Thursday, December 31, 2009

Electrical DB pictures

I have uploaded below a few pictures of electrical DB being installed at a high-rise office-building project. I only have enough time for these few pictures today, but I will be sending a more detailed post on the DB installation soon. Plus a few more of the DB pictures maybe.

In the meantime, if you have 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 of our daily transport costs. Check it out. It’s a good reading.

Picture 1 – Mounting position and location

These electrical boards are permanent boards, not a temporary electrical installation. I have been sending so many pictures of temporary electrical installations that I feel the need to make that clear. Otherwise, some readers may get confused because in these pictures you can see that the boards and the cable trunking are solidly mounted on the concrete wall.

Actually there are three DB’s in this picture. The two big ones on the left (your left side) are the electrical distribution boards (DB) and the one at the far right is the telephone distribution panel (some people call it “DP panel”).

These DB’s are located along one of the corridors on the office floor. Therefore, they will need to be hidden from view and protected from unauthorized access. Therefore, a cabinet will be built around these boards, and a lockable door will be provided.

The installation work is in progress and the building is still under construction. However, if you see closely to the doors of the distribution boards, you may notice that the DB doors are not provided with lockable door handles. They seem to be provided only with door screws.

With this type of doors, then they are not protected from access to the live parts of the boards. So, if there is no provision to build such electrical cabinet or rooms as I have mentioned and secure it with lockable keys, then the construction supervisor in charge of the electrical installation must insist for it.

There is no problem in installing the distribution boards exposed like that. However, they must be protected from unauthorized access. In this case, you have three choices:

Provide lockable doors and raise the mounting height of the DB’s above reach by hands.
Raise the mounting heights to unreachable heights without providing the lockable keys to the doors. This a little bit of a compromise already, but some may say that is already okay. In many scenarios this sort of issues are quite subjective.
Build a cabinet around the boards, enclosing all three electrical and telephone boards. A lockable door should be installed.
Build wall around them so it will become an electrical rooms, plus a lockable door.

Picture 2 – Dropper trunking from above ceiling

This second picture shows the metal trunking coming down from above the ceiling and into the distribution boards.

Some of you may be wondering why these trunking are like that… with the big trunking branching into the smaller ones above the ceiling. The reason is to make the space bigger for the wiring cables to crisscross each other while coming out of the MCB’s (miniature circuit breakers) inside the DB’s and into its intended trunking route (either one or the three branch trunking above the ceiling.

Actually, the three branches of trunking above the ceiling is for the following:

One for lighting wiring final circuits. All wiring cables supplying all lights and maybe ceiling fans and toilet exhaust fans. This is an air-conditioned office building, and ceiling fans are not used at all. However, wiring for the air-conditioning equipment is not allowed to run in trunking for lighting wires. Emergency light and the lighted exit signs also have their wiring installed inside this trunking, but the one from the ESSENTIAL SUPPLY board.

I should have mentioned this earlier. We have two electrical DB’s there because one is supplied from the standby electrical generator. This is the smaller DB. The bigger DB is supplied from the authority’s mains supply. The one supplied form the standby electrical generator is usually called “essential DB” or “essential distribution board”, while the one supplied from the mains is normally called “normal DB” or normal distribution boards.

The Essential DB is usually smaller because the number of electrical loads it need to supply is smaller. In ordinary office buildings, the number of light fittings that need to be turned on during a power supply failure is usually only one out of three lights or about thirty percent of the general lighting. So the Essential DB will have only half the number of final circuit wiring as the Normal DB. That is why they are generally half the size, which is what you can see in this picture.

The second branch trunking is for the small power final circuit wiring, the wiring supplying all the switched socket outlets and other small power points like window air conditioners, etc. Cables supplying power to other mechanical equipment such as water pumps, etc are not allowed to share this trunking. The need to be installed in a separate trunking, which is the third branch trunking.
This carries the cables and wiring for the mechanical equipment like the building’s water pumps, etc.

So the above describes what those three branches of the metal trunking are for. The same applies for both DB.

Picture 3 – Bottom cable entry

This picture shows the bottom entry for cables. Both DB’s has bottom cable entry. Some of the readers may be wondering why cables need to enter the DB cabinet from both to and bottom. The reason being this is an office building with an underfloor trunking system.

The electrical socket outlets, the telephone socket and the computer data sockets for all office tables are provided from outlet boxes of this underfloor trunking system. So there are three separate high impact PVC trunking running inside the concrete floor throughout all office areas of this multi-storey office building. At each worktable, an outlet service of approximately 12 inch x 12-inch box is provided and all the power, telephone and data sockets are provided there.

You can see that the orange electrical trunking under the DB’s going downward to the floor. The green telephone DB also runs downward to the same location. This is where they are connected to the 3-way underfloor trunking system. The piece near the floor is called the “vertical access box” of the trunking system.

That is all on the bottom trunking for now. In future, I will talk more on the underfloor trunking system and maybe show you some real construction photos.

The top entry trunking are for all other cables and wiring. The wiring to the window air-conditioning units run above ceiling, never inside the underfloor trunking. The nature of underfloor trunking installation make it very difficult and messy to extend. You need to hack the concrete floor to install additional runs and that can disrupts the operation of the whole floor. So only the wiring for the final circuits to the office work desks are run inside them. They are dedicated only for this purpose most of the time.

Usually some general-purpose power sockets are still provided on the walls even where underfloor trunking system is used. These sockets are usually run in the above ceiling trunking and a dropper conduit is used to make the connection to the sockets on the walls.

The lighting wiring are always run inside the above ceiling trunking. A system of trunking and conduit is the dominant method for this wiring purpose in almost all office buildings.

From the above it is quite clear that a much larger number of wiring runs above tha ceiling than under the floor. So that is the reason the bottom entry trunking is much smaller than the top entry ones. In this case the bottom trunking from both DB’s can be joined and still use the same size to connect to the vertical access box.

Telephone DB
As for the telephone DB, the trunking does not need to run above ceiling to go to the sockets at the worktables. The top entry trunking is for the incoming multi-core telephone cable from the telephone riser shaft. All telephone final wiring cables run inside the underfloor trunking. Since this blog is about electrical matters only I will not talk too much on telephone works. That may be a topic for one of my new blogs.

Copyright Electrical DB pictures

Monday, December 28, 2009

How to install fire stops

The following provides sample specifications and it presents a guide on how to install fire stops inside buildings. During the installation work of electrical services inside buildings especially cables, cable sleeves, cable trays, conduit and trunking, walls and floors often need to be penetrated to allow for the route of these components to pass through.

After installation of a wiring trunking through a wall for example, the gaps between the wall opening and the trunking need to be sealed back. Where the trunking passes through fire compartment walls, it is also usually the requirements of the Fire Department that the inside of the trunking be sealed properly to prevent fire smoke from traveling between adjacent fire compartments.

The same applies to cable sleeves. The gaps between the cables and the pipe sleeve should also be properly applied with fire stop materials to form an effective fire barrier of the same fire rating as the wall being penetrated.



To supply, install and test a fire-stopping system that comply with the requirements of the Electricity and Gas Supply Board, and in accordance with the contract Documents.


1.Firestop Compounds.

2. Damming Material.

3. Site Tests


Prior to commencement of the work, the contractor is required to submit the following:

1. To submit shop drawings, product data and manufacturer’s installation instructions for all materials and prefabricated devices, providing descriptions sufficient for identification at the job site.

2. To submit shop drawings showing proposed material, reinforcements anchorage, fastenings and method of installation. Construction details shall accurately reflect actual job conditions.

3. To submit Material Safety Data Sheets with product delivered to job site.

4. Previous Installation Records.


1. The installation of the fire stop system should conform to requirements of qualified designs or manufacturer approved modifications, as supported by engineering reports.

2. The installation of the fire stop materials and systems shall fulfill all the requirements specified by the contract Documents and meet all requirements of the Electricity and Gas Supply Board.

