Friday, April 16, 2010

Building’s electrical rooms layout

During the design of an electrical installation for a building, spaces that are required as electrical rooms need to be provided for very early in the planning and design process.

I will try to present this in a form of a few basic concepts so that non-electrical readers can benefit from it.

There are also a few diagrams at the end of this post, but I do want to go too technical here as this may turn off the non-electrical readers.

If you need a more technical discussion, I will send a few posts of electrical substation layout and design in future.

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RELATED ARTICLES: | Substation rooms layout diagram |  1600 kVA Transformer Pictures | Cable ladder pictures  | Electrical installation picturesFire Riser Rooms

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Sources of electrical supply

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 supplies, or commonly called UPS. This is only needed in certain types of office buildings and in some hospital buildings.

Voltage level of the incoming supply

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 the LV or HV supply 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.

Authority’s HV 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 the Authority’s HV room

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

(Separate meter room: At times, the local office of the electricity supply authority requires that a small meter room be provided and handed over to them. This is where they house the meter panel.)

Electrical distribution cables from the authority’s distribution network in the area will be tapped and looped to the HV switchgear panels in this room. They usually install a series of HV panels here.

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

Consumer HV room

A consumer HV room is generally a repeat of the authority’s HV room. The equipment and switchgears located in them are also similar.

The purpose of the consumer HV room is to house the equipment that are essential to the safe and proper handling of the electrical high voltage supply received from the authority’s HV room.

If the building management need to switch off the high voltage supply for some reasons, then this is where they do it.

Among the reasons may be if the transformer is faulty and need to be serviced ar checked.

Another reason may be if the transformer room is located at a separate location and the high voltage cables to the HV switchgear is by cables buried underground. Sometimes an excavation need to be carried out very close to the cable location that a complete shutdown to the supply carried by the cables is necessary.

The third scenario might be if the main low voltage switchboard (the electrical panels that receive the low voltage currents directly from the transformer) need maintenance or repair. Then the only way to make the main switchboard completely dead is by turning off the supply at the HV switchgears inside the consumer HV switchroom.

Can we turn off the supply by switching off the switchgears inside the authority’s HV room?

No, we can’t.

The room and all the equipment inside them are legally theirs now.

By transferring the HV electrical room to the authority, the building owner are actually required to sign some form of an agreement to transfer the ownership of the room to the electricity supply authority, or to lease it to them for a duration of 99 years I think.

It is like an embassy building in a foreign land.

Likewise, the supply authority is not allowed to freely access the consumer’s HV room or the equipment inside.


Metering CT

Buildings taking supply exceeding a certain amperes require the use of a set of CT’s (current transformers) in order to measure the energy consumption. The contractor of the new building will have to provide these CT’s.

However, the new CT’s also need to be sent for calibration and certification by the electric supply company before installation.

After the calibration, the CT’s are installed inside the consumer HV panels. A set of wiring are then installed to connect these measuring current transformers to the authority meter panel inside the meter room.

Authority’s transformer room

Sometimes during the negotiations on 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 of the area, such as when the planned building site is at a congested area of towns like the city center.

When transformer room(s) is required, the authority electrical substation would be a complete substation, not just a HV room.

This means that the substation may also be used to supply other buildings and properties nearby.

Distance from Authority HV room to 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.

In construction projects where the land space is limited such as building projects, it is highly recommended to locate the HV electrical rooms as close to each others for another reason.

Areas where high voltage equipment and cabling are installed need to be controlled as a restricted area. Locating the HV room near each other would make control easier and the restricted area would take less space.

Consumer’s transformer room, LV room, standby generator room and UPS 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.

LV room and transformer room to be as close as possible

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.

The cables used to carry the low voltage electrical supply also are usually of very large diameters.

Large diameter electrical cables are very difficult to maneuver and bend around corners and tight areas.

Keeping the two electrical rooms close to each other effectively reduces the bends needed of the electrical cables.

Supply intake at LV

If the electricity supply taken from the authority is LV (low voltage), then they will require a HV room and a 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 electrical transformers share the same room to save space.

