Tuesday, April 26, 2011

Neutral Link Pictures

I just wish to show a few pictures of electrical neutral links here.
Picture 1 – Neutral links on electric meter panels at a commercial shops building

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.

Now, the pictures.

(Note: I took the above photograph at a commercial shop-lot building a few months ago. Never mind the blue pieces of paper below the electric meters. They were survey stickers left by the national statistics department. The department was doing a survey of the local population when I took the picture.)

There are two kilowatt-hour meters on the picture.

So there are two units of neutral links there.

Picture 2 – A neutral link unit

This is a close-up view of one of the unit on the panel. I did not look at the rating of the cut-out fuse there.

However, it could not have been less that 100A. A standard cut-out fuse rating for single phase supply to a normal house is 60A. A commercial lot like this would need more usually.

I have not been doing design or supervision on commercial lots of this types for some time. I am getting rusty.

Picture 3 – Neutral link, cut-out fuse and kWh meter connections

Here is a good picture to use if you wish to test how good you are in electrical connections.

The electric meter panel on the left has not yet been installed by the electricity supply company.

This is a newly completed building and a number of the shop units have not yet been occupied.

The electric supply company would only install the meter if the owner or the tenant of the unit submits the supply application form and pay the necessary connection fees and deposit.

Apparently the owner or the new tenant has not yet done so.

The good thing is you can understand more clearly how the wiring on the meter panel including the connections to the neutral link are run.

The cartridge of the cut-out fuse also has not yet been installed. So you can see the inside of the fuse base more clearly. The picture below shows them at a closer view.

Picture 4 – Base of cut-out fuse installed but not yet wired

Now see the picture below and test yourself if you can mentally complete the wiring of the meter panel on the left. You can use the completed panel on the right as a guide.

Picture 5 – Meter panel wiring test

If you think the neutral link on a house electric meter panel is kid’s stuff, then look at the photograph below.

Picture 6 – Internal wiring of a three-phase electrical distribution board

This is a three phase electrical panel for the lighting and power of an office floor.

If you look closely, you will notice that the incoming power cables are not yet terminated to the panel’s incoming circuit breaker.

The incoming cables are still dangling down from the top of the panel going wown on the right side.

Observe also the rows of miniature circuit breakers (MCB) near the top of the panel. The is no wiring yet on one side (the lower side) of the MCB terminals.

This is because this distribution boards is factory manufactured. All internal wiring are done at the factory.

The wiring that goes out of the panel would be don’t at the construction site. Here the supply cable to the panel has been installed. Only the termination to the main circuit breaker has not been carried out.

Back to neutral links. Look at the picture below:

Picture 7 – Neutral link of main incoming circuit breaker

Here is the neutral link of the main incoming circuit breaker.

This neutral link is installed inside a protected compartment. That is why it look so different from the neutral on the electric meter panel in the earlier pictures above.

The meter panels were exposed. So there has to be some enclosure to protect the component inside and also the connections of the cables.

Inside a protected compartment like this distribution board, many of electrical components are simply bare.

The neutral link here is just one example.

Picture 8 – A closer view of the neutral link

Notice that only one side of the neutral link hase been connectied by a cable. This the internal wiring that has been done at the factory.

The terminal without cable connection yet is the one to be connected to the neutral cable of the incoming supply.

Observe also that the cable is terminated to the neutral link terminal using an “O” ring type of cable lug.

This is very important in the connection of power electric cable and wiring. A ring type of cable lug has a hole at the center. The bolt would go through this center and hold the cable firm with two nuts above and below the cable lug.

(Note: If you are not sure what a cable lug is, it is a conductor extension that is installed at the end of a cable conductor so that the connection to a terminal can be made much easier, faster and much much more reliable.)

Even terminal connections of an 11kV high voltage cable are done using a similar ring type of cable lug.

Picture 9 – 11kV cable terminations

Picture 10 – A closer view of the ring type of cable lug for high voltage cable

I added this picture on 11kV cable termination just to emphasize this very important point in electrical installations: the soundness and reliability of power cable connections.

Well, I guess that is all I wanted to say on neutral links today. I just wanted to show the pictures so beginners have a “confirmed” view of what it is.

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Friday, April 22, 2011

Lift motor room layout drawing

I have attached a layout drawing for a lift motor room here. It is for the same building as the nurses’ hostel building in the previous post that I sent on electrical riser rooms.
Part Drawing 1 – The lift motor room layout drawing

A building’s lift motor room is mechanical plant.

