A/C breaker too big?

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Old 02-21-08, 05:27 AM
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A/C breaker too big?

I'm buying a new house, and during the inspection the inspector noticed that the breaker for the A/C unit was too big. It's a 50 amp, and he said it should be 40 amps. The sellers called the company that installed it to have them look at it. They said they do that on purpose for the days in the summer when the unit might be working really hard. That way the breaker won't trip.

I guess that makes sense to me, but is that safe? I don't know what the wiring size is, but the inspector commented on another 50 amp breaker that didn't have the proper size wiring, so I'm guessing that the breaker for the A/C has proper wiring.
 
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Old 02-21-08, 06:09 AM
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check the namplate of the unit

Look for "Max circuit breaker size", or similar verbage. The summertime story is not a good one.
 
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Old 02-21-08, 06:16 AM
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The unit will have a data plate on it. Look where it says circuit size and breaker or fuse size. Wire sizing for AC unit is different than other circuits.

If it says fuse there must be a fuse somewhere in the circuit, most commonly at the disconnect near the unit.
 
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Old 02-21-08, 08:50 AM
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Originally Posted by Crocostimpy View Post
the inspector commented on another 50 amp breaker that didn't have the proper size wiring, so I'm guessing that the breaker for the A/C has proper wiring.
When powering a motor load (like an air conditioner or workshop air compressor), the breaker does not always have to match the wiring size. It's highly dependent on the situation.

The critical things you should look for on the air conditioner specifications are the "min circuit ampacity" rating and the "max overcurrent protection (OCPD)" or "max fuse" rating. This information should be stamped into a metal plate on the outdoor A/C unit.

The wires should be no smaller than the min circuit ampacity rating, and the breaker should be no larger than the max OCPD or max fuse.
 
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Old 02-21-08, 11:00 AM
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I talked to the inspector about this again. He told me that the maximum breaker size recommended by the manufacturer is specified to protect the unit from damage due to too much current. I wasn't thinking about it that way. I was just thinking about keeping the breaker from tripping under a heavier load on the unit. I didn't think of possible damage to the unit. After realizing that, I decided to request that the installers change the breaker to the specified size.

We'll see how that goes. ; )
 
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Old 02-21-08, 12:32 PM
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Just chiming in my agreement with the others
 
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Old 02-21-08, 12:59 PM
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Also be advised that the disconnect near the unit generally is just a service switch, not over current protection. Many a/c units have their own overload protection inside so the breaker never sees it. This is the reason its ok to see #10 wire on a 40 amp breaker on motor ckts. No worries. Like everybody is telling you though, read the nameplate! Good luck! My 2 cents.....
 
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Old 02-21-08, 04:31 PM
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Originally Posted by Crocostimpy View Post
I talked to the inspector about this again. He told me that the maximum breaker size recommended by the manufacturer is specified to protect the unit from damage due to too much current....
I was taught the breaker was to protect the wiring not the device. Lots of devices you use would fry long before a 20a breaker would trip baring a direct short. But then I guess motors are a special exception.
 
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Old 02-21-08, 04:59 PM
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Breaker rating takes into account the current inrush when the motor starts up. Doesn't let it go too far beyond that. The wiring should always be overrated. That's why there's a minimum gauge for the wiring, instead of a maximum.

"The wiring needs to be tougher than the load"
 
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Old 02-21-08, 07:14 PM
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I only have a 15a, 240v circuit for my A/C.
 
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Old 02-22-08, 11:45 AM
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Originally Posted by OregonYeti View Post
The wiring should always be overrated. That's why there's a minimum gauge for the wiring, instead of a maximum.
Really? "Always"? That sounds like a wasteful philosophy. What if the unit is only 15' from the panel?


The breaker protects the wire, NOT the unit. PERIOD.

A/C units have different rules than other loads.
As others have said, there is a minimum circuit ampacity on these units. The wire gets sized to this.
There is also a maximum OCPD (breaker or fuse). THIS is your maximum breaker size, REGARDLESS of wire size.
 
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Old 02-22-08, 11:59 AM
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By overrated, I don't mean above code requirements. I mean that code requires wire be thicker than what's absolutely necessary.

Let's say you replace an old condenser unit with a new one that specifies lower-rated breaker protection . . . would you leave the old breaker in there? I wouldn't.

I should add that I'm not an electrician and, at least here in Oregon, that wouldn't be part of my job.
 
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