Home Electrical Question

[WildBillyT]

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?

[trashman01]

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

[WildBillyT]

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

12A.

[Featherburner]

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

[WildBillyT]

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.

[//<86TA>\\]

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


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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[nj85z28]

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.

[WildBillyT]

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.

[nj85z28]

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

[//<86TA>\\]

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


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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