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

However, if the electrical energy required by the building is less that about 300 KVA, no electrical room is required to be prepared and handed over to the electrical authority.

They will tap off the supply from a nearby existing electrical substation or tap it off from an existing low voltage distribution network.

It is for this reason that some property developers submit their application of electric supply in stages with each stage requiring not more than 300kVA.

All the above electrical rooms are needed so we can receive supply from the public mains.

However, there is the second type of electrical supply in a building operation, which is the standby generator supply. I will not talk about the third type, the UPS supply (uninterruptible power supply) today because only certain types of buildings use it. I will address that topic in a separate post.

Standby diesel generator room

As I said earlier, no building exceeding a certain size or a certain height is allowed to be operated or occupied without some form of a standby emergency power.

The “emergency” here means when the public electrical supply is suddenly not available.

It also means a fire situation because a normal electric cable would fail under fire and the fire fighting equipment would need “emergency” power so the firemen could use them.

Now, this standby diesel generator and all its ancillary equipment need a room to house them in.

However, the electric generator is a bulky and noisy machine. It also produces very strong vibrations that can be transferred to the building walls and structure.

Therefore, a room for this electrical generator need to be specially designed and the room location need to be purposely located.

If you are given the freedom to make a decision, make a small separate building to house this noisy electrical generator, preferable somewhere hidden behind the main building.

Then build up all other main electrical rooms that I described earlier around the generator room.

If you start that way, you will have no problem later when the issues of noise level, engine exhaust, radiator exhaust, fresh air intake, maintenance access route and fuel storage tank come into play.

That is usually the time when the architect and the building owner start asking whether we can exhaust the radiator hot air at the third floor level 50 meters away.

Locations of substation rooms

The actual locations of the electrical rooms at the building complex are 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 electrical rooms should be as near as possible to each other.

3) The rooms need to be accessible by maintenance vehicles and maintenance people for purposes of installation, operation and maintenance works. This should be possible without disrupting the normal operation of the building.

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) All electrical rooms should be adequately secured from possible disasters like flood, or even vandalism.

The above electrical rooms are in the category of substation rooms. For aesthetic reasons, layout of the buildings can be made such that the electrical rooms are located at a separate building adjacent or hidden behind the main buildings.

In fact, it is even preferable for the rooms to be secluded somewhere as long as all the above criteria are met because that would reduce the risks of interference to the functioning of the electrical system including accidents and even vandalism.

However, there are still a few more electrical rooms, which are needed for proper and efficient operation of an electrical installation in all buildings especially those of the multi storey and high rise types.

Other electrical rooms:

1) Electrical service ducts

Electrical service ducts or electrical riser rooms are used to house the submain cables that carry electricity supply to the upper floors of a building, which include the plants and machines at the roof top such as the chiller plants, cooling towers or the lift motor rooms.

The rising mains that supply the lateral distributions on individual floors are also located 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.

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 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.

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 electrical substation room spaces as explained earlier will then need to be provided except the authority’s electrical rooms.

The floors of this substation would then need to be specifically designed by the appointed structural consultants to handle the loads of all the substation equipment.

Electrical rooms must be planned for early in the design stage

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 and interfacing.

But that can turn to be a controversial subject so I think having a separate post on it will be better.

That is all I want to say on the electrical rooms today. I will continue again in the next post.

However, there are a few diagrams of electrical room layout that I think can help some readers make more sense of what I described above.

Diagrams of electrical rooms:

The first few diagrams show the core layout of a nurses' apartment building. The core layout means the layout of the building services infrastructure with the lift core at the center.

When the architect lays out the components of building services, this is what she need to place first.

Since this building is an eight storey building, I showed here the layouts of a few floors. This will help you see how the electrical rooms and the rooms of a few other building services go up the building floors.

I will not comment much on these diagrams today. Just observe the diagrams and you will be able to see the logic behind them.

Diagram 1 – Ground floor layout of building services



I will explain a little bit here to help the freshies get started.