However, it is also a very important part of an electrical design engineer’s scope of work during the design and planning of a building project.

In many construction projects, this is one of the areas of the building space where the architects, structural engineers, mechanical engineers and electrical engineers battle each other for simplicity and easy design of their own scope the design work.

In a complicated building design for a building owned by private clients, the client herself might enter that battle zone just to make sure that the final design would be one with lowest cost of construction and takes up a minimum space possible.

Not that there is much space that can be rented out at a lift motor room level, but the attitudes seemed to encompass almost everything.

Part Drawing 2 – Riser rooms and lift shaft layout drawing

I just attach this drawing again here for the benefit of beginners. It was already included in the earlier post on riser rooms.

Compare the two diagrams together and observe the riser rooms for electrical (ELEC), master antenna TV system (MATV) and telephone (TEL) in Diagram 2.

This is an eight-storey building with the lift motor room at the ninth floor (the roof level).

So all the electrical riser shafts stop at seventh floor including the cold water shaft.

I am not going to say much on the lift motor room today. I just wanted to share with you this drawing.

In any case, beginners only need to study the layout and try to see the logic of why something is located where it is. There are enough labels on the drawing to indicate what that something is.

If the description is not enough, try to make a guess.

For example, “DB ELMR”. DB stands for distribution board. That is a standard notation for electrical distribution board. The symbol there is also quite standard.

ELMR? You guessed it. LMR stands for Lift Motor Room. While the “E” has been added to indicate that this distribution board has been supplied (electrical supply) from the Essential supply of the building.

Essential supply is the power that has been backed by the standby electricity generator of the building.

I will upload the single line drawing for the lift switchboard (not the lift control panel) and the DB ELMR soon. With that you will be able to see the overall picture of the distribution system here.

I could have uploaded the drawing in this post, but that could confuse the search engines about the main keywords for this post.

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Electrical riser rooms

This post talks about electrical riser rooms, or electrical service ducts, as they are sometimes called. These rooms are usually not so obvious. They don’t look prominent, not like the standby generator rooms or the high voltage rooms.

Picture 1 – A partial view of an electrical riser room at a high rise office building

Picture 2 – Another view inside the same riser room (on the left of the bus duct risers)

They are still needed, however, for a proper and efficient operation of an electrical installation in buildings especially those of the multi storey and high rise types.

They are used to house the vertical submain cables that carry electricity supplies to the upper floors of the buildings and to the plants and machines at the roof top such as the chiller plants, cooling towers or the lift motor rooms.

The vertical rising mains that supply the lateral distributions on individual floors are also installed in these vertical ducts.

Often these concrete vertical ducts are as large as a small room. That is why it is often called electrical riser rooms.

The electrical riser rooms do not have to be stacked vertically like the toilet risers or wet stacks.

However, it is better to do so as it would minimize turns and sharp bends that can damage the cables.

Riser rooms stacked straight up from the lowest floor to the highest building floor would also minimize the length of the electrical cables required.

Minimum cable length not only reduces the cost directly. Longer route of an electrical cable run may cause too much voltage drop along its length that may require it to be changed to one or two size larger.

Larger cables cost more money.

Diagram 3 – A ground floor layout of building services

Diagram 4 – A zoomed in view of the electrical riser rooms’ layout

The above two diagrams shows an example of electrical risers in an actual design. Diagram 4 is actually a zoomed in view of the electrical riser area to give you a clearer view.

This layout is for a nurses' hostel building at a large hospital. There were a whole range of residential buildings there so I picked this one as an example.

I will just explain a little bit here to help beginners get started.

ELEC – electrical riser room.

MATV - the riser room for the MATV (master antenna television) system. If the building has a CCTV (closed circuit television) system, the riser cables will run inside this riser shaft to connect to upper floors of the building.

In many building design, a single riser shaft is used to run all the ELV (extra low voltage) services to the upper floors.

(Note: When all the riser rooms at each floor are stacked up vertically straight up, then it forms a shaft. So it is called a riser shaft.

Put in another way, a long time ago when the ancient builders found out how to build a building with multiple floors one on top of the other, the riser started as shaft or a vertical wooden duct.

In order to make it safe for working inside it at each floor, they extended the floor into part of the riser. Then it became like a room. So it was called a riser room.)

TEL – for telephone cables and equipment.

