A/C Condenser conductor sizing

[JohnDS]

Hey Guys. As you can see, the nameplate data says 35a max overcurrent protection.
1) Would 10awg be ok with 30a breaker or isnt a 35a breaker an odd ball?
If I should seek out a 35a breaker, should I upsize to 8awg or would 10awg still be ok?

Thanks guys, I was always told in the past to go with max oc protection when dealing with a.c. equipment, but a litte confused as I havent tackled one of these in a while. Thanks again.



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[iwire]

You can use a 25 to 35 amp breaker, I would use a 35 amp breaker with 10 AWG.

The 35 amp breaker would be a shelf stock item at the supply houses I go to assuming it is a common brand / type.

You can likely use 12 AWG with the 35 amp breaker if you wanted.

 

[texie]

Hey Guys. As you can see, the nameplate data says 35a max overcurrent protection.
1) Would 10awg be ok with 30a breaker or isnt a 35a breaker an odd ball?
If I should seek out a 35a breaker, should I upsize to 8awg or would 10awg still be ok?

Thanks guys, I was always told in the past to go with max oc protection when dealing with a.c. equipment, but a litte confused as I havent tackled one of these in a while. Thanks again.

View attachment 10436

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The conductors are sized to the Minimum Circuit Ampacity of 21 amps. This would be a #12 if using pipe and wire or #10 if using NM cable.
A 35 amp breaker is a standard size and I would use that if you can get one to avoid nuisance trips. Otherwise you are still compliant with a 30 amp breaker.
The breaker does not need to match the conductor size for this application.

 

[JohnDS]

Ok thanks....I will go with 35a ocp with 10awg.
I was about to buy 8awg for the 35a breaker. I was under the impression that for 10awg wire, the max ocp should be 30a. How is 35a ocp ok for 10awg if you dont mind me asking. I appreciate the help guys.

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[bob]

Ok thanks....I will go with 35a ocp with 10awg.
I was about to buy 8awg for the 35a breaker. I was under the impression that for 10awg wire, the max ocp should be 30a. How is 35a ocp ok for 10awg if you dont mind me asking. I appreciate the help guys.

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under normal conditions that is correct. Circuits for motors are an exception. Check this article for more information.

http://www.ecmag.com/section/codes-standards/overcurrent-protection-motor-installations-part-one

Mike Holt list of exceptions
http://www.mikeholt.com/nec-conductor-sizing-and-protection.php

 

[iwire]

I was under the impression that for 10awg wire, the max ocp should be 30a. How is 35a ocp ok for 10awg if you dont mind me asking.

In most applications we are limited by 240.4(D) to 30 amps for 10 AWG.

But there are some types of loads we can ignore that, there is a pretty long list in Table 240.4(G) Specific Conductor Applications but motors, HVAC, welders are some of them.

In your case the condenser has a built-in motor overload unit that the NEC knows will protect the conductors from overload. The breaker protected the circuit from short circuit and ground faults while the condenser motor overload unit protects the circuit conductors from overload.

Keep in mind this is only for the conductors between the condenser terminals and the first fuse or breaker. So in your case use a non-fused disconnect at the unit and run 10 AWG all the way back to the breaker in the panel.

If you put a fused disconnect at the unit the conductors from disconnect to 35 amp breaker would have to be 8 AWG.

Feel free to ask questions, that is what the forum is for. This subject is kind of complicated but knowing it can save you money.

 

[JohnDS]

Thanks guys.
Iwire, you have raised another question. In this case, Why does installing a fused disconnect as opposed to a non-fused disconnect determine that the wire from disconnect to panel be upsized to 8awg?

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[infinity]

Thanks guys.
Iwire, you have raised another question. In this case, Why does installing a fused disconnect as opposed to a non-fused disconnect determine that the wire from disconnect to panel be upsized to 8awg?

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By definition the conductors between the panel and the fused disconnect are feeder conductors. They would have different rules than the branch circuit conductors between the fused disco and the unit.

There has been some argument that the fuses could be supplemental protection and therefore the conductors would not be feeder conductors.

 

[JohnDS]

By definition the conductors between the panel and the fused disconnect are feeder conductors. They would have different rules than the branch circuit conductors between the fused disco and the unit.

There has been some argument that the fuses could be supplemental protection and therefore the conductors would not be feeder conductors.

Oh ok, understood. Thanks a lot guys for the help.

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[david luchini]

In this case, Why does installing a fused disconnect as opposed to a non-fused disconnect determine that the wire from disconnect to panel be upsized to 8awg?

By definition the conductors between the panel and the fused disconnect are feeder conductors. They would have different rules than the branch circuit conductors between the fused disco and the unit.

I believe 430.62 would allow #12 Feeder conductors from a 35A Feeder OCPD to supply the 35A Branch OCPD and #12 Branch conductors in this case. There should be no reason to upsize the feeder conductors to #8.

 

[iwire]

I believe 430.62 would allow #12 Feeder conductors from a 35A Feeder OCPD to supply the 35A Branch OCPD and #12 Branch conductors in this case. There should be no reason to upsize the feeder conductors to #8.

This is not a 430 application is it?

 

[mbrooke]

In most applications we are limited by 240.4(D) to 30 amps for 10 AWG.

But there are some types of loads we can ignore that, there is a pretty long list in Table 240.4(G) Specific Conductor Applications but motors, HVAC, welders are some of them.

In your case the condenser has a built-in motor overload unit that the NEC knows will protect the conductors from overload. The breaker protected the circuit from short circuit and ground faults while the condenser motor overload unit protects the circuit conductors from overload.

Keep in mind this is only for the conductors between the condenser terminals and the first fuse or breaker. So in your case use a non-fused disconnect at the unit and run 10 AWG all the way back to the breaker in the panel.

If you put a fused disconnect at the unit the conductors from disconnect to 35 amp breaker would have to be 8 AWG.

Feel free to ask questions, that is what the forum is for. This subject is kind of complicated but knowing it can save you money.

You rock!

 

[david luchini]

This is not a 430 application is it?

Yes, all 440 applications are also 430 applications. 440.3(A) says the the provisions of 440 are in addition to, or amendatory of the provisions of 430.

There is nothing in 440 about feeders, only branch circuits, so you have to go back to 430 for feeder requirements. And 430.62(A) specifically mentions 440.22(A) for its sizing requirements.