for the retail spaces, the cafeteria, canteen, kitchen area, staff quarters and any other spaces for hospital functions that are planned for privatization by the hospital management.
However, as the detailed design develops, a separate bulk meter taking a supply at low voltage from the authority may be provided for the staff quarters, nurses’ hostels and housemen mess.
The reason being the limit set by the authority that any new site with load demand bigger than 5 MVA are required to surrender an empty 100 feet by 100 feet substation space for a future 33/11 kV substation.
At present, the estimated maximum demand for the whole complex including the accommodation area is 5.5 MVA, which has exceeded the % MVA limit.
As the detailed design is developed deeper, in tandem with the gradually more information available on the end-user requirements from the Client-Contractor interaction sessions, the expected maximum demand may be trimmed to below 5 MVA.
If it cannot be trimmed down to below 5 MVA, the application of supply that will be submitted to the electric supply authority will request two bulk meters: one HV bulk meter for 4.8 MVA that will supply both the Hospital Substation and the Mechanical Plant Substation.
The other will be an LV bulk meter for 700 kVA at the Accommodation area Substation which will provide supply to all the accommodation buildings.
Many times the authority approved this arrangement. However, there have also been cases where these types of arrangement were rejected.
B. Cabling and wiring
1. Normal, essential and emergency circuits should be installed in separate trunking and conduits. They need all be properly labeled.
2. All cabling and wiring should be in G.I. conduit. All trunking / tray / ladders shall be of unpainted electro-galvanized sheet metal and marked with proper a color coding system.
C. Electrical socket outlets
Minimum two 13A switched socket outlets should be provided for each bed in the normal wards whereby one of them is connected to essential supply.
Isolators should be provided to suffice the requirement of all equipment.
D. Fans
1. In buildings or rooms where air-conditioning is not provided such as at certain selected wards and at the residential buildings, fans should be installed as required.
2. The sweep fans provided should be complete with speed controls, located at the entry door.
E. Lighting installation
1. A hospital is a very complex, task-intensive institution. The selection of lighting services and control gears should be on the basis of functional aspects, energy efficient, good color rendition and low maintenance.
2. The lighting for various areas should be designed in the compliance with IES, DHSS and current Work Ministry’s code of practice to achieve the average illumination levels as described in attached schedule (will be uploaded later).
3. Labor room, Procedure room, Autopsy room and Treatment room should have the ceiling mounted examination light 0f 30000 lux.
Electrical HV switchgear installation pictures for hospitals
Below you may find some pictures (Well, only one for now.) on electrical installation in hospitals. I may upload more of them in future when I come back to finish on the short sections remaining in this post. So stay tuned.
P/S: You can also see quite a number of electrical installation pictures that I have uploaded at this post: Temporary electrical installations
Picture 1 - Hospital HV switchgear installation in progress
Picture 2 - HV switchgear installation - Rear view
Copyright http://electricalinstallationblog.blogspot.com/ - Hospital LV electrical installation
However for large hospitals, or hospitals with sophisticated equipment to be installed, the electrical installation will become more complex because of the wide variety of functions that is provided in the hospital. This ranges from industrial requirements, specialized medical departments, nurses’ hostels, staff accommodation areas, operating theaters and laboratories.
Specials requirements of a hospital electrical design
A hospital deals with life and death of patients. Therefore there are special requirements that must be met by the electrical installation. The most important of these is probably the reliability of the electrical system that is being designed. Many patients rely on life saving equipment and procedures just to stay alive. Therefore, power supply failures longer than certain duration cannot be accepted. Some of the equipment cannot even tolerate a power interruption any more than a few seconds.
All these means that a hospital electrical installation needs to be designed with not just a reliable electrical system, but also with a highly dependable backup electric supply sources. The fact that the power supply to some equipment cannot even be interrupted for any longer than just a few seconds means that an Interruptible Power Supply (UPS) system is an absolute necessity.
Hospital’s electrical installation write-up below
The following is a write-up on the low voltage (LV) electrical installation for a 500-bed government hospital. I modified it from part of an early draft that I did for a turnkey proposal a few years ago. I did not include the high voltage part of the installation here because the treatment on a HV system will best be handled on its own in a separate post.
You may notice that I have managed to give more explanations in certain sections, while the others are very short. I will get back into these short sections when I can steal a little bit more time from my work to finish them.