DR – dry riser. A building exceeding a certain height is required to install vertical pipes with inlets at the ground level. These pipes will be used to pump water from fire engines to the upper floors so the firefighters can fight fire.

If the building height is even higher, dry pipe riser would not be accepted by the fire department. A wet riser system would then be required. This is the same piping as the dry riser but with water tanks to store water and sufficient number and horsepower of pumps to always keep the water under sufficient pressure in case there is a fire in the building.

WATER – Water is not available here. Just pipes that carries domestic water. Designers just label it WATER as a short form for COLD WATER.

ON CALL – You would only have this at residential buildings for hospital employees. They have a communication system that can call the employees on standby when they have to report for duty immediately.

The red rectangular symbol inside the electrical riser is the electrical panel. You will find one or more electrical panels at the upper floors also.

(Note: The ELEC, MATV and TEL riser rooms are all part of the electrical risers. All these systems are part of the electrical services in a building system.

Many building are equipped with building automation systems or sometimes called building control systems. Many engineering firms classify this system as a mechanical system and therefore it is designed by the mechanical engineers of the firm.

Some consultant companies, however, consider that it part of electrical systems. So we the electrical engineers need to take care of all the designs.

Likewise for vertical transportation systems such as lifts and inter-floor escalators. However, a much smaller number of engineering consultants put this under the scope of electrical engineers. A few still practice that and I happen to be working for one of those firms many years ago.)

Individual floor electrical rooms

Each individual floors of a significant size usually needs at least one dedicated electrical room to house the electrical distribution equipment for that floor.

Sometimes the vertical service ducts may be able to fulfill this function in which case a separate electrical room may not be necessary.

The architect may then need to make these service ducts bigger to give them enough space for proper operation and maintenance.

The electrical rooms at each floor house the electrical panels that serve the final circuit wiring.

Therefore, they should be as close as possible to the load center of the area that it serves.

I will upload some detail layouts of the electrical riser rooms in future posts for readers who need them.

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Thursday, April 21, 2011

Copper earth rod pictures

Here you can see a few pictures of electrical earth rods inside inspection chambers. These are all copper-jacketed steel rods with 16mm diameter.

Picture 1 – An earthing rod installed inside a precast concrete inspection chamber

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.

Picture 2 – A close up view to show the exothermic welding of the earth rod to the earthing PVC copper cable

Here I zoomed in a little bit into the earlier picture to show the type of bonding between the copper-jacketed earth rod and the copper earthing cable.

I personally always prefer that this connection is done using a suitable type of compression clamp.

However, this particular client has made it a rule that in all their building projects, the connections between earthing conductors and the earth rods must be done using a permanent bonding method such as the exothermic welding here.

This particular client was a very large organization who has to maintain many installations throughout the country. So I assumed that they were having some concern about the alertness of some of their maintenance teams on the ground to this aspect of safety.

If the concern was real, I would definitely agree with a permanent bonding like this. In this way there was minimal risk of quality at the connection being degraded over time.

Of course if there is a need to make an additional connection here in future for some reasons, then the task will be a bit difficult. But it can still be done although not in a very proper way.

Picture 3 – Connection of earth rod to earth cable using compression clamp

Here is an example of the connection using brass compression clamp. I had the contractor used this method first to try to persuade the client accept it. But they didn’t.

Picture 4 – A closer view of the compression clamp connection

Well, the workmanship of this connection could be much better. But since permanent bonding was insisted, the connection was changed to the exothermic type.

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Tuesday, April 19, 2011

Simple house electrical layout

Are you looking for a simple house electrical layout drawing? This is your lucky day. I just uploaded one and you can see it below.

Drawing 1 – An electrical layout drawing for a two-bedroom small house

I am not going to explain much on this drawing because every time I try to explain something, I cannot stop until a short post is no longer a short post.

However, I still need to say a few things so that beginners have some direction of what to do with this electrical layout.

First of all, every time we see a new layout, we need to make sure how the drawing designer want us to interpret the drawing.

Simple said, we should ask the designer where the Schedule of Legends and Symbols for the drawing is.

In this particular case, I did the drawing. So I am the designer.

So you need to ask me where the symbol list is.

My answer is this post, House electrical symbols, which I have already posted earlier.

However, I feel the need to tell you that this electrical layout is not designed by me.

I think it has originally been designed by some British engineer tens of years ago when they were occupying this country.

