Friday, April 22, 2011

Electrical riser rooms

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

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

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

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

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

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

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

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

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

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

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

Larger cables cost more money.

Diagram 3 – A ground floor layout of building services

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

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

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

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

ELEC – electrical riser room.

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

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

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

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

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

TEL – for telephone cables and equipment.

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

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

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

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

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

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

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

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

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

Individual floor electrical rooms

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

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

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

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

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

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

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