A LITTLE MESSAGE FROM THE SPONSOR
After reading this post, if you can spare the time, check out the following link. It is a link on how to convert your car into an electric car at minimal cost. It is a way we in the electrical industry can contribute in the global effort to save this planet . In any case, it can save some significant dollars from our daily transport costs. Check it out. It’s a good reading.
A. Distribution system
Usually the major load centers of a large hospital would consist of the Hospital Complex, the Mechanical Plant, and the accommodation areas which are the Nurses’ Hostels and the Staff Quarters.
1. Accommodation area substation
The nurses’ hostels and the staff quarters are usually mentioned separately because the each unit of the staff quarters would be provided with a separate individual meter installed by the electric supply authority. The occupants will need to pay for the electricity bill themselves.
While the electricity cost of all the nurses hostels would be part of the bulk electricity bill charged by the supply company to the hospital. The nurses’ do not have to pay for the bill themselves. This is usually the arrangement made by government hospitals. Private hospitals may have different arrangements. However, the separately billed electric meters of the staff quarters are a standard practice at all hospitals as far as I know.
This separately billed meters for the staff quarters may seem a trivial issue, but from the design of the electrical distribution, in many cases this has made the design of the distribution system at the accommodation area more complicated.
I may dedicate a post in future just to discuss this topic, but for now I will not go further because that can distract us from the overall distribution system of the hospital electrical installation.
2. Mechanical plant substation
The mechanical plant is actually not just for the mechanical systems. It is generally a separate building that houses the central plants for almost all major mechanical and electrical services at the hospital complex. The maximum load current drawn by these plants are usually very large, therefore there require large switchgears, equipment and rooms needed to house them.
The mechanical plants for large hospitals are also massive in terms of physical sizes (for example, the chilled water system for the air-conditioning, the cooling towers, fire protection pumps and water tanks, etc). The machines and equipment at each of these plants can also be relatively noisy even during normal operation.
All these and the need for proper design to allow for easy maintenance require that a separate and dedicated plant building be allocated. A dedicated electrical substation is usually provided to handle all the loads inside the mechanical plant building.
3. Hospital complex substation
Many equipment inside the hospital complex require very large current and also very low impedance.
As the mechanical plant building is usually a distance away from the main hospital complex, a significant voltage drop is difficult to avoid if the supply center is located there. The low voltage cables needed to overcome this will be unnecessarily large and difficult to maneuver along the cable route. Not to mention the cost of these unnecessarily large low voltage cables and their support system.
Apart from that, some equipment such as the X-ray machines require very low impedance for proper operation.
These factors means that the substation (i.e. Hospital Substation) needed to supply the electrical loads inside the main hospital complex must be located close the local load center, which is inside the main hospital building itself. Feeder cables are looped to the Hospital Substation from the Mechanical Plant Substation at high voltage (usually at 11 kV).
How is the distribution system designed to make it reliable?
As the reliability of the electrical supply in a hospital can make a difference between life and death of some patients, an elaborate design effort is usually given to achieve this objective.
Foremost of all, the supply authority is usually requested to provide two incoming feeders to the hospital site. The purpose is so that if one incoming fails, the supply for the full load can be fed through the other feeder. Needless to say, these are high voltage feeders (usually 11 kV). Under normal operation, both feeders are usually in operation with each feeder supplying half of the load generally.
Some clients go as far as requiring that each of the high voltage feeders must not come from the same supply source in the authority’s local distribution network. This is to further reduce the downtime of incoming supply which some local distribution networks can fulfill and some not able to do so due to the limitations of their existing local distribution network.
Busbar couplers increase the electric supply reliability
In order to provide further flexibility, and therefore reliability, the arrangement of the busbars can be designed with a little bit more sophistication. For example, by providing separate busbars at suitable sections of a distribution center (e. the main switchboards, the downstream sub-switchboards, the standby diesel generator panels, the distribution board busbars, etc), the various sections of the busbars can be coupled with a switching system to direct the electric supply via alternative routes to critical areas and machines.
Reliability increased by the choice of distribution cables
The choice of the types of cables used in the distribution can also be used to increase reliability. The mineral insulated (MICC) cables give an added advantage of being a comparatively low impedance cable for a given size compared with other types of cables. This is a particularly important requirement for a supply to x-ray machines.