The design must have been good enough to have survived until very recently.
 Very few changes have been made other than the Miniature Circuit Breakers to take place of fuses to protect the final circuits. This you can see in the single line diagram that I have just uploaded at this post, Simple house electrical schematic.

Tens of thousands of government quarters has been installed with electrical wiring using these electrical drawing (the layout, the single-line schematic diagram and the list of symbols).

So the design is a proven one. I did the draughting myself, however, because I did not want any possibility of copyright issues. In any case, these are just very small drawings.
Click here to go back to the original article, Home electrical wiring, symbols and checking.

See you in the next post.

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Simple house electrical schematic

Many visitors came to this blog looking for a schematic diagram for a simple house wiring. The original post, House electrical wiring, symbols and checking, is too long. Many readers clicked away. My guess is that they cannot find the schematic drawing. So I decided to separate it into a small article, here.

Diagram 1 – Schematic diagram for a simple 2-bedroom house (Click to see full size)

In the original post, I gave a lengthy description of how to read this schematic so beginners understand how to read the electrical single line drawing.

I will not do that here. Many people don’t like long posts so I will try to make it really short.

However, there will be a number of small posts on house electrical installations and wiring. Therefore, all the materials will still be covered.

Using separate articles, I will try to explain them from different angles so all readers from different backgrounds will be able to understand them. That will be the way I will present these things to you.

The electrical schematic in the above diagram is a “single-line diagram”, or a “one-line diagram”. That is how to say it more precisely.

The word “schematic” gives an impression of a “wiring diagram”. If you have a wiring diagram, you can do a wiring work if you follow what is shown in the diagram precisely.

Unless you are an electrician, or you already have electrician’s skills, you cannot do a house wiring using the above electrical schematic drawing.

If you are a beginner and you try to do so without learning enough on the shock protection side of the wiring circuit, your wiring work may still seem to work perfectly.

However, the wiring work you have just completed may present electric shock hazards that you may not understand until too late.

I am not trying to turn any reader “off” by saying these things. Skills in electrical wiring is a kind of “survival skill” so everybody should know a little bit about it.

But the voltage of house electricity is a “lethal voltage”. It is a high-power voltage. If not handled properly, this voltage can kill people. It happens all the time.

So while you are in a high spirit to learn the house wiring, remember that you also need to learn the how to prevent the electric voltage inside your wiring from causing electric shock to people including yourself.

With that said, let us now go to the short description of the house single line diagram.

A. Incoming electricity supply and the electric meter

Let’s just start at the bottom of the single line drawing. Some people draw the single line from left to right. This one starts from the bottom. Both approaches are common for an electrical drawing of this type.

Image 2 – The electric meter panel symbol

The rectangular box here is represents the electric meter panel. All components inside the rectangle are actually on the meter panel in actual installation. This you can see in the picture below.

Photo 3 – A house meter panel

Remember that a single-line drawing is not really a wiring diagram. When one line is shown on the drawing, it does not necessarily mean one wire or one cable.

The wiring only shows the flow of electricity and the electrical connections in general between the electrical parts or components. You need to see closer to see if there are more details indicated on the drawing.

Image 4 – The supply cable symbol

Here I just extract out the symbol of the electric cable on the electric meter panel.

As you can see the drawing gives a label to describe some details of the cable from the KWH METER to the 60A SPN SWITCH FUSE.

It says 2-25 SQmm PVC/PVC IN CONCEALED CONDUIT. That means we have two lengths of cables with the size of 25 millimeter square size.

The “SQmm” is a short hand for “millimeter square “. It is the net cross-sectional area of the cable conductor, the part of the cable that carries the electric current.

Photo 5 – The 25 millimeter square electrical cable with PVC/PVC insulation

The word PVC/PVC in the label means the type of cable insulation. All electrical cables must be insulated. Otherwise the conductor part (the copper part of the cable, or the aluminum part if it is an aluminum cable) can be exposed to touch and cause danger of electric shocks.

Without insulation, a short circuit between electrical parts or components can easily occur which will damage the components and also cause fire to the house. That is one of the ways how house electrical fires happen.

PVC is a popular type of materials used to insulate electrical things including cables, socket outlets, etc. It is actually a similar material (but not exactly the same) to the house PVC pipes that are used in house water piping.

