Air Condition and Heat Pump over current protection and wire sizes. Chelan County Real Estate Inspections
I see a lot of heat pumps and air conditioning unit. These are some of the more expensive components of a home. So when performing home inspections this is an item I look over well along with the associated disconnect.
I will usually remove the disconnect cover and plate to evaluate the fuses and wiring associated with them. But one thing as a home inspector you have to be careful of is proper evaluation of the wire size. (I have been guilty of this on a home inspection).
It is not uncommon to see wire sizes that may be much smaller than normal for a specific breaker or fuse.
For instance you could 10 gauge wire protected by a 50 amp breaker and it would be correct… for that specific AC unit.
The most important thing is to look at the manufacturers label/name plate. This will give you the information you need to make a quick evaluation in the field.
Here is an example from a recent home inspection-
You can see that this name plate states a minimum circuit ampacity of 20 amps. This tells us what minimum wire gauge we need, which is #12 wire.
The maximum fuse or breaker is 35 amps. So for this piece of equipment we could have 12 gauge wires being protected by 35 amp breaker and it is correct. Really it is that simple.
If you want to be have fun with some math this is how you come up with the calculations yourself.
The air conditioning unit has a 15.3 RLA (rated-load current). For Air-Conditioning and Refrigerating Equipment we can run this at 125 percent of the normal load rating for the conductors per NEC 440.32. This is 19.125 amps and then we add .9 FLA (fan load amps) we come to 20.025 amps, round down to 20 amps. This shows us we can use #12 wire.
For the breaker we use the same information (15.3) but we now multiple by 225 percent per NEC 440.22 and we get 34.425 amps plus the .9 FLA and we get 35.325 amps, round down to 35 amps and that is our maximum breaker or fuse size.
This little knowledge will help you make your evaluation more accurate.
“If you think it's expensive to hire a professional to do the job, wait until you hire an amateur.”
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