ELEC – electrical riser room (I have uploaded some pictures of electrical riser rooms at this post: Electrical busduct installation pictures. Click the link and you can see what electrical rooms look like in an actual installation).

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.

Diagram 2 – First floor layout



Diagram 3 – Sixth floor layout



Diagram 4 – Layout for seventh and eighth floor



The eighth floor is the highest occupied floor inside this building. The floor above is just a roof level that is normally used to locate some mechanical services and fire fighting equipment and plants.

If there is a centralized air conditioning system in this building, then the cooling tower may also be located here.

Diagram 5 – Closer view of the electrical riser room and the Main DB



I zoom specifically to this area to show you what is supposed to be inside the electrical riser room.

Observe the legend for the upper electrical panel symbol.

The symbol legend MDB ‘7F’ stands for Main Distribution Board No 7F. “7F” means Seventh Floor.

The lower electrical panel symbol represents two electrical panels, each with labels DB ‘CR-7’ and DB ‘ECR-3’.

So there are three electrical panels inside this riser room.

I will explain why one of the DB’s is called Main DB when I touched a little on the single line diagram of the MDB in Diagram 7 below.

Diagram 6 – Layout for roof level



Diagram 7 – The single line diagram for individual apartment’s electrical panel



The main electrical supply cables to the upper floors are run inside the riser shaft.

The electrical panel for each individual nurses’ apartment is inside the apartment unit itself.

Diagram 7 above shows a typical single line diagram of the wiring for each apartment.

Now in order to get the electrical power, each of these electrical panels needs to be connected to the riser cables.

There are eight apartment units at each floor. So there would be eight sets of tap off unit attached to the riser cable inside the electrical riser shaft.

This quantity of tap off units can present many maintenance problems during operation of the building.

Moreover, the cables connected to the tap off unit also need to be protected with a circuit breaker. That means we need a panel to house the circuit breakers.

With eight units of apartment needing supply, we might as well install a large electrical panel to house all the circuit breakers to protect all the supply cables to the eight apartments.

Then we can use a busbar to supply all the eight circuit breakers.

This way only one set of tap off unit is required, which is to supply the distribution busbar inside the panel.

This is what is represented by the schematic single line diagram in Diagram 9 below.

Diagram 8 – Single line diagram of Main DB



With the entire individual apartment DB’s taking supply from this electrical panel, it is called Main DB or MDB.

Don’t let all these names confuse you. Some would call this Main DB a sub-switchboard, or a floor DB.

It is just an electrical panel upstream of the other in the hierarchy of the electric power distribution system of the building.

Okay guys. I would love to continue this further as I have not yet touch on the diagrams of the substation rooms.

It’s already 3.30 in the morning. So I will continue with this in the next post, okay.

Copyright http://electricalinstallationwiringpicture.blogspot.com Building’s electrical rooms layout

7 comments:

infallible said...

Hello Wan,

I just wanna drop by to express my deepest gratitude to u.
Thanks so much really.

I am currently an electrical engineering undergraduate who undergoes training in a consultant firm.

Ur materials presented enriches me a lot as if i am going for site inspection myself.

Thanks again..

(Haha, but some pictures are quite blur to see. Anyway, really thanks for ur precious time)

Subham said...

This blog has been very useful to me.

Do u have some original electrical layouts of residential buildings, i need them for my school project.

Thanks again, for your wonderful blog

Wan said...

Hello infallible. I will try to improve on the picture quality. thanks for dropping a note.

Subham, if you leave your email adress here. I will send a drawing or two directly.

Cheers.

(Lee Wan Seng)

Yoesia said...

Thanks a lot for giving me the idea of electricity.
it's really useful, really :)

MUHD NASEERUDDIN said...

thanks for giving such useful information

jasem33 said...

Hello Mr. wan...Your provided information helped me alot. But can you please send me these pictures including building electrical layout as well as single line diagram of MDB or to my email ; jasem33_2011@yahoo.com

UGOCHUKWU NWANETO said...

thanks dear . talk2guyucn@yahoo.com or ugoz4real@gmail.com is my mail. please send some electrical house wiring diagrams to me with their legends.