B. The consumer disconnection fuse and main circuit breaker

From the meter panel, the 25 mm square cables are run in a concealed conduit into the “Consumer Panel”. People in different countries call this panel by different names: electrical DB, house DB or simply DB, electrical panel, consumer unit, supply DB, etc etc.

Basically it is a box in a house that controls the distribution of electricity to the whole house.

Photo 6 – A house electrical panel

Remember that the electricity meter panel belongs to the supply authority. Well, not really the whole panel but that is generally the idea.

The consumer panel, on the other hand, belongs to the consumer. You can literally do whatever you wish inside the electrical panel. That is an advantage but it is also a source of so many problems and electrical accidents and fires.

The 25 sq.mm cables are connected to the consumer disconnection fuse or the main circuit breaker. Both methods of disconnections are commonly practiced but for this house electrical design, a disconnection fuse is used.

Image 7 – The switch fuse symbol

The label “60A SPN SWITCH FUSE” is used to describe the component used in this electrical design.

The main purpose of this part is to stop the flow of electric current from the meter panel to the house wiring when too much current flow through the fuse. A number of problems can cause too much current flow that will “blow” the 60A fuse.

I am not going to go into details here. That will be in separate posts.

Photo 8 – The house switch-fuse - refer Photo 10 (The house ELCB) below.

C. The electric shock protection section or “ELCB”

From the 60A fuse, the electric power flows to the shock protection section of the electrical panel. We call this component “ELCB” or earth leakage circuit breaker.

The label “100 mA” below “63A DP” says that the ELCB will trip when it detects a leakage cureent of more than 100 milliamperes. It is the level of sensitivity of the ELCB unit. There are ELCB unit sold on the market with other sensitivities such as 30mA or 300 mA.

The name (i.e. ELCB) of the shock protection component is really just a conventional name from the old days of electrical engineering. It is still widely used today for the electrical drawings of house electricity.

Image 9 – The earth leakage circuit breaker symbol

Nowadays the technology has changed and the right name of the shock protection component used in home electrical panels is “residual current circuit breaker”. The short form is RCCB.

However, other names are also used to say the same thing: residual current device (RCD), residual current circuit breaker with overcurrent (RCBO), etc.

Whatever name is used at your locality, this is the second component in your house electrical panel.

The picture below shows an example of house ELCB. The ELCB is the unit on the right with the word CLIPSAL on it. The unit on the right, with the word NEM is the switchfuse.

Photo 10 – A house ELCB

After the electric voltage passes the earth leakage circuit breaker, then it is ready to be distributed throughout the house.

The next section provides a brief explanation for that.

Before that, however, I wish to bring your attention to one important point of the house single line diagram.

Image 11 – Split-busbar electrical panel

This is important because many common electric users get confused and take actions that expose themselves to a very high possibility of electric shocks.

The above part-drawing shows what is sometimes called “split-busbar”.

I guess that name came about because the long busbar in the electric panel has been split. If you do not know yet what a “busbar” is, it is just a piece of long metal inside an electrical equipment that is used to more conveniently distribute current to many branch circuits.

A cable can also be used to do this, but it is often much easier, economical and more reliable to just use a long piece of metal for the purpose. It is called a “busbar” and is one of most common electrical terms in the electricians’ world.

In a house electrical panel, often a busbar is used. Often, but not all the time. Many lower-cost electrical panels just use cables.

In the single line drawing of a house electrical panel, however, the busbar symbol is almost always used regardless of whether the actual part used is a busbar or cables.

That means after the ELCB symbol (or RCD), you will always see the busbar symbol in the diagram.

On the image, I labeled the lines that represent the busbars.

The labels “5A SPN MCB 6kA” and “20A SPN MCB 6kA” are the symbols for the circuit breakers that protect the branch circuit. These branch circuits are the wiring that go to the house lighting fixtures, light switches, wall sockets, etc.

Why has the busbar been split?

The busbar has been split (one length of metal busbar “splitted” into two pieces) because we need to install two units of electric shock protectors each with a different level of sensitivity.

One is 100 mA and the other 30mA.

Observe that the branch circuits that are connected to the busbar with 100mA ELCB are the lighting circuits.

While those connected to the busbar with 30mA protection are the switched socket outlets.

I have sent a long post on the details of ELCB at this post, ELCB – Home electric shock protection. So I am not going to go through the details again here.

The important point that beginners need to remember is that 30mA is the absolute maximum current that the human body can take before serious injuries including death.

Therefore all 13A house socket outlets must be connected to a busbar protected by a 30mA ELCB.