3. The contractor shall submit manufacturer’s product data, letter of certification, or certified laboratory test report that the material or combination of materials (fire stop system) meets the requirements specified as and in accordance with the applicable referenced standards.

4. The manufacturer of the materials should have been actively engaged in the manufacture and installation of fire stops for at least 10 years.


List of acceptable manufacturers:

1. Promat; 2. KBS; 3. Cape Durasteel; or other approved equivalent.


1. Fire stop compounds should be provided for caulk, pour, trowel or pump application. Material must be capable of sealing openings around single or multiple ducts, cables, wire or conduits against fire, smoke and toxic gases, and maintaining rating with a thickness no greater than the structure.

2. The fire stop compound should not contain any solvents or inorganic fibers. The penetration seal material must be unaffected by moisture and must maintain the integrity of the floor or wall assembly for its rated time period when tested in accordance with the requirements of Electricity and Gas Supply Board or ASTM E814 (UL 1479). The system should have a classified rating of up to and including 3 hours.

4. The fire stop system shall consist of a material, or combination of materials, to retain the integrity of fire-rated construction by maintaining an effective barrier against the spread of flame, smoke or gases through penetrations in fire-rated barriers. It will be used in specific locations as follows:

i) Penetrations for the passage of duct, cable tray, conduit, and electrical busways and raceways through fire-rated vertical barriers (wall and partitions), horizontal barriers (floor slabs and floor/ceiling assemblies), and vertical services shafts.

ii) Locations shown specifically on the design drawings or where specified in other sections of these specifications.

iii) Damming material, shall be provided where required as per manufacturer’s recommendations.


1. The fire stop materials or systems should be flexible enough to allow for normal movement of building structure and penetrating items without affecting the adhesion or integrity of the system.

2. The materials used should not require that the disposal of used containers be carried out as a hazardous waste.

3. The fire stop materials used should not use solvent materials that will free itself resulting the fire seal shrinking with time.



1. The materials should be delivered to site in original unopened containers or packages bearing the manufacturer’s name, brand designation, product description and U.L. classification mark.

2. The delivery of the fire seal materials should be coordinated with scheduled installation dates so that the storage time at the construction site can be minimized.

3. All materials should be stored under cover and be protected from weather and damage in compliance with manufacturer’s requirements.

4. The contractor should comply with all safety procedures, precautions and remedies as recommended by the manufacturer or the existing bylaws applicable to handling of any hazardous materials if applicable.


1. Prior to commencement of work, examine the areas and conditions under which the work is to be performed. Notify the main Contractor in writing of conditions detrimental to proper and timely completion of the work.

2. Ensure that each opening is of a proper size and in a suitable condition for the application of the fire seal. Sometimes the gaps or opening to be sealed is too large for the materials to be applied simply and some form of reinforcements may be required. Guide and instructions from the manufactures should be strictly followed in these cases.


1. The substrate should be properly cleaned and rid of dirt, dust, grease, oil, loose materials, rust or other matter that may affect a proper application or adhesion of the fire stopping materials.

2. Metal and glass surfaces should be cleaned with non-alcohol solvents.


1. All fire stop material should be installed in accordance with the design requirements and the manufacturer's instruction.

2. All openings, voids or holes resulted from the penetration for the electrical and mechanical services should be properly and completely sealed to form an effective barrier against smoke, water and air.

3. Certain sections of the project specifications may require that certain locations and parts of the work be installed with fire seals. It is the responsibility of the contractor to identify these locations and parts, and to coordinate with other trade contractors related to those parts of Work in order to provide a uniform system of fire stopping.

4. The installation work of the fire stop materials should be coordinated with other trade contractors so that the installation can be carried out after completion of the floor penetration but before covering or concealing of the openings commences.

5. When the ambient temperature of the surrounding exceeds the manufacturer's recommendation for installation of a specified fire stop material, then the installation must not proceed.

6. It is not the intention of a fire stop system to re-establish the structural integrity of a structure. The contractor should consult with the Engineer before coring or penetrating a load bearing structural assembly.

7. Fire stop systems are not designed to support live load or traffic. The contractor should consult with the Engineer if there is a reason to believe that these limitations may be violated for any reason.


1. A cable pipe sleeve should be installed with the inside diameter large enough to accommodate the intended cable diameter.

2. Fire stop materials should be applied at each end of the pipe sleeve in such a way as to comply with the requirements of a U.L. approved or the requirements of the Electricity and Gas Supply Board.

3. Insulate pipes on each side of a wall and caulk all around the insulation at the joint of wall and insulation.


1. The sleeve for the generator exhaust pipes should be properly installed and with the diameter large enough to accommodate the insulation thickness of the pipes.

2. The fire stop material should be installed in such a way as to comply with a U.L. approved system or to the requirements of the Electricity and Gas Supply Board.


The following visual inspection shall be carried out at each location that has been applied with fire stopping materials:

1. Only appropriate and suitable materials are used.

2. The fire stop materials should be continuously applied around all ducts or cables to for a complete and effective seal.

3. Proper adhesion of the fire stop materials to cables and ducts.

Copyright - How to install fire stops

Electrical generator site tests

Upon completion of the site installation work for the standby electrical generator, the generator should be tested again to ensure that it is working properly. There are always some possibilities that some damages have occurred to the electrical generator during transporting process including loading and unloading. Also some damages may have happened during the storage at the construction site and during the installation work itself.

The following tests need to be carried on the permanent installation of the unit. The manufacturer of the generator should send their representative to do the tests. A report recording each item of the testing shall be certified by the manufacturer and submitted to the Engineer.

All calculations to derive performance data shall be made strictly in accordance with formulae given in the relevant standards. Any alterations or deviations from the relevant standard test layout or formula shall be subject to the prior approval of the Engineer.

The formulae used for correcting test results to site conditions shall be subjected to the Engineer's approval and be given with the test results together with calibration details of any measuring instruments.

A. Diesel Engine

a. The set shall be started and run from cold in the presence of the Engineer and loaded to its full load shop rating in the minimum time stated in the Schedule of Technical Data.

b. Thereafter the engine shall be kept at 50% of the full load (FL) current and 85% FL for 11/2 hours each, and then at its full rated output continuously for a period of 5 hours followed by a 10% overload run of 1 hour duration.

c. The following functional cheeks shall be undertaken during the tests, including but not limited to:-

1. The ability of the starting system to perform in accordance with the specified requirements.

2. Uninterrupted continuous operation at the loads stated earlier.

3. The correct functioning of the over speed safety devices.

4. The ability of malfunction protection and warning devices to respond correctly to the fault conditions under which they should operate. For example, low lubricating oil pressure, high lubricating oil temperatures, high coolant temperatures, etc.

5. The dynamic and steady characteristics of the governing system in accordance with BS 5515. This shall include the full load rejection test, speed droop test at 20% load reducing from full load to zero load and over speed test.
6. The functioning of all automatic pressure and temperature control.

B. Engine inspection after tests

The Engineer reserves the right to request the Sub- Contractor to strip the engine for examination and selected parts for inspection without cleaning and exactly as taken from the engine. Any part examined by the Engineer and deemed needing replacement shall be replaced by the Contractor without any additional cost.

C. Leak test

The storage tanks shall be subjected to a test pressure of 0.66 bar ( 10 psi ) for a period of 1 hour on site to the approval of the Engineer. Compressed air or dry nitrogen may be used for the pressure test. It is not permissible to use water for on-site testing.

All piping after installation shall also be pressure tested to 15 bars for a period of one hour during which the leakage shall be zero.

D. Alternator

a. Visual inspection


Terminal marking, rating plate and danger signs.

Finishes, lifting lugs, etc.

Mounting of engine and generator set.

Cabling system.

Earthing and terminating arrangement.

Lubrication system

Sleeve bearings (where applicable).

b. Dielectric test

c. Insulation resistance test.

d. Functional (Sequence) Test

Operation of AVR

Operation of neutral earthing switches.

