One that the traditional things house inspectors look in ~ while inspecting an electric panel is comparing wire sizes come circuit breakers sizes. As soon as a cable is too little for a circuit breaker, you have actually a potential fire hazard. Circuit breakers safeguard the wires from overheating. While the true formula for figuring out precisely how much current a cable can lug is relatively complicated, most home inspectors rely on a simplified version the this because that branch circuits:

Breaker or Fuse (amps)Min. Copper wire dimension (AWG)
1514
2012
3010
408
556
704

For the complete story, you’d need to start v table 310.15(B) (16) in the National electrical Code, but there are a ton the exceptions that make it challenging to completely figure the end the exact answer. Thankfully, this streamlined chart works for most of the stuff ns come across as a house inspector. Wires deserve to be larger, however not smaller sized than this… for the many part.

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One such place where these rules because that circuit breakers or fuses don’t apply is because that air conditioners and heat pump circuits.

Note: while ns say circuit breaker throughout this post, what ns really average is the overcurrent defense device, or OCPD. An OCPD is a share tongue-twister because that a circuit breaker or fuse.

Minimum Circuit Ampacity

For air conditioners and also heat pumps, the only thing we should look in ~ is what’s published on the compressor unit. These devices all have a label used to them that tells united state the minimum circuit ampacity, and the preferably fuse or circuit breaker size.

The minimum circuit ampacity tells united state how huge the wire needs to be. I usage the streamlined chart over to aid determine this. If the minimum circuit ampacity claims 14.9 amps, we’re great with 14-gauge copper wire. If it states 15.1 amps, we must step it up to 12-gauge copper wire. If it claims 34 amps, prefer in the instance below, we require 8-gauge wire.

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Again, in the situation of air conditioners, us don’t require to match up the dimension of the circuit breaker to the cable sizes. To paraphrase indigenous EIOED, this is since air conditioner compressors contain heat cutouts draft to help prevent damage to the units, and also these would certainly open before it came to be a trouble for the wires.

The minimum circuit ampacity also tells united state the minimum size of the circuit breaker; it requirements to be sized big enough to assist prevent nuisance tripping when the wait conditioner very first turns on.

Circuit Breaker Size

To recognize the best circuit breaker dimension for an waiting conditioner, we look in ~ both the minimum and maximum dimension allowable. The maximum size will be clearly labeled ~ above the compressor label. In the example below, it’s 60 amps.

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What’s unusual around this number on wait conditioner data plates is that it often doesn’t jive v the chart I listed above. I mentioned that the minimum wire size for this waiting conditioner would have to be 8-gauge, and a 60-amp circuit breaker would typically be too huge for that dimension wire… however it doesn’t matter. It’s ok for this to happen here.

The circuit breaker also needs come be large enough to support the minimum circuit ampacity, which for this instance would it is in a circuit breaker rated because that at least 34 amps, which method we’d jump up to a 40-amp circuit breaker.

The most typical defect the we uncover is an overlapping circuit breaker. Thich commonly happens since an wait conditioner is replaced with a more efficient unit, however the circuit breaker in the panel is not changed with a smaller sized one. If the electric disconnect at the exterior has actually fuses that are sized appropriately, however, then it would certainly be acceptable to have a circuit breaker the is oversized.

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Summary

For wait conditioners and heat pumps, we size the wires and circuit breakers in accordance v the information printed ~ above the label, no the streamlined sizing charts that we commonly rely on.