Can we connect the house lighting to the 30mA busbar?

Yes, we can. However, over time a lighting fixture can leak a significant number of miliamperes of current.

If the house has a large numbers of lighting fixtures then the 30mA limit that the ELCB can handle can easily be exceeded. The result is frequent tripping of the ELCB.

When this sort of happening occurs, many users just disable the ELCB in any way they can, or bypass the ELCB altogether. Then they no longer have any protection from the possibility of the electric shocks.

Some users may be smarter, they go to the hardware shop and purchase a 100mA ELCB. They install this in the house electrical panel and keep the origibal 30mA ELCB just for spare.

Now with the socket outlets protected by a 100mA ELCB, the protection provided by this arrangement against electric shocks is very limited if there really any at all.

So this is the reason why the busbar in the house single line diagram has been split and two ELCBs of different sensitivities have been used.

D. The distribution busbars and the branch circuits

I think I have said enough about busbars for a short article. If there is a need I will use a separate post in the future just to give more detail and examples.

Now let’s just go to the distribution of the electric power as shown in the single-line diagram.

Image 12 – The distribution section of the electric panel

As said before, the busbar is used so that the connections for distribution of the electricity to the branch circuits can be done more conveniently.

This is one of the most important purposes of a house electrical diagram. With the diagram, we can see clearly how the current is distributed.

Symbol 13 – Miniature circuit breakers (MCB)

The above is the symbol of the miniature circuit breakers or simply called MCB in daily use.

Observe that for each outgoing circuit one miniature circuit breaker is installed. The MCB’s main purpose is to protect the cable that is supplying current for the electrical appliances or other electrical loads connected to that circuit.

Photo 14 – 20A Miniature Circuit Breakers (MCB)

Take note also the small circles with the numbers 1 to 6 at the end of each line of the branch circuits.

Symbol 15 - The circuit number labels

Each circle with the number is the circuit number for that branch circuit. It is the circuit label. Since there are a number of branch circuits in a house wiring, each circuit need to be uniquely labeled for safety and also for convenience during installation and during maintenance.

There are many ways to label a circuit number. This particular method is most suitable for wiring of small houses.

You can see how convenient these circuit labels are when reading the electrical layout drawing of the house.

You can see the layout drawing for this design is post, Simple house electrical layout (Coming soon..).

If you cannot wait, you can see it now in the original post, Home electrical wiring, symbols and checking.

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Monday, April 18, 2011

House electrical symbols

If you are looking for a simple list of house electrical symbols, below is one.

If you are surprised at how short the list it, then please know that this list of electrical symbols has been used in this country for thirty or maybe forty years.

As I said, I am breaking up the original article, Home electrical wiring, symbols and checking, into a number of small posts for the benefit of beginners so they can easily find what they are looking for.

Lighting symbol 1: 4 ft, 1 x 36 watt fluorescent light fitting, wall mounted type

Lighting symbol 2: 2 ft, 1 x 18 watt fluorescent fitting, ceiling mounted type

Lighting symbol 3: Globe-type light fitting complete with 1 x 60 watt incandescent bulb, wall-mounted type

Lighting symbol 4: Globe-type light fitting complete with 1 x 60 watt incandescent bulb, ceiling-mounted type

Fan symbol: 60-inch ceiling fan

Socket symbol: 13A 3-pin switched socket outlet, wall mounted

Switch symbol:  One-way 5A light switch

Fan switch symbol: Ceiling fan speed regulator, complete with ON/OFF switch

DB symbol: All-insulated 6-way consumer unit, complete with MCB and ELCB, wall-mounted type

Electricity meter symbol: Authority’s meter panel complete with cut-out fuse and neutral link, wall mounted type

There you have it. The symbols for a simple house electrical installation.

I have broken up the symbols from the original drawing for the benefit of the internet search engines, so they can find this post easily. That also means internet users can find them easily.

You can see the original symbol list below:

Diagram 11: House electrical symbols

You may notice that the original list contains a QUANTITY column on the right. (Click in the image to see the full size.)

This is the actual quantity of the materials in the original electrical layout, which you can see at this post, Simple house electrical schematic (Coming soon... ).

That is all I wish to say in this post. I will see you again in the next small post.

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Friday, April 15, 2011

13A sockets inside underfloor box

These are just pictures of two units of under floor service boxes with 13A switched socket outlets installed.