Operation of all indicating and metering devices.

Operation of all alarm devices.

e. Noise level measurement

f. Angular velocity (rpm) check

g. Phase rotation check

Copyright Electrical generator site tests

Wednesday, December 23, 2009

Temporary site floodlights

Large construction sites usually need temporary floodlight towers (in addition to the temporary lighting inside the new buildings) to provide lighting efficiently for the general movement, safety and security on the external areas of buildings under construction.

xxxxxxx RELATED PICTURES: High mast flood lightingTemporary lighting installation   xxxxxx

The lighting towers will usually takes the form of fixed tower or mobile tower units. Which one to use usually depends on the siting positions available for the lighting tower units and the duration of the contract.

For contracts with construction periods of relatively short durations, it may be much more economical to use mobile tower units.

However, if contract period is long, then it may be worth some considerations to use fixed height tower units. In any case, the fixed height towers can still be reused on future projects.

Careful dismantle the fixed height static towers at the end of the contract. Then the only extra materials that are required in at the next construction site is the foundation.

Static floodlighting tower units are normally available up to 18 meter high. They can be powered from the mains supply and they can be provided with their own electric generator.

The external areas of a construction site usually need a lighting level of around 20 lux average. This is the level sufficient of for the handling of construction materials and site clearing works.

A rectangular area of 60 meter by 60 meter can be lighted up to this light level by a typical 18 m tower carrying four units of 400 watt high pressure sodium fittings.

A main contractor with larger contracts and relatively longer contract period may want to consider a more elaborate study on their site lighting requirements.

If there is enough space to mount these floodlighting tower units, a proper lighting engineering study can be carried out together with the overall temporary electrical installation. The exercise would employ the floodlight lamp data, the aiming angles of the light fittings, and the mounting heights of the individual fittings to arrive at the required overall Illuminance.

These static towers would normally employ high intensity luminaries and with the type of equipment available today, the contractor can now light areas to sufficient level so the works can continue in evenings of the darker months. This is significant because it can considerably reduce the contract time.

Light fittings used in this application would necessarily be high intensity discharge type and the high pressure sodium lantern have become the more dominant type due to its high lighting output per kW of power usage (approximately 125 lumens per watt). A tungsten halogen lamp would give only 22 lumen per watt. The capital cost of opting the hight pressure sodium equipment is considerably higher than the tungsten halogen, but the main contractor may do well to consider other factors also such as the running cost, installation cost and the lamp life.

At the end of the construction work, all these equipment except the tower foundation, can be dismantled and transported to other project sites for reuse.

Below is a picture of a small mobile floodlight unit:

Picture 1 - Mobile site floodlight unit

Read more on site electrticity at this post, Temporary Electrical Installations.

There is also more imformation on temporary lighting at this post, Temporary lighting installation.

Copyright Temporary site floodlights

Temporary electric supply

What is a temporary electric supply?

A temporary electric supply is normally associated with the temporary electrical installation of a construction site. The term ‘temporary’ brings up a vision of a length of a length of twin and earth cable, or a four-core twisted cable and an undersized green earth wire, that is connected into a 30A single or 4-phase and neutral switch-fuse, trailing across the rough ground of the construction site to terminate into a seasoned self-fabricated distributed (with or without metal-clad enclosure).

On the so-called ‘distribution board’, a length of three flexible extension cord is connected to a clumsily assembled socket outlet with or without the use of a three-pin plug. How would you connect a three-core extension cord to a three-pin 13 A socket outlet? Somewhere on this blog, you can see clearly how it is done. It even has had various ways of doing it.

The extension cord run at high level near the soffit of floor slab, or some just run an the scattered floor to a temporary metalclad 13A switched socket outlet some 30 meters away.

The construction contract cost hundreds of millions, but the temporary electric supply system has been ‘engineered’ to fulfill all the site electrical requirements for the minimum price possible.

The main contractor has the responsibility to ensure the temporary electricity supply system installed is not only functional and meets all his electrical needs, but also safe for all involved in the construction work. The supply system need to be good enough to provide reliable power distribution, whether that period of the construction contract is three months or three years. Or whether the site supply requirement is 4 kVA or 3-megawatt supply.

What specifications to use for the temporary electric supply equipment?
Generally, what applied to low voltage installation is in the IEE Wiring regulations also apply to the temporary supply system. However two more British standards should be used to cover the gaps not covered there: BS 4363 (Specification for distribution units and electric supplies for construction sites and building sites) and BS 7375 (Code of practice for distribution of electricity in construction and building sites).

Source of the temporary supply

The temporary electric supply can be obtained from either the distribution network of the local electric supply authority or an independent electric generator installed at the site. Which one to use is usually just a matter of judgment on the cost involved.

However a few other factors may also need to be carefully considered which include practical problems that are usually associated with the distribution of the electric power safely and effectively throughout the site.

If the supply is taken from the local electric supply authority, a lead-time is usually required, as the authority would need time to arrange for the connection. The main contractor also need to submit sufficient details on the peak demand that will be required during the course of the contract, the positions of the point of supply intake and also the estimated contract period.

The authority usually requires enough details on the types and size of electrical load, e.g. lighting, heating, motors, etc. Motor loads usually need more details such as types of motors and the method of starting (direct-online, auto-transformer starting, etc).

Copyright Temporary electric supply

Tuesday, December 22, 2009

Mill lighting installation

The following lays lout some requirements for a palm oil mill lighting installation.

LIGHTING FITTINGS – include office, canteen, workshop and guardhouse

High-pressure sodium vapour lamps, high-pressure mercury vapour lamps, fluorescent lamps and incandescent bulkhead fittings shall be used for the general lighting within and outside the mill building. The Contractor shall submit copies of the brochures of the type and make of fittings to be supplied together with the tender documents.

For the main mill building 250W sodium vapour lamps and mercury vapour lamps are to be used for the general lighting. The 250W high pressure sodium vapour lamps shall be installed in the critical areas like the sterilizers, over the threshers, press platform and clarification station where there is a large amount of steam. These sodium vapour fittings shall be of the totally enclosed angle type fitting suitable for installation on the columns or walls of the building similar to Phillips type SNF 003 or equivalent. Where the fittings are to be installed on the outside wall of the building, these shall be of the weatherproof type suitable for tropical conditions.

In the other areas of the mill, 250W high pressure mercury vapour lamps similar to Phillip type HNT 003 or equivalent shall be installed on the columns or walls to provide the general lighting. These fittings shall be totally enclosed angle type suitable for tropical conditions c/w ballast and capacitor.

Some of the sodium vapour & mercury vapour lights within the mill and all the lights outside the mill shall be controlled by photocells and 10A switch at the individual subboards. These lights will automatically light up when it is dark.

Fluorescent fittings (2 x 36W) shall be installed under the platforms and over certain machinery to improve the general lighting in these areas.

Along the inclined empty bunch conveyor, the general lighting is to be provided by 60W incandescent bulkhead fittings installed on angle iron supports along the catwalk. The Contractor shall include the cost of the angle iron supports in the cost of the fittings.

Lighting for the Raw water treatment plant, effluent pump house and palm oil storage tank station shall be provided by 1 x 36W fluorescent lamp.

All fluorescent lamps supplied shall have a choke, starter and a capacitor housed within the fittings.

The light fittings for the compound lights shall be 250W high pressure Sodium vapour lamps similar to Phillips type SRC 511/250 installed on steel poles of not less than 8 meters in length. The steel poles shall have a diameter of not less than 150 mm at the base and shall taper to the top where the diameter of the top section shall not be less than 100 mm. The control gear of the light fitting shall be housed within a weatherproof compartment at the base of the pole. This compartment shall not be less than 500 mm from the ground. The choke, ignitor, capacitor and control fuse for each light fitting shall be installed within this compartment. Each pole shall be planted at a depth of not less than 1,500 mm deep.

