[JohnsPop]

The last couple years my outside A/C unit has started tripping the breaker at random times. We often don't notice it until hot air has been blowing for a while and the house gets clammy. Most of the time I can just reset the breaker and rock on. Sometimes, it keeps tripping or it won't stay reset at all.

On the side of the A/C unit, it says recommended breaker size is 40A and maximum breaker size is 40A. Problem is, I've got a 30A breaker with 10AWG wire. I replaced the breaker last year thinking the old breaker was bad, but I replaced it with another 30A. Same situation. If I replace the 30A breaker with a 40A breaker, can I stay with the 10AWG wire, or do I need to go up to an 8AWG? The run is about 40 feet from the outside unit to the breaker box and that's the only thing on that circuit.

Yes, we will eventually replace the entire system, but you know how it is with funds and emergencies. We've made it to August again this year, so unless it goes completely out, we've scraped by for another summer. :) Thanks!

[ballengerb1]

I have deleted the chart

[ma0641]

10AWG is max at 30 Amps. 8AWG can be rated above 40 if certain wire is used. Sounds like your compressor may be going and pulling too many Amps. DO NOT put a 40 Amp breaker on the #10 as you risk causing a fire-is your house or life worth it?

[stanfortyman]

10AWG is max at 30 Amps. 8AWG can be rated above 40 if certain wire is used. Sounds like your compressor may be going and pulling too many Amps. DO NOT put a 40 Amp breaker on the #10 as you risk causing a fire-is your house or life worth it?

Sorry, this is simply not true in all cases.

A/C units follow different codes than conventional circuits.
You go by the "minimum circuit ampacity", or MCA to size your wire.
You can go as high as the "maximum fuse or circuit breaker" to size the breaker.
So... if the MCA is 30A or less, then you can use a #10 wire.
If the max breaker is 40A then you can use a 40A breaker.
Yes! You can use #10 wire on a 40A breaker.
See NEC 240.4(D) & (G)

If you up the breaker you must up the wire gauge. http://www.groverelectric.com/howto/...%20Wattage.pdf

This is an ambiguous if not flat out wrong chart. This is why I hate easy charts and tables like this. Rarely are they completely correct or give you all the info needed.

[Missouri Bound]

If you want to use a 40 amp breaker, you need to change the wiring to 8 ga. Although there are exceptions to that guideline, your equipment clearly states that you require a 40 amp circuit. The discussion over exceptions to the rule has no bearing on your situation.

[hkstroud]

The discussion over exceptions to the rule has no bearing on your situation.

What Stan quoted is the rule, not an exception.

[JohnsPop]

The minimum circuit ampacity is listed as 23A on the plate. I'm not going to "risk" anything, but I'm not going to buy additional wire if the wire I have is adequate just because I'm going to a larger breaker size. You're probably right about the compressor Ma0641, the breaker only trips in the afternoon heat when the sun is on that side of the house. It's like it only does it when the entire unit heats up and it really starts working over time. The mfg. date on the unit is 02/97 so I guess we've got the "goody" out of it. :)

Also, I'm located in Georgia if that has anything to do with any "state" codes. :)

[hkstroud]

The breaker is most likely tripping because of the high starting (temporary) amperage draw, when the compressor must restart before refrigerant pressures have equalized. This occurs during periods of high use, (heat of the day).
Your situation is the very reason NEC has special wiring rules for an air conditioner.

Increase the breaker size as specified by the manufacturer or change to a time delay 30 amp breaker.

[JohnsPop]

Awesome. Thanks for everyone's help!

[stanfortyman]

If you want to use a 40 amp breaker, you need to change the wiring to 8 ga. Although there are exceptions to that guideline, your equipment clearly states that you require a 40 amp circuit. The discussion over exceptions to the rule has no bearing on your situation.

What HK said.
It's not some vague exception to the rule, it is the rule. It is how the code reads. In this case you do not need #8 wire to use a 40A breaker.

More electricians need to familiarize themselves with 240.4(G), and not just 240.4(D).

[ma0641]

The minimum circuit ampacity is listed as 23A on the plate. I'm not going to "risk" anything, but I'm not going to buy additional wire if the wire I have is adequate just because I'm going to a larger breaker size. You're probably right about the compressor Ma0641, the breaker only trips in the afternoon heat when the sun is on that side of the house. It's like it only does it when the entire unit heats up and it really starts working over time. The mfg. date on the unit is 02/97 so I guess we've got the "goody" out of it. :)

Also, I'm located in Georgia if that has anything to do with any "state" codes. :)

Me too, Woodstock.

[JohnsPop]

I'm down in LaGrange. Well, we swapped her out today and it hasn't tripped all day. (Knock on wood) This is the time of day (6:25 PM right now) where it starts tripping. I've been feeling of the wire periodically since we swapped it and it doesn't feel warm at all. Don't know that it would, but it helps my piece of mind, anyway. :) Thanks again for everyone's help and I'll report back if anything happens. My biggest concern is that with it not tripping now, the compressor will probably go on and fail. Ah well, we'll cross that bridge when we get there.

[JohnsPop]

Just an update... the A/C has not tripped the breaker again since I upgraded to the 40A breaker. The wire feeding the unit is in a location in the basement where I walk right by it all the time and I feel it from time to time and it has never felt even warm. We had several days of 100 degrees back in August and the breaker never tripped and the unit is still plugging along. I'm putting money back to replace the unit when it finally fails, but looks like we've made it through another summer. :D Thanks for everyone's help!

[parttime]

Thanks for the update JohnsPop.