Hello, need to know proper load calculations for multiple unit garage/storage building.

Thanks

re: load calculations for multiple garag	wirenuts	5:10 pm saturday september 29, 2001

Table 220-3(a) lists 1/2VA per sq. ft for Garages--Commercial (storage)

re: load calculations for multiple garag	Warren Goodrich	6:42 pm saturday september 29, 2001

You need to take the square footage of the garage by the .5 volt amp per square foot as mentioned in the previous reply. Remember that if your name plate states you loads in amps to multiply by the voltage rating of that machine to get the volt amps [watt] rate. That gives you the general lighting load calculation for any general use receptacles for unknown loads in the garage considering general use receptacles, and this calculation also includes normal lighting required for the garage. Then you need to add to that answer the total of any lighting that pulls by itself 600 volt amps each. Then you need to add the following calculation. Find the largest known fastened in place motor in full loads amps found on the name plate of each motor, again don't forget to adjust from amps to volt amps by multiplying amps times voltage to get the volt amps [watts]. This largest motor includes any combination of full load currents on any one machine, but do not consider the largest horse power, only largest amps. Increase that largest full load current rating by 25% then add the full load currents of all other motors expected to be run at the same time. Don't forget to add in any autostart motors. Then add in any fixed appliance such as electric water heaters at 100%. Then add all the answers together and divide by 240 volts and this answer will be your minimum demand load of your garage service. Remember that your smallest allowable service is 30 amps if one fuse maximum disconnect, or 60 amp if 2 fuse maximum disconnect. Then the minimum size must be adjusted up for any service disconnect that has the demand load calculation answer above that 60 amps that lands between the normal fuse or breaker sizes found in 240-6 of the NEC.

Now keep in mind that we said add only the full load currents of motors expected to run at the same time. If one person max is working in the garage then you would only add the one largest motor increased by the 125%. If you have more than one person max working in that garage then you would add the next largest full load current marked on the motors for each additional person expected to work in that garage at one given time. Too that thinking you need to add the full load current of any autostarted motors such as air compressors and such.

If you have more questions add them in and we will answer what we can.

Hope this helps

Wg

re: load calculations for multiple garag	Keven	9:47 pm saturday september 29, 2001

The garage building I am trying to calculate is a 16 unit structure located on a multi-family apartment site, the plans call for building to be fed from closest house panel located on apartment building. When figuring loads do you have to allow for door openers or do those outlets fall under general use at 180va. I am wanting to run several branch circuits to building from house panel not install service at garage, need to show calculations as not to overload apartment service.

Thanks Kevin

re: load calculations for multiple garag	Warren Goodrich	11:21 pm saturday september 29, 2001

The 180 va would apply to any general use receptacle in this setting that you discribed. The motor on the door opener would be calculated as a motor or fixed appliance not as general use receptacle. Find the name plate rating of that gdo and apply that to the 1/2 va per square foot and you should have the demand load as required in this setting.

Now you do have a problem you should confirm before bidding this project. You say that you have several single circuits supplying power to that sructure that contains several different garage stalls serving each individual apartment. The only way that you can install more than one power source to that building serving as a multiunit garage would be if the AHJ agrees and rules that there is a minimum of a 1 hour fire wall separating each separate unit thus making each garage unit a single stand alone structure. This fire wall would have to reach from floor to roof deck through the attic area thus meeting the NEC requirement for these garage units to be considered separate structures allowing separate power sources. Check 210-25 and 225-30-B-1 and 230-2. I suspect you will find your AHJ will hold to 230-2 and the definition below;

Building. A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein protected by approved fire doors.

Be sure before you get too committed on this one. Check in with your AHJ or you may lose big money on this one if you don't

Let me know what you find

Good Luck

Wg

re: load calculations for multiple garag	wirenuts	7:07 am sunday september 30, 2001 1

hmmm,

well this sounds like an art 220 workout to me, with regards to 225 & 230. Can U tell us the sq. footage? Is it a detached building? Let us know and we can help crunch some #####'s

re: load calculations for multiple garag	Keven	9:46 pm sunday september 30, 2001

The garage is detached and aprox. 4000sq. ft. There is 1 keyless fixture, gfci outlet and door opener per stall ( total of 16 stalls) outside lighting consists of a total of 8 coach lights 100w max. if you have to figure door openers at name plate can you derate after certain quanity based on coincidental loads? No one stall has to be fed from certain apartment unit, plans just state from closest house panel located on apartment building

re: load calculations for multiple garag	wirenuts	5:20 pm wednesday october 3, 2001

Forgive me for not getting back to this thread,it's been balistic here. Ok some quick###'s , 4000/2+2000va...( covers your coach lights, inside lights....16 gen use receptacles =2880va.....if we say 100va for each opener , this would be 1600. Total all would be 6480va. 6480/240=27A . So if you supplied a 30A 240/120V feeder out to this, you'd be fine. And yes, this includes no load diversity as you have inquired of, but it's always good to wire for 'room to grow'