The lighting around the fruit-loading ramp shall be provided by 400W high pressure sodium vapour lamps installed on 8 meter galvanized mild steel poles. These poles shall be suitably positioned to provide the best lighting and shall be positioned such that it is least liable to be damaged by the trucks. The lights shall be controlled from the lighting board (LDB-1) at the Sterilizer station by switches installed near the ramp.

The position of all light fittings shall be determined on site by the Engineer.

Copyright Mill lighting installation

Friday, December 18, 2009

Schools electrical installation

Electrical installation design for schools should be simple and economical. It must also be practical and functional.

Among the educational buildings, primary and secondary school buildings are the most common. Yet their numbers are still insufficient to cater for the high increase of enrollment throughout the country.

The construction of new school building by the education ministry has been increasing at a very high rate in the last few years. The design of the electrical system stresses more on the functionality and practicality of the system. The fundamental concept of the design is to ensure maximum safety and to keep maintenance requirements to the minimum. That also means that spare parts that will be needed for maintenance throughout the life of the installation should be easily obtainable locally and low-cost.

Other than the primary and secondary school building, the educational institution has the higher learning institutions such the universities technology institutes polytechnics, teachers training colleges and youth skills training centers.

These institutions have other criteria that set them apart from school building as educational buildings. In designing the electrical installations for these buildings, other that the factors of safety and functionality, special considerations should also be given to the factors of aesthetic values and the possibilities of future extension of the campuses or the building complexes.

Usually educational institutions like these consist of many separate large buildings like the administrative block, the staff quarters, the student hostel blocks, academic buildings, libraries, lecture theaters, halls and lecture halls. A few substations are usually required and they are usually located at large load centers throughout the campus.

These types of educational institutions usually have large campuses where many individual building are located far apart. As a consequence the electrical distribution system requires the use of higher distribution network. Proper switching arrangement between the various substations is usually designed for to ensure the continuity of supply and also to allow for ease of maintenance on the installation network.

A certain arrangement may also be worked out with the electricity supply authority regarding the design of the distribution and provisions of separate individual meters (which are separately billed by the electricity supplier i.e. canteen operators and retail shop operators) at certain facilities on the large campus.

Copyright Schools electrical installation

School lighting installations

The design of electrical installation, including lighting, for schools always have the following few factors as the fundamental design criteria:

1) Simple design

2) Low construction cost

3) Simple operation

4) Low maintenance cost

5) Easily obtainable spare parts

In lighting design for buildings, school lighting designs takes this factors to full use.

Most school buildings are used only during the day and throughout the year we have very bright days in this country. Apart from that, the architectural layout of most school building usually end up being provided with wide area of windows and long narrow corridors.

Due to these factors, the contribution of daylight has a considerable effect in the lighting design for school buildings. In fact the above factors should be utilized fully to obtain a maximum reduction in the number of light fittings that are needed to provide the necessary level of brightness at all time.

An optimized design can have a considerable impact in terms construction cost saving and will result in an installation that is simple to operate and with a reasonable degree safety, considering that the majority of occupants in the school are young children.

The most widely used types of light fittings in school buildings are the fluorescent types, and the most popular of them is the bare channel fluorescent type. This type has always been found to be the most suitable and economical choice for interior lighting.

Fluorescent lights have a good color rendering characteristics. They have longer life and are less susceptible to voltage fluctuations. They also has higher luminous efficacy (higher light output per watt of electricity consumed) than tungsten filament lamp, the nearest contender in terms of simple design and low construction cost.

Lighting installation for student hostel buildings more often utilize compact fluorescent fittings in combination with the conventional fluorescent tubes. This is because the compact fluorescent lamps can be blended easily with decorative luminaries while retaining most of the other advantages: energy saving, high light output per watt consumed, generate low heat and longer life.

In study bedrooms, maximum amount of light is needed over the study table while the room needs to have a feeling of warmth and comfort. Therefore this type of rooms have the compact fluorescent as the general lighting, and an adjustable desk lamp as the task lighting for the study tables.

Spaces with high ceiling like the multipurpose halls and gymnasiums need the type of lighting that require minimum maintenance. Therefore the popular practice is to use high performance lighting types of high pressure discharge lamp. The high performance criteria is very important here because the lamps not only need to be of high light output and less maintenance, but also need to have a good color rendering index because of the type of activities that are carried out in these building spaces.

The stages in multipurpose halls are provided with stage lighting which comprise of the fresnel spotlights, profile spotlights and cyclorama floodlights. The stage lighting luminaries are suspended from specially designed lighting barrels with a complete rigging system.

The stage lighting and the hall general purpose lighting are provided with separate controls. The stage lighting itself is provided with dimmer and programmable controls.

School complexes with student hostels and staff quarters are provided with road lighting along the access roads to the hostel and quarters buildings. The residential compound and carpark areas are also provide with suitable compound lighting and carpark lighting.

Copyright School lighting installations

Electrical rooms design

During the design of electrical installation for buildings, the spaces required as electrical rooms need to be provided for very early in the planning and design stage. Failure to do so would cause difficulties when the designers start producing their detail designs.

Types of buildings electrical supply needs

Two (or sometimes three) sources of electricity are normally required in high-rise buildings:

1) The normal mains supply from the electric supply authority or the local electricity supply company in some countries.

2) The standby or emergency supply for the standby electric generators. In most situations this supply is not an option, but a mandatory requirement for buildings that exceed a certain size.

3) The uninterruptible power supply, or commonly called UPS. This is only needed in certain types of office buildings and in some hospital buildings.

The choice of the supply voltage levels from the supply authority

The normal mains supply taken from the authority may be taken at HV (high voltage, normally 11 kV in this country), or LV (low voltage, 415 Volt, three-phase four-wire).

Whether it is LV or HV depends on the size of the maximum electrical demand to be expected of the planned building when it is in full operation.

It also depends on the effects of voltage drops and the level of voltages that are currently available from the supply authority.

Supply authority’s HV switch-room

When the incoming supply is HV, the authority usually only require a HV switch room to be built and handed over to them. This is where they house their high voltage switchgears and other equipment.

The location of this room must allow for easy access by the authority’s maintenance people and it should not present inconvenience to the occupants of the buildings or disrupts the building’s normal functions and operations.

Electrical distribution cables from the authority’s distribution network in the area will tapped and looped to the HV switchgear panels in this room. A series of panels are usually installed by them here.

Then from one of the HV panels, a supply feeder cable will be laid and connected to the consumer HV room and the HV energy meter.

Supply authority’s 11kV/.41vV transformer room

Often during the negotiations for the application of the supply, the authority may require that a transformer room is also provided and handed over to them together with the HV room.

Usually this happens when there is no suitable site available for their substation in the vicinity. This usually happens when the planned building site is at a congested area of towns like the city center.

Consumer HV room

As mentioned, the HV feeder cables that will carry the electric current to the planned building will need to connect to the consumer’s HV switchboard in the consumer HV room.

Part of the cost born by the authority in order to give supply to the new building are usually charged to the consumer (in what is usually called a “contribution fee”) and need to be paid before the authority commence their installation work.

Therefore, the nearer the consumer HV room is to the authority HV room, the shorter the HV cables that need to be laid and the lower the cost of the cables that need to be shared by both parties.

So in many cases, the consumer HV room needs to be nearer to the authority’s HV room.

Transformer room

Other than the HV room, the consumer also needs a transformer room, the LV room and the standby generator room.

When a large UPS supply is used, then a UPS room may also be needed.

The consumer transformer room and the LV room need to be as close to each other as possible in order to minimize the voltage drop.

For every meter of extra distance between these two rooms, a significant cost needs to be spent to overcome the voltage drop to an acceptable level.

Incoming supply at Low Voltage

If the supply taken from the authority is LV, then the supply authority will require a HV room and an transformer room to be provided.

The two rooms must be situated adjacent to each other although sometimes they accept that the HV switchgear and the transformers share the same room to save space.

