Electrical Room Space Allocation - Grey Book? 4

[Senselessticker]

Hi folks -

I'm trying to estimate the sq. ft. (for space allocation purposes) needed for an electrical room of a commercial office building. Electrical Room will house main switchboard from incomming feed, mcc, a few low voltage transformers, possibly as ATS to emergency power, a few lighting/recpacle panels, etc... All I really know about the conceptual building is the total sq. ft. and number of floors.


I suppose my chain of thought is this:

A) Determine total motor, recptacle, and lighting loads.

B) Use this information to determine size/kind/quantity of equipment needed in electrical room(s).

C) Use this information to return final result of sq. ft. needed for electrical room allocation.

Now I have two questions:

1) Am I taking the right approach to the problem (sq. ft. needed for electrical room allocation including smaller rooms throughout the building)?

2) Is the Grey Book my best source of information to estimate quanity and type of loads within the building?

Many thanks for any response!

Sense

 

[BJC]

I would start with 10 va per square foot.
That will give your a good enough number for a start. After you get the size of the service you need get vendors to submit some prelimimary drawings for switchboards. The NEC (section 110) has clearance requirements as well as what you need for exits. I usually make scale cutouts of the gear and the required clearances and play "paper dolls" to make things fit.
In the preliminary stages be generous. When you give your requriments to the architech they usually want to cut it in half.
If the building has a server room in it The load can be anyting from 50 to 100 Va per square ft (plus a cooling load ). Server load and the knowledge about them seems to be changing every week. I would google up things like "electrical requirements server rooms".

 

[Ashereng]

Also remember to allow room to manuever your equipment. Leave sufficient access way, isle way, door/panel opening, turning radius, etc.

 

[davidbeach]

Design around the physically largest gear that might possibly be acceptable on the job. DO NOT design for the most compact installation. If you can, design using "paper dolls" that are 15-25% larger than anticipated. By the time the project is finished there will always be more stuff in the room than was planned for when the size was finalized.

 

[alehman]

The size of equipment varies significantly between vendors. Be sure to consult with each vendor listed as acceptable in your specifications. Also, be sure the vendors have your specification to size the equipment, since some spec items can drastically affect the size. Consider planning space for future expansion.

 

[advidana]

What I use to size an electrical room on the 1st floor of a simple commerical bldg.

First determine the size of a simple office bldg or store bldg. For example: on bldgs under 2500 sq ft with heat pumps without strip heaters and the bldg has no elevators or electric ovens. Allow about 200 amps, 3 phase, 120/208 vac for every 400 sq ft. Also Provide load amperes for signage and plylon sign and parking lot poles lights and bldg lighting wall packs.

Once the total size of the service is known then allow 4 sq ft for each service pull section, each main section and each meter section. Allow 3 ft clearance in front on every section. If service is 1000 amps or larger then allow 6 ft in front of every section. allow a two a ft adjacent to each side of service switch gear line up for mounting house electrical panelboard, fire alarm and security panels and telephone board on oppposite and adjacent walls. If the the bldg has a fire sprinkler riser room provide space and power for the fire sprinkler alarm panel.

A typical room could be start at 20' by 10' on grow larger by service size. Put your entrance door on the exterior wall of the bldg and have the switchgear sections on the opposite walls from the exterior electrical room door. have them provide 6 ft opening to the electrical room so you can get you equipment in the room. The walls should be fire rated one hour walls or more- check your local bldg code on this.

There is a lot of other ways of doing it but this example should get you started and put you the ball park. You still need to follow NEC loads calcs and NEC spacing requirements and actual mfg sizes of equipment for the finished design which may change your room size.

Alway look out for surprise large loads the client manages to include at the last minute, like a adding strip heaters to the heat pumps or proving a vac pump for a dry fire sprinkler systems or adding elevators or any large motor etc.

Once you have done a few dozen of all types of these bldgs It get's easy to figure out. The best least costly way is to mount all the equipment outside of the bldg if the client will let you.