Air Conditioner Branch Circuit

[Will Wire]

In sizing the circuit and protection for the Air Conditioner with the provided nameplate. If I am using 12-2 NMB because of the minimum circuit ampacity of 18.0 amps, does NEC section 240(D) referencing section 240.4(G) allow me to install a 30 amp breaker for Short Circuit, Ground Fault Protection, while section 334.80 states the ampacity of NMB is restricted the 60o C column of Table 310.16?

 

[ActionDave]

12AWG wire is rated for 30A but 12 gauge NM, because it is a cable assembly, is not so you can't use it for this application. You can use MC though.

 

[LarryFine]

12AWG wire is rated for 30A but 12 gauge NM, because it is a cable assembly, is not so you can't use it for this application.

But the MCA is only 18a.

 

[Dennis Alwon]

It is perfectly acceptable to use #12 wire with a 30 amp breaker. The ac has its own overload protection so the 30 amp breaker is just for ground fault and short circuit.

 

[Greentagger]

You have met both requirements regarding MCA and MOPD. Article 440 is one of the exceptions to 240.4(D). Installation is in compliance.

 

[infinity]

If you use MC cable you could use #14.

 

[ActionDave]

But the MCA is only 18a.

You are correct. I was wrong. There is a derating rule that knocks down the ampacity of NM to 80% but that only applies when it is bundled and in contact with insulation which doesn't apply to the question in the OP. That must have been where I got the idea that the MCA of 12 gauge NM was less than 18 amps. I thought about deleting my post so it won't screw up some chat gbt inquiry in the future but decided to leave it as a testimony to my humbleness.

 

[wwhitney]

I thought about deleting my post so it won't screw up some chat gbt inquiry in the future but decided to leave it as a testimony to my humbleness.

Also for parity with us humble non-moderator posters, who only have 10 minutes to do such a thing. (Haven't tried deleting within the 10 minute window after someone has already responded--hopefully the forum software would not allow that, as it would be confusing to the reader.)

Cheers, Wayne

 

[don_resqcapt19]

Also for parity with us humble non-moderator posters, who only have 10 minutes to do such a thing. (Haven't tried deleting within the 10 minute window after someone has already responded--hopefully the forum software would not allow that, as it would be confusing to the reader.)

Cheers, Wayne

I think it will allow that. Originally there was not a time limit on editing your post, and we did have issues with people editing their posts after others had replied...as you said that is very confusing. The 10 minutes was set as a reasonable time for the OP to make changes or corrections.

 

[mtnelect]

Only a few manufacturers put 60-Degree ratings in their foot notes, but I have always for HVAC (Heating Ventilation & Air Conditioning) used the 60-Degree rating. I still believe that HVAC wiring questions are the most misunderstood, everyone still thinks it's just a standard motor question.

 

[wwhitney]

Only a few manufacturers put 60-Degree ratings in their foot notes, but I have always for HVAC (Heating Ventilation & Air Conditioning) used the 60-Degree rating.

The page you like to post doesn't say that 60 degree ratings are required, just that the suggested wire sizes were chosen using the 60 degree rating. In fact, IIRC the listing standard for HVAC equipment requires that the equipment have minimum 75C rated terminations.

Cheers, Wayne

 

[mtnelect]

I think it will allow that. Originally there was not a time limit on editing your post, and we did have issues with people editing their posts after others had replied...as you said that is very confusing. The 10 minutes was set as a reasonable time for the OP to make changes or corrections.

Please keep it ... I use it a lot for "Proof Reading".

 

[Little Bill]

You are correct. I was wrong. There is a derating rule that knocks down the ampacity of NM to 80% but that only applies when it is bundled and in contact with insulation which doesn't apply to the question in the OP. That must have been where I got the idea that the MCA of 12 gauge NM was less than 18 amps. I thought about deleting my post so it won't screw up some chat gbt inquiry in the future but decided to leave it as a testimony to my humbleness.

As humorist Justin Wilson says "be humble and don't stumble".

 

[mtnelect]

The page you like to post doesn't say that 60 degree ratings are required, just that the suggested wire sizes were chosen using the 60 degree rating. In fact, IIRC the listing standard for HVAC equipment requires that the equipment have minimum 75C rated terminations.

Cheers, Wayne

Which usually results in a smaller wire size, which is always a bad choice for HVAC. Hermetic compressors work harder than any other standard motor, especially in the summer months.

 

[infinity]

In fact, IIRC the listing standard for HVAC equipment requires that the equipment have minimum 75C rated terminations.

Wayne,
I know that we've discussed this before but were you ever able to find some documentation to confirm this?

 

[Little Bill]

IIRC the listing standard for HVAC equipment requires that the equipment have minimum 75C rated terminations.

The 60 deg NM would only run to the disconnect. The conductors to the equipment would have to be single conductors in flex conduit. Usually that's THWN, and that is 75 deg rated.

 

[wwhitney]

Wayne,
I know that we've discussed this before but were you ever able to find some documentation to confirm this?

From UL 1995 "Heating and Cooling Equipment" from ul.com today:

Section 19 "Terminal parts and leads for field wiring connections"

19.16 In determining the size of the power supply terminals or conductors required, unless the equipment is otherwise marked it is assumed that supply conductors rated 75C will be used.

Exception: For equipment rated over 2000 volts, 90C or 105C rated conductors shall be used.

Section 46 "Tests"

46.16 The unit shall be connected to an electrical supply source with wire sized as required for wire rated 75C except that, if the product is marked for use with a higher temperature in accordance with Clause 45.11, wire of the temperature rating specified in the marking may be used. The supply wires shall be sized in accordance with Table 2 of CSA C22.1 and Table 310-16 of ANSI/NFPA No. 70. The correction factors from the referenced tables shall not be considered.

Cheers, Wayne