The consumer is also required to provide a main switch room adjacent to the transformer room. The standby generator room also needs to be near the main switch room.

The locations of the electrical rooms

The location of the electrical rooms is also a major factor in the design of all types of electrical installations.

There are a few major requirements that must be taken into account when deciding on the locations for these rooms.

1) They should be located inside the buildings, as near as possible to the load centers.

2) The rooms should be as near as possible to each other.

3) They need to be accessible by maintenance vehicles and maintenance people for purposes of installation, operation and maintenance works.

4) They should be accessible by heavy vehicles during installation and when replacement of heavy equipment is necessary.

5) They should be adequately ventilated.

6) They should be adequately secured from possible disasters like flood, or even vandalism.

The above electrical rooms are in the category of substation rooms.

These rooms can actually be located at a separate building adjacent (or hidden behind) the main buildings.

However, there are still number more rooms that are needed by the electrical installation.

Other electrical rooms

1) Electrical service ducts or electrical risers. These service dusts are used to house the vertical submain cables that carry 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 located in these vertical ducts.

2) Individual floor electrical rooms. Each individual floors of significant size will usually need at least one dedicated electrical room to house the electrical distribution equipment for that floor.

However, sometimes the vertical service ducts may be able to fulfill these functions in which case a separate electrical room may not be necessary.

The architect may need to make these service ducts (sometimes also called “riser rooms”) bigger to give them enough space for proper operation.

The electrical rooms at each floor house the DB (distribution boards) that serves the final circuit wiring. Therefore, they should be as close as possible to the load center of the area that it serves.

Very tall buildings

If the planned building is very high (let’s say a 40 storey office building), or in cases where heavy loads are located at higher levels of the building, it may be necessary to provide substations at the higher levels of the building.

For the 40-storey office building, an 11/.415 kV substation may be necessary at one of the upper floor. It may be located at twentieth floor, for example.

All the substation room spaces as explained earlier will then need to be provided.

The floors of this substation will need to be designed by the structural to handle the loads of all the substation equipment.

Coordination with other design consultants and engineers

The above requirements need to be planned for at the early stages of the design and coordinated with the architects and structural engineers.

In many projects, the room spaces and their locations as requested by the electrical engineers are subject to “negotiations” with the architects and structural engineers, not merely technical coordination.

Copyright Electrical rooms design

Light switches installation

The installation of light switches and other electrical parts need to take into consideration a number of factors. For light switches, the following requirements must be incorporated into the design drawings and the specifications.

1) The grouping of lighting luminaries into single control should be done in small groups or on individual luminaries. This should be arranged in such a way that unnecessary lights can be switched off while allowing sufficient luminaries to be operating efficiently to give the required level of light over the working space where the activities is ongoing. This is part of the overall effort to lower the operating cost and conserve energy.

2) Where group switching are implemented, clear identification should be provided near the switch to indicate the lighting area controlled by a particular switch. For example, if a switch controls a number of light fittings over the main entrance of a lobby, then a label indicating “MAIN ENTRANCE” should be provided at the switch.

3) Switches should be provided at accessible locations that are within the line of sight from under the light fitting controlled. Exceptions to this are usually enclosed staircases and corridors used by the general public. For these areas, the location of the switches is selected to prevent abuse or unintentional operation by members of the public. Control of lighting for these types of spaces should be done by someone who is in authority over the area concerned.

In many cases these switches are located inside locked electrical rooms. In more advanced designs, these lights are controlled by a timer or the building control system so the lights are automatically switched on and off without human intervention. A manual bypass switch is usually provided where automatic controls are implemented.

In those parts of the world where the climates are seasonal, some form of sensors (eg. daylight sensor) is also commonly utilized.

4) The grouping of the lights should be so arranged that they can be switched off parallel to the windows. This will allow the row of lights nearer to the window can be switched off when the effect of daylight from outside the building is already adequate for the activities in the room.

5) Further control in the levels of lighting should arranged by the use of alternate switching. For example, in a row switching arrangement, alternate luminaries in the same row should be grouped under the same switch. In this way it is possible to switch off half the lights (thereby reducing half of the energy consumption) while maintaining a reasonable uniformity at the same time.

This method can be taken further by arranging the grouping to give a three or four lighting levels. For example, the corridor lighting at hospitals can be arranged into three alternate switching groups. After 7 pm one of the three groups of lights will be switched off, reducing the energy consumption by all corridor lights throughout the hospital by one third. That is a significant amount of kWh for large hospitals.

After midnight, the second group of lights will be switched off, reducing the consumption by a further one-third. That means after midnight only 33 percent of the corridor lights will be “ON”, and these lights are one of three alternately throughout all the corridors.

Copyright Light switches installation

Emergency lights installation

The installation of self contained emergency lights is a statutory requirement in most countries. They need to be provided at strategic places throughout the building in order to aid the evacuation of the building occupants out of the building in the event of failure o the mains supply.

The need for these emergency lighting is real even during daytime because some internal corridors inside the building are actually too dark without some form of lighting. The emergency lights are meant to provide the minimum illuminance needed for a safe and orderly movement of the people.

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).

The exact quantity and the exact locations of these emergency light fittings are usually recommended by the Fire Department. In practice, a licensed architect is required by law to submit the building design plans to the Fire Department for approval before the building construction commences.

The architect would need to incorporate these lighting into their fire protection design schemes in order to obtain the Fire Department’s approval.

This layout is part of what is normally called the “static fire protection”. Those services like the wet risers, etc are called active fire protection and they will need to be submitted by licensed professional mechanical engineers to the Fire Department after the passive fire protection schemes (submitted by the architects) have been approved.

Prior to the submission by the architect, the electrical engineer’s input may be requested by the architect with respect to the quantities and locations of the emergency lights. However this task has become so routine that the engineer’s advice on this aspect is rarely necessary.

After the approval has been obtained, the approved layout of the emergency lighting is binding and it has become an input and a minimum design requirement for the electrical engineer. She can add more of the emergency light fittings into the design, but she cannot omit or change what has been approved in the submitted drawings.

That is basically the principle.

In addition to the self contained emergency lights that are required by the fire department, some of the general lighting luminaries are also connected to the essential supply that has been backed by the standby generator. This is sometimes done to supplement the lighting provided by the self contained emergency lights.

More often, however, this is done to provide some level of general lighting that can allow normal work to continue even in the event of normal power failure. Of course power failures caused by fire conditions demand a different course of actions immediately from all the building occupants.

There is one more lighting component that is closely related to the self contained emergency lights, that is the “EXIT” sign.

The Exit signs are also required by law similar to the emergency lights. They must be provided at all exit doors of all buildings and all floors, and at each location where the fire emergency exit routes change direction.

Similar to the emergency lights, these components are included in the proposed static fire protection submitted by the architects to the Fire Department.

An approved layout of this fire component will become a minimum design requirement to the electrical engineer. She can add more of the lighted Exit signs, but she cannot reduce them or change them.

Like the emergency lights also, the Exit signs are self-contained, battery operated. The difference between the two is that the Exit signs are always on.

See pictures of electrical installations by visiting this post, Free electric installation pictures.

Copyright Emergency lighting installation

Temporary lighting installation

A construction site’s temporary electrical installation must also provide adequate lighting for the activities that are carried out at a particular workspace whether indoor or outdoor. Arguably more important than the light levels, the temporary lighting installation should be sufficiently safe for use and provided with adequate protection to prevent electrical shocks.

xxxxxxx RELATED PICTURES: High mast flood lighting | Temporary site floodlights  xxxxxx

1) Wire cages to prevent against mechanical damage should protect temporary light fittings at the construction sites. Damaged light fittings not only result in the repair cost, but they also present risks of electrical shocks to workers using them or those who are nearby. Precautions must be taken against the danger of electrical fires that because of damaged light fittings or the temporary supply wiring.

