AC condenser wire size

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jgo10

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I am selling a house that was built in 1985.

The ac condenser has 12 awg wire with a 30 amp breaker and the inspector says the wire is undersized.

I believe there is an exception for Ac units because the components have overload protection that will shut the system down if it draws excess current. I am looking for a code to refer to validate this, upgrading to #10 would not be an easy task for this situation.

It is a newer unit, 17.1 is the current spec on the unit but I believe a 20 amp breaker could trip on a hot summer day.
 
Your installation sounds fine per part IV of article 440

Here is an example from Mike Holts training materials of protecting a conductor higher than article 310 tables.

Circuit Protection

Test your knowledge with this question: What size conductor and protection must you have for a 24A motor-compressor on a 240V circuit (Figure 440-6)?

  1. 10 AWG, 40A
  2. 10 AWG, 60A
  3. A or B
  4. none of these

Answer: (a) 10 AWG, 40A protection.

Here's how we arrive at that answer:

Step 1: Size the branch-circuit conductor [Table 310.16 and 440.32].

24A x 1.25 = 30A, 10 AWG, rated 30A at 60°C [110.14(C) and Table 310.16].

Step 2: Size the branch-circuit protection [240.6(A) and 440.22(A)].

24A x 1.75 = 42A, next size down protection = 40A.
If a 40A protection device is not capable of carrying the starting current, you can size the protection device up to 225 percent of the equipment load current rating (24A x 2.25 = 54A, next size down 50A).
Click to expand...

Note that in some cases the #10 could be protected at 50 A for an AC unit

Roger
 
jgo10 said:
I am selling a house that was built in 1985.

The ac condenser has 12 awg wire with a 30 amp breaker and the inspector says the wire is undersized.

I believe there is an exception for Ac units because the components have overload protection that will shut the system down if it draws excess current. I am looking for a code to refer to validate this, upgrading to #10 would not be an easy task for this situation.

It is a newer unit, 17.1 is the current spec on the unit but I believe a 20 amp breaker could trip on a hot summer day.
Click to expand...
You are correct. Tell your inspector to read 240.3, it sends you to art 440 for circuits supplying air conditioning equipment.

It isn't that a 20 amp breaker will necessarily trip on a hot summer day, it needs a 30 amp breaker is necessary so it doesn't trip on the surge current that happens during starting. If it works too hard on a hot summer day the overload protection is what would kick out.
 
jgo10 said:
I am selling a house that was built in 1985.

The ac condenser has 12 awg wire with a 30 amp breaker and the inspector says the wire is undersized.

I believe there is an exception for Ac units because the components have overload protection that will shut the system down if it draws excess current. I am looking for a code to refer to validate this, upgrading to #10 would not be an easy task for this situation.

It is a newer unit, 17.1 is the current spec on the unit but I believe a 20 amp breaker could trip on a hot summer day.
Click to expand...

The 30 amp breaker is providing short circuit and ground fault protection only and is not required to match the conductor size. The 1984 NEC would permit you to use a #14 conductor with a 30 amp OCPD for an MCA of 17.1 amps. I'm guessing that this is a home inspector?
 
Some people get confused or thrown off track by the MCA. It already has 125% of largest motor factored into it. So if you have 17.1 MCA you possibly have 12.75A compressor and 1.2 amp condenser fan.

If you ask some what size conductor is needed for two motors with that rating they will get it right but ask them what size conductor is needed for AC with MCA of 17.1 and they may try to increase that by another 125%, and if they don't wire many motors they are always confused by the allowance of higher overcurrent devices.
 
I agree with everything that was said. I am thinking that if this is in a house, it is most likely ran in romex, which would put the conductors in the 60 degree column. Which would
Make it a code violation.
 
rhovee said:
I agree with everything that was said. I am thinking that if this is in a house, it is most likely ran in romex, which would put the conductors in the 60 degree column. Which would
Make it a code violation.
Click to expand...


True but it depends on when the house was built. The OP stated that this house is from 1985, #14 AWG NM cable had an ampacity of 20 amps @60° C until it was changed to 15 amps in the 2011 NEC.
 
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infinity said:
True but it depends on when the house was built. The OP stated that this house is from 1985, NM cable #12 AWG NM cable had an ampacity of 20 amps @60° C until it was changed to 15 amps in the 2011 NEC.
Click to expand...
You sure it didn't change from 25 to 20? My 2011 says it has an ampacity of 20, but is highlighted as a change from previous edition.
 
wwhitney said:
I think infinity made a typo and was referring to #14 wire.

Cheers, Wayne
Click to expand...

Thanks for pointing that out I've made the correction. :ashamed1:

The unit referenced in the OP has an MCA of 17.1 amps so prior to the 2011 NEC you could use #14 AWG NM cable.
 
rhovee said:
I agree with everything that was said. I am thinking that if this is in a house, it is most likely ran in romex, which would put the conductors in the 60 degree column. Which would
Make it a code violation.
Click to expand...

Not always true, check out 110.14(C). Temperature rating associated with the ampacity of a conductor shall be selected so as to not exceed the lowest temperature rating of any connected termination, conductor, or device. So, if the terminals at both ends of the circuit are rated for 75 degrees you are allowed to size the cable according to the 75 degree column of 310.15(B)(16) regardless if the circuit is less than 100A.
 
ampacity of NM

ampacity of NM

jeremy.zinkofsky said:
Not always true, check out 110.14(C). Temperature rating associated with the ampacity of a conductor shall be selected so as to not exceed the lowest temperature rating of any connected termination, conductor, or device. So, if the terminals at both ends of the circuit are rated for 75 degrees you are allowed to size the cable according to the 75 degree column of 310.15(B)(16) regardless if the circuit is less than 100A.
Click to expand...

This is always confusing to me. Let us assume a new AC installation with new panel and breakers. In this case what is the ampacity of NM cable? Do we follow the 60 degree column or the 75?
 
jeremy.zinkofsky said:
Not always true, check out 110.14(C). Temperature rating associated with the ampacity of a conductor shall be selected so as to not exceed the lowest temperature rating of any connected termination, conductor, or device. So, if the terminals at both ends of the circuit are rated for 75 degrees you are allowed to size the cable according to the 75 degree column of 310.15(B)(16) regardless if the circuit is less than 100A.
Click to expand...
But if using NM cable you are still limited by the fact that you need to treat NM as 60 degree conductors. 334.80 is where this requirement is.
 
Greg1707 said:
This is always confusing to me. Let us assume a new AC installation with new panel and breakers. In this case what is the ampacity of NM cable? Do we follow the 60 degree column or the 75?
Click to expand...

You're always using the 60 degree column for type NM cable. For other types of conductors (THHN) for example, you are only limited by the lowest temperature rating of device terminals.
 
kwired said:
But if using NM cable you are still limited by the fact that you need to treat NM as 60 degree conductors. 334.80 is where this requirement is.
Click to expand...
Was it confirmed that romex was used, didn't see that. I originally pointed to 110.14(C) to avoid any confusion as to the options that are available for sizing conductors.
 
jeremy.zinkofsky said:
Was it confirmed that romex was used, didn't see that. I originally pointed to 110.14(C) to avoid any confusion as to the options that are available for sizing conductors.
Click to expand...
Actually no it wasn't confirmed, but 60C conductors still were acceptable in the OP's situation as well.
 
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