Photo 1 – 13A switched socket outlets inside underfloor junction boxes

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.

Drawing 2 – Layout drawing of an underfloor trunking system for a high-rise office building

This is an example of an under trunking system layout drawing for an office building.

It was part of a whole set of tender drawings that was being used by the electrical sub-contractors to price their tenders during the bidding process of trade sub-contracts. The main contract was a negotiated-price design-and-build contract. All specialist trades were tendered out in an open tender process.

Many readers can probable make out the underfloor trunking system by just looking at the layout drawing. If you are not sure, below I extracted out some of the relevant symbols.

Image 3 – Junction box symbol

Image 4 – Service box symbol (Type 1)

Image 5 – Service box symbol (Type 2)

Image 6 –Symbol for cast-in-situ three-way underfloor uPVC trunking

Image 7 – Symbol for above ceiling 50 mm x 50 mm G.I. trunking

Image 8 – Two symbols of 13A switched socket outlets

As you can see, the underfloor service boxes are always located somewhere under a worktable (many architects prefer to call them “workstations”).

On the other hand, the junction boxes are always located at the junctions of the underfloor trunking system. It functions just like the conduit draw boxes at a wiring conduit system.

With the junction boxes at a certain maximum intervals along the underfloor ducting and at every corners and junctions (or intersections), the wiring cables can be easily drawn in during the wiring works.

This also helps during maintenance works.

In this design the underfloor ducting is a three-way uPVC type. That means there were three uPVC ducts along from one junction box or service box to another.

The three ducts were meant one each for 240V socket outlet wiring, telephone wiring and computer network wiring.

I am not going to go into many details about the whole underfloor ducting in this post. I just want to explain it in overall perspective to give a background to the issue of the 13A socket outlets as in Photo 1 above.

The 13A switched socket outlets

If you look closely at the above photograph, the power socket in the service box on the right is similar to the type normally used on walls.

While sockets installed inside the left service box is a fully flushed type.

The ones on the right are also called a flushed type, but in reality they are not 100 percent flushed into the surface they are mounted on.

The result of both these two types of socket outlets can be seen in Photo 8 below.

Photo 9 – The underfloor service boxes with the lid covers in closed positions

You can clearly see here that the lid cover of the right service box did not get  into a fully closed position.

Both lids were already pushed all the way down.

The service box on the right would be damaged together with the sockets in it after duration of use.

I believe that readers who have worked with junction boxes before might be asking: What the big deal about it? Either the choice is the left or the right one, either one would be able to work because the service box itself is adjustable vertically.

And both types of socket outlets are not that much different in terms of costs.

That is very true.

The problem here was contract management, not the technical or the implementation part of it.

During the proposal stage three brands of the socket outlets were submitted for approval to the client project managers.

This was a government contract and by the established procedures, in a design-and-build direct-negotiation contract, a main contractor was required to submit three brands of each equipment and material for approval by the government.

Whatever three brands were approved, all three were to included in the signed contract after the price was agreed on negotiation.

It was a good strategy. With three different manufacturers competing for each equipment, the main contractor would logically get a reasonable price during the tendering of trade sub-contracts.

At times, however, the government project managers at the last minutes decided to insist that only one brand for each equipment would be included in the signed contract. During those last minutes, without much time for the engineers to do enough study, one brand was chosen to be bound into the contract.

The main contractor therefore went to the negotiation table with this requirement and committed to the agreed price.

Later, things happened.

In this case, as it happened, the brand that was chosen did not have the fully flushed type of socket outlets.

To make things worse, nobody (including me who looked after the installation works at site) noticed until all the underfloor trunking system were cast into the concrete floor.

If it was realized earlier, the service box height could have been adjusted vertically during prior to the floor screeding works.

The thickness of the reinforced concrete floors could have been adjusted also.

However, once all the concrete floor works have been completed with the service boxes cast in, then there was no more choice.

The make of the socket outlets have to be changed.

Being a government contract, approving the change of brands after the main contract has been signed can have serious consequences on the government officials involved.

In a private project, this is not an issue at all.

A public project has a much higher political factors involved.

On many occasions, change of brands of the equipments and materials was totally forbidden.

Then that small problem above would become a really huge problem.

Note: This anchor post, Free electric installation pictures , may contain a summary of the materials you are looking for. It can be faster than clicking through each post title at the Blog Archive. I started it long ago but never actually got around to finish it.

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