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Monday, July 4, 2016
Question:
Good morning,
We have been having a discussion about how to calculate the load and size the feeders or a service for the detached garages of an apartment complex, and are hoping you could shed some light for us on the appropriate method and if there are any demand factors that can be applied. For an example: we have 48 garages, with a ½ HP 120 volt door opener, a light with a 100 watt bulb, and a 120 volt GFCI receptacle in each garage. Do we calculate these loads as non-dwelling and use 180 VA for each receptacle, 100 VA for each light and calculate the openers as a multi motor load according to 430.24? When I do that calculation I came up with a connected load of 292 amps, are there any demand factors that can be applied to this number? Since these garages are associated with a dwelling unit, do we use 220.12 and not include the lights and receptacles since they are not included in the 3 VA per square foot calculation for dwelling units, this brings us down to 236 amps but still is quite large for what in reality is a very small actual demand. The garages would be 4 separate 12 unit buildings, one service panel and separate feeder panels at the other 3 buildings.
Thank you for all you do, Scott Halle
A
Answer:
Hey Scott thanks for your interesting question and you are welcome. Minimum lighting loads are determined, for the occupancies specified, using Table 220.12 as stated in 220.12. The lighting loads provided are not applied to spaces such as garages for dwelling as stated in the initial paragraph of 220.12. It seems surprising that 100 watt lamps would be used but if so, that is your actual lighting load. If not you can ask the AHJ if they will allow the "Warehouse (storage)" load of 1/4 VA per sq ft in Table 220.12, as that seems more reasonable.
A load of 180 VA is used for each receptacle outlet as stated 1n 220.14(I) which is not enough to apply the demand factors in 220.44. The conductor size necessary for the garage door openers is determined using 430.24. It seems very unlikely that all door openers will be used at the same time so the AHJ might allow a demand factor as stated in 430.26.