Use metal-clad busducts where possible
The metal enclosed busducts can also give significant further improvements because of its flexibility in allowing additional tappings at any point along the supply route without reducing the reliability of the supply feeder. Other types of cables would require an elaborate work and workmanship to provide the additional tappings, which can further reduce the reliability in the long run. It has been an established fact that many of faults on low voltage distribution feeders develop from these tapping locations.
A hospital’s backup power supply sources.
The strategies shown above on how to provide flexibility to the electrical distribution system will not deliver the reliability of the electric supply that it intends to if the causes of power failures come from the source of the supply, which is the authority’s local distribution network.
A hospital cannot take this chance. That is why a system of standby power supply sources are always designed for in the electrical installation of a hospital especially the large ones.
The standby power is used to allow the hospital to keep running its essential services during the mains fail. Normally fifty percent of the general lighting at the main hospital complex would be connected to the essential supply circuit so the light level is reduced to fifty percent. However this lighting level is still sufficient to allow the hospital to operate normally on a temporary basis.
Which socket outlets are connected to the hospital’s essential supply?
How many and which socket outlets (and other power points) are connected to the essential circuit are usually decided on a project to project basis. Normally during the design stages, the end users of the hospital being designed, which are usually the future staff for each department, would be called in for sessions of technical interaction with the hospital designers, architect and engineers.
In these sessions, the need of the users would be captured and incorporated into the design. These types of sessions can take thousands of hours for large hospitals. They are also highly technical and stressing sessions with parties from all sides clashing (I mean that in the construction management terms) with one another in trying to bring all the conflicting objectives to a compromise so that the designers can give a practical solution in the form of a design that can be built within the cost allocated.
Mechanical and electrical services for a hospital construction can easily come to 30 percent of the total construction cost. This does not yet include the cost of medical equipment and the IT system.
Sorry for the digression.
Similar to the power socket outlets, the air conditioning loads connected to the essential circuit are also usually decided on project to project basis with the aid of the information gathered during the interaction sessions described above.
Usually the central air conditioning system for a large hospital is provided with a smaller chiller (some people like to call it “baby chiller”). This chiller unit is chosen from a smaller capacity and it des not run during daytime operation. It will supply the load of the air conditioning system during very low load such as after midnight. Some machines may need to be air-conditioned 24 hors a day so the spaces housing these machines are supplied by the baby chiller during the low load periods. Therefore, this baby chiller may also be required to be connected to the essential supply circuit.
THE backup supply sources
These backup sources are almost always in the form of standby diesel automatic generators. These generators are usually located away from the main hospital building due to the level of noise produced during their operation. That is one of the reasons for a separate building to house the mechanical and electrical plants. So the “standby gensets” (another common words used to call this equipment) are housed inside the Mechanical Plant.
Uninterruptible Power Supply (UPS) System
As mentioned above, some equipment in the hospital cannot tolerate power supply failures at all when they are in use. So they are connected to the UPS system. The UPS system is in turn connected to the essential supply circuit, which is backed up by the standby generators.
One important point need to be noted with regards to the standby electrical generators. These generators are installed to fulfill two requirements. One is the operation requirements of the hospital which need some services to keep operating in the even of mains power failure. The other reason is the requirements of the Fire Department that some the fire system is fully operational in the event a fire case occurs during the absence of the mains supply which include also some lighting for evacuation purposes.
The Fire Department requirements on the standby electric generators
The Fire Department usually requires that the standby generators be up and supplying load within a few seconds (within 15 seconds the last time I checked, if I remember it correctly. This number may vary slightly from country to country.) from the moment of mains failure. However in practice, some generators in some installations are up to this performance. It can take longer.
Even with 15 second blackout, some works in the hospital may be disrupted long enough to cause danger to patients. The prime examples are the procedures in the operation theatres (OT) and the patients who are continuously dependent on some live-saving machines.
The UPS batteries
Therefore the UPS system is installed to fill this 15-second gap. The batteries in the UPS system will be supplying power only for this 15-second period plus a few seconds more added inside the UPS system settings to make sure the electrical supply (the mains supply or the standby generator’s supply) is stable before the UPS storage batteries are switched out of the supply circuit (and back into the charging circuit).
That was the case when the standby generator is up and running within 15 seconds. What if it takes longer (never mind the fire regulations regarding this)? What if the generator actually fails to start? In can happen, and it does happen, as the case when the starting batteries fail to supply sufficient voltage after a few years because of negligence by the maintenance team.
