Wire size in relation to circuit breaker

I am in the process of completing the 120-hour pre-licensing course. As I go through the service and distribution panels in my home, I found that the wire sizes do not match with the amperage on the circuit breakers such as 12 AWG to 20 amp breaker and 10 AWG to 30 amp breakers. I read the previous discussions about the same topic and found out that either I will have to match the amperage from the data plate to report whether the size is correct or recommend further evaluation by a certified electrician. I have a couple of questions about this issue.

  1. Isn’t it technically exhaustive to go through each data plate to find out whether the circuit breaker is connected with the correct size of wire?

  2. If I recommend having it checked by a certified electrician, am I not taking easy way out, not doing my job properly as a home inspector?

  3. I understand that what is wrong is wrong. The undersized wire is a fire hazard. But there wasn’t any problem since they built the house back in 1992. Do I still need to mention it in the report as a safety concern or something to budget for future repair?

Thank you in advance for your thoughts.

Is it for an air conditioner condenser?

  1. No. It’s the competent way to do the job. There are not very many inductive/motor loads in the typical house that might present you with this challenge, mostly A/C condensing units. If the breakers are labeled it’s easy. If they’re unlabeled, then you can’t verify them within the scope of a home inspection so you advise that the circuits be identified, labeled and verified by a competent, licensed electrician.

  2. Yes if that becomes your default for questions that you should be able to answer. That’s what incompetent inspectors do and it’s a disservice to your client and everyone else involved in the transaction

  3. Yes. If it’s wrong, it’s wrong. Just because it did not manifest as an issue for the prior resident doesn’t mean it won’t for your client (don’t assume they will use the house the same way) and it’s likely to come up when they go to sell. Inform them so that they can make their own informed decision as to how important it is to them.

As Chuck stated in an average home there are only a few places where you would actually need to read the nameplate information. You will be inspecting that equipment anyway so it’s just something else for you to note so that you can double check the OCPD size at the panel.

Just keep in mind that the circuit breaker size and the conductor size do not always have to match. An AC unit with a nameplate MCA of 20 amps and a MaxOCPD of 35 amps can be wired with #12 conductors and a 35 amp circuit breaker.

That is where I started having questions about the wire size in relation to circuit breaker.

What other equipment or appliances in a typical house has motor? In a typical house, there is a water heater, range, dryer, wash machine, garbage disposal, and refrigerator. Here in FL, I can add a swimming pool pump and maybe well pump. Among these, I can guess the pool pump and well pump is in the same category as A/C condensing unit. Am I correct on this assumption?


I found an article that you may want to read. It is a 10 year old article but read it first - then see how some of the cited rules compare with the current NEC adopted in your area,

No for the water heater. No for the range. No for the 240V dryer. These are all primarily resistive loads.

A gas dryer, washing machine, food waste disposer, fridge, dishwasher, etc. run on standard 15 or 20A circuits, usually with plug-in receptacles.

You won’t be able to see a submersible well pump label.

About the only thing left on your list is a pool pump.

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Thank you for sharing your wisdom.

Thank you very much for the article. Now I understand how to and when to apply these rules. I really appreciate that. I can find other articles to educate myself more in that website.

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It is understandable that you are confused. Most home inspector training goes well beyond the SOP. Knowing more than is required by the SOP will help you to better understand the things that are in the SOP.

Home inspectors are not required to inspect for adequacy of design or building code compliance.

It is not necessary to try to read nameplates to determine breaker or conductor size for most circuits. The circuit breaker protects the conductors, not the load. Air conditioning units are a special case.

It is not wrong to recommend hiring an electrician for things that are outside your scope. It is wrong to recommend getting someone else to evaluate anything that is within your scope.

Thank you very much for the advise. The question originally came out of suspected wire size of A/C condenser in relation to the circuit breaker installed. I understand what your concerns are. I wasn’t trying to go beyond my scope. I was just trying to exercise what I have learned.

The A/C will have a data plate that shows the minimum circuit capacity that determines the wire size needed. The maximum overcurrent protection sizes the fuse or breaker. This is different than normal branch circuit wire sizes.

You can do that until you are crazy.