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Queens, NY
reply to nunya

Re: A/C breaker issue

said by Bruschi:

So the max continuous watts would be around 1440 for a 15 amp breaker?

said by nunya:


Not exactly (and nunya knows this).

The max continuous volt-amps for a 15 amp breaker is 1440 volt-amps (VA). The continuous wattage for the breaker depends on the power-factor of the load. Since generally, few know what the power factor of their loads are; this makes it very difficult to add up the total wattage to determine if your breaker is going to be overloaded. This especially for people without much electrical experience. Its often easier to simply use 'watts' instead of volt-amps; but when the results are within - plus or minus - a hair of tripping the breaker, its better to use accurate math.

Its much more easier to understand Amps. The max continuous amps for a 15A breaker is: 15A * 80% = 12A. After the 9.2 amps of your air-conditioner, you have 2.8 amps left to spare for continuous loads. If you were to subtract the 1020W of your AC unit from 1440W, you would get 420W. And it would be wrong. You might think you have 3.5A to spare. You don't. The advantage you have here, is that the from the ratings you have on your AC unit, you can calculate its rated volt-amps (VA) and even rated power factor (p.f.):

9.2A x 120V = 1104 VA
1020W / 1104VA = 0.92 p.f. or 92%

On the other hand, nunya's assessment of the reason your breaker is tripping is spot on. You have an overloaded circuit. Very often homeowners believe they know exactly what is on the breaker; but forget or don't realize there are other loads on it. Its wise to shed some loads from this circuit to the point at which the breaker does not trip (or even provide a dedicated circuit for your air-conditioner). Its even more important in this heat, as your wiring at some points is likely exposed to outdoor temperatures. Their capacity is reduced with increased ambient temperatures.

(FYI - in NYC, homes without central AC require dedicated air-conditioner receptacles & circuits in all bedrooms, the living room & dining room).

said by mackey:

Lol wut? I've never seen a window unit on a 30A breaker.

Then you haven't been around. I have a window unit that has requires a 30A circuit & receptacle. And its 240V.... Yes, its a window unit. That being said is probably one of the largest ever made. And it is older and less efficient. 40k BTU per hour. Yes. Its a window unit! (My problem is it fits in only two windows in the house.)


I was in a newly-renovated Residence Inn in Montreal in 1997. Our room had a standard window air-conditioner and a fuse box! The air-conditioner kept blowing the fuse, the so maintenance man replaced the 15A fuse with a 20A fuse. And he gave us some 25A fuses to use if the 20A fuse blew!

Somehow, the hotel didn't burn down.

This hotel also didn't have pressure-balanced controls in the shower, so you got scalded whenever someone flushed the toilet.

Don't know how the place ever passed inspection. (I guess I do know - Google: Quebec construction corruption.)