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TDCHUNT

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How Many Single Pole 15 Amp Branch Circuits Required For A 3000 Square Foot House With A 120/240 Service. How Do You Calcuate That?
 
If that is the way a test question is worded, then the author of that question needs to go back for retraining. First of all, the NEC never requires you to install any 15 amp circuits in a residence. It does require a certain collection of 20 amp circuits, including Small Appliance circuits for the kitchen and other rooms, along with 20 amp circuits for the bathroom receptacles and for the laundry. You can install 20 amp circuits for all other lighting and receptacle loads if you like; you don’t have to use 15 amp circuits.

I think they are trying to get you to say the following:
? 3 watts per square foot times 3000 square feet equals 9000 watts.
? Subject this to a 35% demand factor, and you get 3,150 watts.
? A 15 amp circuit loaded to 80% at 120 volts gives you 1440 watts.
? 3150 divided by 1440 equals 2.18.
? The next higher number is 3 circuits.

They may vary the situation by not allowing the demand factor, in which case the answer is 7. I am sure that other members will tell you I am doing it wrong. But the truth is that it’s just a bad question.

Welcome to the forum.
 
General lighting load

3,000 sq. ft x 3 Watts per sq. ft. = 9,000 Watts

9,000 Watts / 120 Volts = 75 Amps

75 Amps / 15 = 5 - 15 amp circuits required
or

75 Amps / 20 = 3.75 or 4 - 20 Amp circuits required

or 3 - 20's and 1 - 15

or 2 - 20's and 3 - 15's

or 1- 20 and 4 - 15's


I think.:grin:
 
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