Air Conditioner breaker(s)

[BrianJay]

The residence I am working at for a customer currently has a 60a circuit for one air conditioner and right next to it is another air conditioner with a 40 amp breaker. Both units are behind the garage. But now, They would like to have a 40 amp car charger installed.

Both A/C units are being replaced with two new units. Name plate :

Minimum circuit amperage 26.9
Maximum BKR 40 amps

The main panel is not really near by for the new car charger to run a new circuit.
So...Could I put in a sub panel, (using exiting 60 amp), with two 40 amp breakers each feeding the new a/c units. and then use the old 40 amp for the car charger ?

My only confusion is that new A/C units are very efficient and have smaller wire gauge specs than that of a regular circuit.

Summary: From the main panel a 60 amp feeding a new sub with two 40 amp, each feeding new A/C units. And old 40 amp from main feeing car charger. ?

 

[infinity]

Welcome to the Forum.

 

[wwhitney]

Yes, the minimum feeder size for a panel supplying only two A/C units, each with an MCA of 26.9, is going to be somewhat less than 2*26.9 = 53.8.

But the 60A circuit breaker for the existing unit may well be protecting conductors smaller than 60A in ampacity. You would need to check the conductor size on the existing circuit. Likewise for the circuit currently protected at 40A.

Cheers, Wayne

 

[wwhitney]

The new AC units have a running amp rating of about 20 amps each so 20+20+40 sounds no good on a 60 amp feeder if they all run simultaneously.

I believe the existing is an HVAC circuit protected at 60A and an HVAC circuit protected at 40A. The proposal is to turn that into one feeder for (2) 26.9A MCA units, and one 40A branch circuit for an EVSE.

Cheers, Wayne

 

[infinity]

I believe the existing is an HVAC circuit protected at 60A and an HVAC circuit protected at 40A. The proposal is to turn that into one feeder for (2) 26.9A MCA units, and one 40A branch circuit for an EVSE.

Cheers, Wayne

Yes I initially read it wrong so I deleted my post.

 

[Eddie702]

I don't see how. The two ACs are probably around 40 amps full load for both units. I don't know what the car charger needs but I can't see all of that on a 60

 

[wwhitney]

I don't see how. The two ACs are probably around 40 amps full load for both units. I don't know what the car charger needs but I can't see all of that on a 60

Again:

Existing

Old HVAC 1 on circuit A with 60A breaker
Old HVAC 2 on circuit B with 40A breaker

Proposed

New HVACs 1 and 2 on circuit A (sum of MCAs is 53.8A)
New EVSE on circuit B

And the proposal is fine if circuit A has an ampacity of 60A, and the EVSE is sized to the ampacity of circuit B. But as the circuits were used for HVAC, their ampacities may be less than their breaker sizes. Which would likely be a problem for circuit A.

Cheers, Wayne

 

[LarryFine]

But the 60A circuit breaker for the existing unit may well be protecting conductors smaller than 60A in ampacity. You would need to check the conductor size on the existing circuit. Likewise for the circuit currently protected at 40A.

Agreed. We need to know existing wire sizes.

 

[hbiss]

So, the question is if you have for example an AC that is labeled:

Minimum circuit amperage 26.9
Maximum BKR 40 amps

Would you be allowed to share that 40A circuit with something else? (Assuming #8 conductors.)

My opinion is no. The 40A requirement is to prevent tripping on startup or other normal conditions. If you add any other load to that 40A breaker, you no longer are providing the 40A required by the AC manufacturer.

I will even extend that situation to providing power to a service receptacle that's required next to the AC unit as is sometimes done.

-Hal

 

[wwhitney]

So, the question is if you have for example an AC that is labeled:

Minimum circuit amperage 26.9
Maximum BKR 40 amps

Would you be allowed to share that 40A circuit with something else? (Assuming #8 conductors.)

It's more of a side question that directly bearing on the OP, but sure. A couple of cases:

1) The other load is fine with the 40A OCPD. Then 430.53 would control, and I think it would allow up to a 13.1A load. (Not 100% sure on that, 430.53 is a bit lengthy).

2) The other load is going to require is own OCPD, e.g. a receptacle rated below 40A. Now you have a feeder and 430.63 applies. Again a load up to 13.1A is fine.

Both cases comply with 430.24 on the required ampacity, unless the #8s are 60C Al.

Cheers, Wayne

 

[Eddie702]

It's more of a side question that directly bearing on the OP, but sure. A couple of cases:

1) The other load is fine with the 40A OCPD. Then 430.53 would control, and I think it would allow up to a 13.1A load. (Not 100% sure on that, 430.53 is a bit lengthy).

2) The other load is going to require is own OCPD, e.g. a receptacle rated below 40A. Now you have a feeder and 430.63 applies. Again a load up to 13.1A is fine.

Both cases comply with 430.24 on the required ampacity, unless the #8s are 60C Al.

Cheers, Wayne

Agree. I misunderstood the original post. 2 new ac units on the 60 and the car charger on the 40. I was thinking the 60 and the 40...................................never mind LOL