220.14 ('02nec

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brownout

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If I have a house with a 7000W electric furnace and a 6440VA air conditioner, do I add 7kVA or 8.05kVA to the demand load for the service?
 
You only need include the larger of the two as long as they cannot be run simultaneously.

Note: Beware the heatpump that keeps the compressor running during aux/emerg heating.
 
That's what I figured. So why in ANNEX D, example D1(b) did they count 125% for the window shaker (it being the largest motor in the house?)? Wouldn't a central AC condenser be the biggest motor in the house, and therefore contribute 125% FLC to the service load?
 
brownout said:
If I have a house with a 7000W electric furnace and a 6440VA air conditioner, do I add 7kVA or 8.05kVA to the demand load for the service?
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If we can assume the two won't run at the same time, Larry is right. Use the larger of the two only. The largest is the 7000 W electric furnace. But that load needs multiplied by 1.25 (because it is continuous). So you would use 8750 Watts.

Looking at the example you mentioned (I'm using the 2005 code book), they added 25% for the largest motor on each phase. They added 25% of the 12 amp condenser load on phase A, and 25% of the 8A disposal load on B. That makes sense if the largest motor is a L-N connected load on a 1 phase service, or a single phase load on a three phase service.

Steve
 
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