Correct breaker size for an AC unit

[wwhitney]

I think Hal is correct based on 430.62.

Doesn't 430.24 apply to the feeder, since the HVAC equipment is more than a single motor, so it's either "several motors" or a "motor(s) and other load(s)"?

Also, 430.24 has to apply to a feeder that only supplies a single motor. Because one could always add a 1W token load and now you have a motor and another load. So to avoid that stupidity, it just applies to a single motor as well.

Cheers, Wayne

 

[Little Bill]

I agree I think a 30 A breaker with 10 AWG is best to be safe.

Is Ca on the 2020 code? If not, GFCI on the HVAC is not required.

 

[david luchini]

Doesn't 430.24 apply to the feeder, since the HVAC equipment is more than a single motor, so it's either "several motors" or a "motor(s) and other load(s)"?

Yes, 430.24 applies...but that is for conductor sizing.

430.62 says that for conductors sized per 430.24, the feeder OCPD shall be sized per the protective device allowed per 440.22, plus the sum of the full load currents of the other motors. Since there is only one unit on this feeder, that would be the MOCP of that unit.

So the feeder OCPD can't be larger than MOCP of the unit....

Unless the conductors are sized larger than required for 430.24, then the OCPD can be based on the ampacity of the conductors (430.62(B)). So for a 30A feeder OCPD, #10awg feeder conductors would be required.

 

[wwhitney]

Ah, I see the argument now, it's not that "normal rules apply to the feeder" it's that "motor rules are limited to the 25A MOCP," so if you exceed that then you need to use normal 240.4 OCPD sizing rules.

However, for the OP the MCA is 17.9 and the MOCP is 25A. Let's add a fictitious or future 5A non-motor load to this feeder. Then the feeder needs to have an ampacity of 22.9A, and the 430.63 would allow a 30A OCPD. #12 Cu at 75C has an ampacity of 25A, so #12 on a 30A OCPD would be OK.

Cheers, Wayne

P.S. The language of "not less than" in 430.63 seems off. 430.24 tells you the minimum ampacity for the conductors for a motor(s) and other load, but 430.63 doesn't seem to impose a maximum OCPD size for that situation.

 

[jap]

I agree I think a 30 A breaker with 10 AWG is best to be safe.

That's the most common thing to do.

No reason to reinvent the wheel here.

JAP>

 

[synchro]

I think 20 A is fine as well since the inverter compressor uses less current than its MCA rating. I just find it weird to use a 20 A breaker and a 25 A fuse.

Is Ca on the 2020 code? If not, GFCI on the HVAC is not required.

Since the OP mentioned it's an inverter type compressor, there's a risk it will cause false tripping on a GFCI breaker. From what I have seen California is on the 2017 code. And so if a GFCI breaker is not required, installing one may cause unnecessary problems.

 

[texie]

Since the OP mentioned it's an inverter type compressor, there's a risk it will cause false tripping on a GFCI breaker. From what I have seen California is on the 2017 code. And so if a GFCI breaker is not required, installing one may cause unnecessary problems.

Good points. I didn't see that he was in CA and it is an invertor condensing unit.

 

[mathcoin]

Yeah, you are right CA is on the 2017 NEC code, and I do not see any additions from CA requiring it in 210.8 and 440. CA will adopt 2020 NEC on 2022.

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I that case, should I just get a 25 amp breaker to match the 25 amp fuse? I am thinking of using 10 awg wire anyways, for an easier inspection and minimal cost.

 

[Little Bill]

Yeah, you are right CA is on the 2017 NEC code, and I do not see any additions from CA requiring it in 210.8 and 440. CA will adopt 2020 NEC on 2022.

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I that case, should I just get a 25 amp breaker to match the 25 amp fuse? I am thinking of using 10 awg wire anyways, for an easier inspection and minimal cost.

That's what I would do.