2) The temporary wiring supplying the lighting circuits should be connected to the special lighting section on the temporary switchboard. These circuits should be protected by 100 mA RCD (residual current circuit breakers).

3) Festoon lighting should only be used strictly in underground shafts, wells and tunnels. When this type of lights are used, the lamp holders should only be the moulded-on, non-removable type (the lamp holders are bonded or moulded to the wiring cables) and the lighting supply voltage is 32 Volts or below.

4) Either the temporary wiring or the newly installed permanent wiring may supply lift shaft temporary lighting. However, the light fittings used should be properly guarded against accidental mechanical damage and they should only be connected to the wiring using a lighting plug and socket. These lights should be installed at intervals of less than nine meters along the vertical length of the lift shaft. The control of the lift shaft lighting should be by means of two-way switches located near the shaft access points.

5) Normal duty lighting circuits are installed to provide general illumination for work and allow safe movement inside and around the construction site.

6) The installation of wiring for the temporary lighting should be carried out with proper supports and fittings to allow for wiring cables to be routed in ways that minimize obstructions, which can results in damage to the luminaries and wiring. These damages can present shock risks to the works and possibilities of electrical fires.

7) The use of lighting circuits supplied at safe extra low voltage levels (SELV - voltages less than 50 volts ac or 120 volts dc) is highly recommended for working in confined spaces where workers faces high possibilities of frequent contacts with temporary electrical equipment and wiring.

8) An illumination level of 10 lux is adequate for general movement within a building under construction. As an illustration, one length of 100 meter festoon light string fitted with 20 nos 100 watt lamps at 5 meter intervals will give a 10 lux over a rectangular area of 25 meter x 30 meter.

Read more on site electricity at this post, Temporary Electrical Installations.

You can also see a few pictures of site floodlight at this post,  Temporary site floodlights.

Copyright Temporary lighting installation

Thursday, December 17, 2009

Electrical MCCB installation

This section lays out the major performance requirements for the MCCB (moulded-case electrical circuit breakers) installation inside switchboards.

All moulded-case circuit breakers shall comply with IEC 60947-2.

All electrical MCCB shall be of moulded insulating material of good mechanical strength and non-tracking properties. The tripping mechanisms shall be calibrated in compliance with IEC standards at the factory and the breaker shall be sealed to prevent tampering.

The MCCB shall be so designed that when on tripped condition, the circuit breaker cannot be switched on unless it has been reset by switching it to the OFF position first. The operating condition (i.e. ON, OFF or TRIP) of the circuit breaker shall be clearly indicated. The construction and operation of the MCCB installation shall be such that if a fault occurs, all the poles of the breaker shall operate simultaneously to isolate and clear the fault efficiently and safely without any possible risk to the operator or to the installation.

Each MCCB shall incorporate a ‘trip-free’ mechanism to ensure the breaker cannot be held closed under fault conditions. The operating mechanism of the circuit breaker shall be hermetically sealed at the factory and all metallic parts associated with the operating mechanism shall be treated against rust and corrosion.

Bolt-in type solid neutral links shall be provided and fitted in the same compartment together with the phase poles.

Means shall be provided to padlock the MCCB in the ‘OFF’ position. Mechanical ‘ON/ OFF’ indicator operating in conjunction with the rotary type operating handle of the circuit breaker must be provided.

MCCBs supplying loads from switchboards connected to the emergency power system shall be provided with facilities for remote operation (OPEN and CLOSE) and auxiliary contacts for remote indication.

Copyright Electrical MCCB installation

Electrical ACB installation

This section lays out the major performance requirements for the ACB installation (electrical circuit breakers of the air-break type) inside switchboards.

Switchboard circuit breakers shall be of the air-break type suitable for indoor use and withdrawable complete with all necessary instruments, transformers, closing and tripping devices and protective instruments. They shall be easily accessible and operable from the front and provided with padlocking facilities. Both phase and neutral switching shall be required. Circuit breakers shall comply with IEC 60947-2 regarding their test performance and number of operating cycles, and shall have a rated short-circuit making and breaking capacity specified in the drawings and complying with IEC 60947-2 Table II. They shall be trip-free.

Locking facilities shall be provided on the ACB and control switch so that in any position the circuit breaker can be prevented from being directly and manually operated. Mechanical and electrical lockouts shall be provided to prevent closing of the electrical ACB after an over-current trip.

All operating mechanisms shall have mechanical ‘ON’ and ‘OFF’ indicators. ‘CLOSED’, ‘OPEN’ and ‘TRIPPED” indication lamps shall be provided. Hand charged or motor charged spring mechanism shall have mechanical indicators to show ‘SPRING CHARGED’ and “SPRING DISCHARGED’.

All ACB supplying loads from the main switchboards shall have motor charged operating mechanisms, which shall be arranged so that release of the spring to close the circuit breaker can only be done by deliberate action. It shall not be possible for shocks to release the charged spring. Remote controlled switching shall also be provided for motor charged operating mechanism ACB.

Closing and trip control switches shall turn clockwise for closing and anti-clockwise for tripping and labeled ‘OPEN-NEUTRAL-CLOSE’ with spring return to neutral.

The shunt trip coil shall be operated by 240 Vac supply unless otherwise stated in the design drawings.

All circuit breakers shall be provided with interlocks to ensure that:

a) a circuit breaker cannot be connected or withdrawn while closed;
b) a circuit breaker cannot be closed until they are fully plugged in or is completely isolated;
c) a spring charged mechanism cannot be discharged until it is fully discharged.

Mechanical and electrical interlocks shall be provided in cases where multiple incoming supplies are not to be paralleled. Tripping of a closed ACB shall not occur if an attempt is made to remove the trapped key or when it is in the withdrawn positions.

Facilities for operational tests of the circuit breaker shall be provided when in the isolated or withdrawn positions.

Provide auxiliary contacts for remote monitoring of all incoming and sectionalizing breakers as well as all distribution breakers on switchboards supplied from the emergency power system.

ACB used for distribution on switchboards supplied from emergency power system shall have provision for remote operation (OPEN and CLOSE) for load management.

All protective relays and instruments shall be provided as shown in the design drawings.

Where specified in the design drawings, the ACB shall have integral solid-state trip units with built-in over-current and earth-fault protection having time-current characteristics. A combination of the following time-current curve-shaping adjustments shall be provided:

a) Ampere setting
b) Long time delay
c) Short time pickup
d) Short time delay
e) Earth fault pickup
f) Earth fault delay

The solid-state trip-unit shall have a digital information system that provides circuit current values and mode of trip indication (i.e. overload, short circuit, and earth fault) with fault current levels displayed following an automatic trip operation.

All solid state trip units shall be provided with test jacks for in-service functional testing using a small hand-held test kit.

Copyright Electrical ACB installation

Electrical DB installation

The electrical DB (distribution boards) for high-rise office installations shall be non-ventilated, naturally cooled, metal enclosed type, flush fronted and suitable for front access and shall be built to comply with IEC 60439-1. All louvers shall be covered with wire mesh.

The distribution boards shall contain MCCB (moulded case circuit breakers), MCB (miniature circuit breakers), RCD (residual current devices) and busbars as indicated in the contract documents. The DB shall be suitable for wall mounting or floor mounting as appropriate.

All necessary fixing materials, mounting bolts, etc shall be provided for the type of mounting mentioned.

All operating devices shall be mounted for installation, cable termination and maintenance operation at the front of the panel.

All distribution panel located outside the riser and public area shall have key lock handle.

Enclosure and Degree of protection
The DB enclosures shall be fabricated from rolled steel angle sections and shall be self supporting when assembled, uniform in height and depth from front to back. Sheet steel used shall not be less than 2 mm thick, anti-rust coated steel plate.

The distribution board shall be rigidly constructed to be stand alone units without any possibility of sagging, deformation or warping.

