Home Electrical Question
 

I know there are a few electricians on here so I thought I'd post up:

I have a room air conditioner that pulls 12A @ 110. I ran a dedicated outlet for it using 12ga romex (just in case) and a 15A breaker that pulls off of a 30A subpanel.

For most of the day the A/C unit runs fine, but occasionally I blow the breaker and I don't know why. The unit is only supposed to pull 12A, not enough to blow the 15A breaker. I've got a 20A breaker ready to go but I don't want to put it in if it's going to be a band aid to a bigger problem.

Any ideas?

whats it draw for when it first kicks on the compressor? cuz thats gonna be the biggest draw.

12A.

Bill, you're right at the 80% rating of a 15 amp circuit. I'd step up to the 20A.

Yeah, I have been reading up on that. Looks like 20A will be the way to go.

exactly right.

the issue is probably this; when the air turns on the compressor starts, its a motor load and when motors start they draw and VERY large amount of current during the initial start-up, then settle back to the running load. This is why the 15A breaker trips sometimes. The 20A breaker will cause no issues, just dont overload the 30 sub-panel.

And like featherburner said, a circuit it not supposed to draw more that 80% of its ampacity on a continuous load, like an air conditioner. It can actually degrade the breaker and other components due to excessive heat.
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use this simple rule of thumb- if you need 12 gauge wire, you need a 20 amp breaker. if you use 14 gauge wire, use a 15 amp breaker.

True. I am aware of this. I didn't think I "needed" the 12 gauge wire, but I used it as overkill. Thanks though!

I was not aware of the fact that a 12A draw is "close enough" to a 15A breaker to trip it.

the only thing you really use a 15 amp breaker for in a house is lighting and some light duty receptacles. at least its an easy fix and you dont have to rip the wire back out. good luck

like we said, 12A will not trip a breaker, but its the starting current spike of the AC that will do it. Its probably upwards of 25 amps for a split second.
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