I purposely drag this point longer just to emphasize it, just to stress on the critical function served by the UPS in the backup electric supply system of a hospital.
More points on the distribution system (which I will elaborate further soon)
1. A substation’s low voltage section consists of the Main Switchboard (MSB), the Essential Main Switchboard (EMSB) and a bus coupler. The EMSB board supplies the required essential lighting, power and critical equipment in the Hospital Complex. Part of it also will serve the mechanical load such as air condition, compressed air, vacuum system, and boiler and fire protection system.
2. Local UPS will be provided to support the emergency power requirements of critical loads.
3. The normal, essential and emergency supplies will have separate main switchboard, sub-switchboard and distribution board to supply the respective lighting, power and mechanical services.
4. All switchboards and distribution boards will be provided with suitable types of protection. The sheet metal materials of the board enclosures will be of electro-galvanized type.
5. The design will provide at least 20% spare capacities in all switchboard and distribution boards for future needs, while the main switchboards will be provided with a spare capacity of 30 percent. The main switchboard of the hospital complex will be installed with an automatic power factor board and capacitor bank to keep power factor of the installation at not less than 0.85 lagging in any load condition.
6. A power monitoring system will be installed at the incomers. They will monitor the incomers for all the important electrical parameters including harmonic and also load shedding of non-essential loads. It will also be able to communicate with remote stations by any microprocessor.
7. One bulk electricity meter is provided for the hospital complex including the staff accommodation buildings. Separate meters will be provided for the retail spaces, the cafeteria, canteen, kitchen area, staff quarters and any other spaces for hospital functions that are planned for privatization by the hospital management.
However, as the detailed design develops, a separate bulk meter taking a supply at low voltage from the authority may be provided for the staff quarters, nurses’ hostels and housemen mess.
The reason being the limit set by the authority that any new site with load demand bigger than 5 MVA are required to surrender an empty 100 feet by 100 feet substation space for a future 33/11 kV substation.
At present, the estimated maximum demand for the whole complex including the accommodation area is 5.5 MVA, which has exceeded the % MVA limit.
As the detailed design is developed deeper, in tandem with the gradually more information available on the end-user requirements from the Client-Contractor interaction sessions, the expected maximum demand may be trimmed to below 5 MVA.
If it cannot be trimmed down to below 5 MVA, the application of supply that will be submitted to the electric supply authority will request two bulk meters: one HV bulk meter for 4.8 MVA that will supply both the Hospital Substation and the Mechanical Plant Substation.
The other will be an LV bulk meter for 700 kVA at the Accommodation area Substation which will provide supply to all the accommodation buildings.
Many times the authority approved this arrangement. However, there have also been cases where these types of arrangement were rejected.
B. Cabling and wiring
1. Normal, essential and emergency circuits should be installed in separate trunking and conduits. They need all be properly labeled.
2. All cabling and wiring should be in G.I. conduit. All trunking / tray / ladders shall be of unpainted electro-galvanized sheet metal and marked with proper a color coding system.
C. Electrical socket outlets
Minimum two 13A switched socket outlets should be provided for each bed in the normal wards whereby one of them is connected to essential supply.
Isolators should be provided to suffice the requirement of all equipment.
D. Fans
1. In buildings or rooms where air-conditioning is not provided such as at certain selected wards and at the residential buildings, fans should be installed as required.
2. The sweep fans provided should be complete with speed controls, located at the entry door.
E. Lighting installation
1. A hospital is a very complex, task-intensive institution. The selection of lighting services and control gears should be on the basis of functional aspects, energy efficient, good color rendition and low maintenance.
2. The lighting for various areas should be designed in the compliance with IES, DHSS and current Work Ministry’s code of practice to achieve the average illumination levels as described in attached schedule (will be uploaded later).
3. Labor room, Procedure room, Autopsy room and Treatment room should have the ceiling mounted examination light 0f 30000 lux.
Electrical HV switchgear installation pictures for hospitals
Below you may find some pictures (Well, only one for now.) on electrical installation in hospitals. I may upload more of them in future when I come back to finish on the short sections remaining in this post. So stay tuned.
P/S: You can also see quite a number of electrical installation pictures that I have uploaded at this post: Temporary electrical installations
Picture 1 - Hospital HV switchgear installation in progress
Picture 2 - HV switchgear installation - Rear view
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