The front covers of the DB shall be of hinged-door type. The front doors shall be provided with lockable push button type. The doors shall be arranged to seal onto the board frame by means of a non-perishable dust-proof material. The sealing material shall be synthetic rubber and not foam. Doors shall be effectively earthed to the fixed enclosure by braided straps. Cover bolts or nuts shall be retained in place when undone.

For all internal DB installation, the degree of protection for the DB enclosures as per IEC 60529 shall be at least IP 41. When the doors are opened, the degree of protection to all live parts shall be at least IP 20.

All the distribution panels shall have Form 1 construction in compliance with IEC 60439-1.

The incoming and outgoing cable entry on the distribution boards shall be protected with rubber material to prevent damage to the cables.

Selection of components
All components shall be standardized as far as practical and shall comply with relevant IEC publications.

Busbars for the DB shall be of plain hard-drawn, high-conductivity, electrolytic copper bars in accordance with BS EN 13601: 2002 and of adequate rectangular cross-section to carry continuously the specified current without overheating and shall be rigidly mounted on insulators so as to withstand any mechanical force to which they may be subjected under maximum fault condition.

The DB busbars shall be colored red, yellow, blue and black at appropriate points to distinguish the phases and neutral. No tapes shall be used.

Moulded case circuit breakers (MCCB)
Refer to the MCCB section for the details on MCCBs.

Type test certificates shall be produced for the MCCB selected from internationally recognized testing laboratories.

Miniature circuit breakers (MCB)
Refer to MCB section or details on MCBs.

Refer to Electrical DB Wiring section for details on the DB wiring.

Residual current devices
Residual current devices shall provided as indicated in the design drawings and construction drawings.

Refer to Protection, Metering and Control section for details.

Type test certificates shall be produced for the RCCB/ ELCB selected from an independent internationally recognized independent testing laboratories.

Finishing and painting
Refer Electrical DB paintwork section for details on finishing and painting of electrical DB.

Copyright Electrical DB installation

Electrical busbars

The electrical busbars inside the switchboards shall be of plain hard-drawn, high conductivity, electrolytic copper bars in accordance with BS EN 13601: 2002, and of adequate rectangular cross-section to carry continuously the specified current without overheating and shall be rigidly mounted on non-hygroscopic insulators so as to withstand any mechanical forces to which they may be subjected under maximum fault condition.

Busbars shall be colored red, yellow, blue and black at appropriate points to distinguish the phases and neutral. No tapes shall be used. The main busbars shall be arranged in a horizontal plane and in the order of red, yellow, blue and neutral phases from back to front. On each panel connections shall be red, yellow, blue and neutral phases from left to right viewed from the front of the panel.

The phase and neutral busbars should be located in the top compartments of the switchboard.

The busbar system shall be readily accessible for inspection, construction and maintenance duties without the requirement of additional equipment. In case of a busbar short circuit, it shall be possible to clean or to replace the busbars and the support system without stripping the assembly.

In the busbar compartment the phase busbars may not be fully insulated. However, each phase busbar shall be able to withstand at least an applied AC test voltage of 2.5 kV for a period of 60 seconds.

The droppers shall have full segregation by insulated materials. The insulation of the busbar jointing and branching points shall be of equal quality to that of the main bars and shall be removable and easily replaceable for inspection.

The neutral bar may be not insulated in the busbar compartment but shall be insulated at all other compartments with the same insulation level as the phase busbars.

The earth bar shall be located in the top or bottom compartment and in all cable riser compartment of the switchboard and shall be easily accessible. Sufficient connection points with adequate terminating facilities shall be provided for terminating the cable earth leads. The earth bar shall be sized complying with IEC 60439-1.

Copyright Electrical busbars

Electrical DB wiring

Following is a sample specifications for the wiring of an electrical DB. Refer the section on Electrical DB installation for specification details on the construction of distribution boards.

Photo 1 - Internal wiring of an electrical DB

Terminals for external conductors All conductor terminals shall be suitable for copper conductors.

All cable termination assemblies shall have facilities for entry of cables from both the top and the bottom of the distribution boards. Cable entries, cable clamping, earthing facilities and supporting devices that are provided shall be suitable for the type, size and number of the incoming cables.

The identification ferrules Both ends of each wiring conductor shall be provided with identification ferrules. The ferrules shall be made of an insulating material of a type not affected by oil or damp. The characters shall be suitably marked in black. (See photo here: Wiring identification ferrules)

The ferrules shall be of the continuous ring type. A slide-on type will not be acceptable. The markings shall be in accordance with the relevant manufacturer’s drawings.

The wiring cables The minimum allowable cross-sectional area of control cables shall be 1.0 mm.sq. Wiring cables with a cross-sectional area of 1.5 mm.sq or larger shall always be stranded. The secondary circuits of current transformers with a 5 A rating shall not be less than 2.5 mm.sq. Color-coding of all wiring shall be in accordance with IEC 60446. The color of earth wiring cables shall be green with yellow stripes.

Wiring between two terminals shall be continuous. Joints or interconnections at locations other than at terminals are not acceptable. All wiring cables shall be terminated at both ends at a connection terminal. As a minimum requirement, use shall be made of rail-mounted terminals (TS 32 rail assembly) of high-grade Melamine.

When different voltage levels are employed in a single DB enclosure, partitions shall be installed between the terminals of different voltages.

The wiring The wiring ends of stranded conductors which have to be connected into bus type of terminal contacts shall be provided with compression-type pre-insulated wire pins with insulation support.

When cable lugs are used, they shall be of a compression type. To accommodate and support the wiring cables, covered plastic trunking, channels, insulated tubes or plastic strips shall be used. Wiring cables shall never be mounted directly to a metal part of a distribution boards.

The space factor for channels shall never be less than 30 percent. Where supporting of a wiring cable is not feasible, the cable shall be as short as possible.

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 finishit.

Copyright Electrical DB wiring

Temporary electrical switchboards

All electrical switchboards used on temporary electrical installations or building construction sites should be of substantial construction. Where they are installed in outdoor locations, the switchboards should be so constructed that safe operation is not impaired by the weather. This weatherproof criteria usually means an IP rating of not less than IP 65. When the doors are opened, the degree of protection to all live parts should be no less than IP 20.

The method used for installation must have provisions so the cables and flexible extension cords coming in and out of the boards can be properly supported.

The temporary switchboards should also be provided with a door and locking facility that comply to the requirements of the electricity supply authority. Door should be designed and attached in a manner that will not damage any flexible cords connected to the board, and should protect the switches from mechanical damage. The door should be provided with a sign stating ‘KEEP CLOSED’ – ‘LEADS THROUGH BOTTOM’.

The switchboard should have an insulated slot in the bottom for the passage of leads.

The temporary switchboard should be attached to a permanent wall or other suitable portable structure, which has been designed for the purpose. Pole or post-mounted switchboards should be fixed by means of coach screws or bolted.

If the switchboard is used to supply other sub-boards downstream, every sub-board should be provided with a clearly labeled main isolating switch.

Temporary lighting outlets should be in a separate section on the switchboard and they should be clearly identified as lighting circuits. To protect from electric shock, the supply to the temporary lighting section should be provided with 100 mA residual current device (RCD), while the supply to the temporary socket outlets section should be protected by an RCD or earth leakage circuit breaker (ELCB) of sensitivity not more than 30 mA.

If too many tools are connected at the same that results in frequent tripping of the shock protection device, then the supply should splitted into multiple sections or multiple distribution boards, with each section or DB protected by a 30 mA RCD. This will prevent the shock protection device from being defeated by workers whose works have been most inconvenienced by the frequent tripping.

The electrical contractor or nominated persons should ensure that all power circuits are isolated or made accessible so as to eliminate the risk of fire, electric shock or other injury to persons after completion of the daily work.

All temporary supply mains should be protected by a circuit breaker or H.R.C. fuses.

A clearance of at least 1200 mm should be maintained in front of all switchboards and if the switchboard is located in a room, a clearance of 700 mm minimum should be provided around the other three sides. If the switchboard is also provided with rear access, then the rear of the switchboard must also have a 1200 mm clearance minimum.

