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#90577 11/30/04 07:27 PM
Joined: Jun 2004
Posts: 613
I'm trying to do a load calculation for a automotive body repair garage.What is the general lighting load(VA per Sq Ft)I should use for calculating the general lighting load?

Also should I take the largest motor in the place and multiply by 125% and add all other loads within the garage to compute the load for the garage?

The body shop has a spray booth, an air compressor with two 5 horsepower motors, and a welder.



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Joined: May 2004
Posts: 81
General fluorescent lighting systems, such as in an office building, have lighting loads of 1.5 to 2.5 watts per square foot

A fluorescent lighting system with both task and ambient lighting has a lighting load of 1.2 to 4.0 watts per square foot

An HID lighting system has a load of 1.0 to 2.0 watts per square foot.

Many booths have heat run off electric

Joined: Jul 2003
Posts: 394
Better check and see if there are any special requirements from the owner or engineer. That kind of occupancy often has special need for high intensity lighting areas. Also, will the booth be supplied as a wired unit? If so, get its exact requirements. They usually have big fans and lots of lighting.

Joined: Jun 2004
Posts: 613
This is a body shop that is open already and in need of a larger service...currently 120/240 single phase 200amp.

So...3300sq ft x 3va per ft = 9900va
Spray booth 45 amps x 240v =10800va
Air compressor with two 5 hp motors, 28amp each x 2 =56amp x 240v = 13440va
Welder nameplate = 7700va
Well water pump 7.5 amp x 240 volt= 1800va
Electric water heater 12 amp x 120v = 1440va
Office electric heat = 4000va
Spray booth lighting = 1560va
Outside HPS wall packs = 1200va
Office equipment etc. =1200va
Waste oil fired heaters =2400va
20 shop 120volt recp outlets, 20x180va=3600va
Sign circuit = 1200va

60240 divided by 240 volt =251 amps

I want to install a new service with a 400 amp panelboard with main, fed by 2 service entrance conductors 500mcm copper and a reduced neutral at 350 mcm copper in 3inch IMC to a 320 single phase meter can.I'll use pvc between the meter can and the panelboard to avoid bonding requirements.From the new panelboard I'll backfeed an exsisting 100amp sub panel and also refeed all exsisting circuits that originated from the 200amp main loadcenter from the new 400 amp panelboard.My GEC will be 1/0 copper to waterpipe with 2 supplemental ground rods.

Any input would be appreciated...


Joined: Mar 2001
Posts: 345
If you run your service entry conductors from multi barreled lugs on the load side of the meter to one two hundred ampere enclosed breaker or disconnect to feed the two hundred ampere panel and a one hundred ampere enclosed breaker or disconnect to feed the one hundred ampere panel you will save money over the high cost of a four hundred ampere main breaker panel.
Tom Horne

Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
Joined: Jun 2004
Posts: 613
Tom...thanx for the replie...with a load of 251 amps now a 200/100 amp setup as you described wouldn't leave much room for any more equipment at the shop. The owner wants 400 amps in case of future needs.Due to the location of the panels that exsist in the building,it is not feasible to install seperate disconnects.The wiring in the two exsisting panels is a mess to say the least.Guys adding and adding circuits over the years without properly figuring the load and causing a dangerous situation in my opinion.I will relocate some of the heavy loads to the new 400 amp the spray booth and the air compressor which is drawing off the 100 amp sub panel.

I did consider the type of installation you mentioned.That is what we do around here for residential 400 amp services...with dual barrel lugs and two 200 amp main breaker panels.We also feed the 320 meter with dual 4/0 URD in a 4inch PVC from the POCO manhole.



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