Temporary switchboard should be so located that the maximum lengths of the flexible cords do not cause excessive voltage drops and impairs the normal operation of electrical equipment and portable electric tools.

The switchboard should be properly earthed and the color-coding of the protective conductors shall be done in accordance with IEC 60646.

A main earth bar should be provided inside the switchboard and it shall be connected to the temporary electrical grounding using appropriate size earthing conductor. The cross-section of the conductor shall be sufficient to carry the rated short-time withstand current of the switchgear.

All metal parts of the switchboard cubicle, and the metal parts of the components that are mounted on the switchboard including door, relays, instruments, etc shall be earthed through branch connections to the earth bar.

Frames of the draw-out circuit breakers (if they are used) shall be connected to the earth bar through a substantial plug type contact.

All temporary electrical equipment and switchgears including the switchboards should be inspected and labeled regularly by a licensed competent person before their first use and every three months thereafter.

The details of the inspection should be recorded in a logbook for inspection purposes. The details recorded in the logbook should include but not limited to the following:
a) Date of the inspection.
b) Identification no of the equipment or switchboard inspected.
c) License number of the inspecting competent person.
d) Any repair required because of the inspection.

Inspection label or sticker should be attached to the inspected switchboard showing the date of the most recent inspection. This label should carry the verification signature of the endorsing competent person.

Repair works that are required by the inspection should be carried out without delay. If the required repairs are related to safe use of the temporary switchboard, they must be properly carried out before the board is put to further use.

There is also a more detailed article on temporary electrical installation at this post, Temporary Electrical Installations.

Copyright Temporary electrical switchboard

Wednesday, December 16, 2009

Switchboard electrical earthing

Following is a picture showing the earthing busbar of a main switchboard. Below the picture is a simple performance specifications for the grounding of the switchboard.
The are also two more posts on switchboard installation check and switchboard electrical tests. The latter is a general list of tests and inspections that are usually required of a major switchboard such as main switchboards and large subswitchboards.
Photo 1 - Earthing busbar of a main switchboard (MSB)
The earthing of an electrical switchboard shall be in accordance with BS 7430, and the color coding of protective conductors shall be in accordance with IEC 60646.
Switchboard earthing busbar
The switchboard earthing busbar shall be installed internally along the full length of the switchboard. The material of the busbar shall be the same as the material of the phase busbars. (See more photos: Switchboard earthing busbar.)
Equipment earth bar
Where the substation consists of 11 kV switchgears, transformers and LV switchboards, earthing copper tape shall be installed continuously along the full length of the substation.
It shall be connected to the main system earth bar at both ends using appropriate size earthing bolts with nuts and spring washers.
The earthing copper tape shall be made of hard-drawn high conductivity copper.
The cross-section of the earth bar shall be sufficient to carry the rated short-time withstand current of the switchgear for the allowable temperature rise and the time specified.
Internal branch earth connections
The branch earth connections made from the switchboard earthing busbar to the individual switchboard components shall consist of adequately sized copper strips, or green/ yellow striped PVC sheathed stranded copper conductor.
The termination lugs shall be of the compression type.
Earthing of metal parts
All metal parts of a switchboard where live components (such as relays, instruments, indicating lights etc) are mounted shall be earthed through branch connections to the switchboard earthing busbar.
Doors of the switchboard shall also be similarly earthed.
Frames of the draw-out circuit breakers shall be connected to the earthing busbar through a substantial plug type earthing contact.
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.
Copyright Switchboard electrical earthing

Switchboard electrical tests

The following electrical tests must be carried to all switchboards, sub-switchboards, main distribution boards and motor starter panels.

A. Full type tests
1) Full type tests shall be carried out in accordance with IEC 60439-1, IEC 60947-1, and IEC 60947-6-1. Certificates issued by approved independent testing laboratories shall be submitted to the Employer’s Representative.

The type tests shall include the following:
a) Verification of temperature-rise limits
b) Verification of the dielectric properties
c) Verification of the short-circuit withstand strength
d) Verification of the effectiveness of the prospective circuit
e) Verification of the clearances and creepage distances
f) Verification of mechanical operations
g) Verification of the degree of protection

B. Routine tests
Before the product leaves the works, the manufacturer shall carry out the relevant routine tests in accordance with IEC 60439-1 on the total assembly, and the IEC 60947-1 and IEC 60947-6-1 parts thereof when delivered with time intervals, and the results shall be recorded in a test report.

C. Special tests
Carry out the special tests recommended in IEC 1641 Guide for Testing Under Conditions of Arcing Due to Internal Fault, the result shall be recorded in a test report.

D. Acceptance Tests at Manufacturer’s Work
a) Acceptance tests shall be carried out on the completely assembled switchboards and motor starter panels. Transportable units can be wired together for the purpose of the tests instead of completing the busbar joints.

b) The tests and checks shall include, but not limited to, the following.

c) All the switchboards and motor starter panels shall be visually inspected for technical execution and conformity with the latest issue of approved drawings and the latest issue of the relevant standards. Spot checks shall be made to verify the following:

1) Dimensions
2) The degree of protection of enclosures
3) The degree of protection within compartments
4) The effectiveness and reliability of safety shutters, partitions and shrouds
5) The effectiveness and reliability of operating mechanisms, locks and interlock systems
6) The insulation of the busbar system
7) The creepage distances and clearances
8) The proper mounting of components
9) The internal wiring and cabling system
10) The correct wiring of main and auxiliary circuits
11) The suitability of clamping, earthing and terminating arrangements
12) The correct labeling of functional units
13) The completeness of the data on the nameplate
14) The availability of the earthing system throughout the switchgears
15) The interchangeability of electrically identical components

d) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltage shall be at least:

1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac, with a minimum of 1500 Vac for 1 second.

e) Testing of the mechanical and electrical operation of a number of functional units on random basis, including their control and protective devices.

f) CT polarity, magnetization, ratio and burden measurements

g) Secondary injection tests

h) Primary injection tests

i) Painting and finishing tests:

1) Measurement of paint thickness.
2) Humidity (cyclic condensation) tests to BS 3900 Pt. F2. Painted panel shall withstand 1000 hours under test with no blistering of film and corrosion of base metal.
3) Adhesion test to ASTM D3359-02. Test tape shall not expose more than one 3 mm.sq of bare metal or underlying coating.
4) Impact resistance test to BS 3900 Pt. E7. Paint shall not chip off.

j) The manufacturer test shall be verified and witnessed by the Employer’s Representative or his representatives.

E. Site Tests
At the completion of the installation at site, each switchboard and motor starter panels shall be field tested by a representative of the manufacturer. A report recording each item of the tests shall be certified by the manufacturer and submitted to the Employer’s Representative.
a) Visual inspection
1) Correctness of location and mounting
2) Labeling, nameplates and markings.
3) Verification of torque for all nuts and bolts on busway.
4) Observation of cable bracing, both incoming and outgoing, certifying that it is in accordance with the manufacturer’s recommendations.
5) Safety shutters, partitions and shrouds.
6) Functional units, operating mechanisms, locks and interlock systems.
7) Mounting of components.
8) Internal wiring and cabling system.
9) Clamping, earthing and terminating arrangement.
10) Earthing system.

b) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltages shall be at least:
1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac with a minimum of 1500V for 1 second.

c) Power frequency withstand voltage test.

d) CT polarity, magnetization, ratio and burden measurements.

e) Secondary injection test

f) Primary injection test

g) Functional / sequence test
i) Operation of each disconnecting means under load
ii) Operation of each automatic transfer switch
iii) Operation of all alarm devices

h) Mechanical operation test
i) Operation of each disconnecting means under load
ii) Operation of each auto transfer switch
iii) Operation of all interlocks

i) Calibration and setting of protection devices

Copyright Switchboard electrical tests