Residential air conditioner hook up.

[metzlers5]

I have an issue with an inspector i would like help solving. I have an a/c that has 23.2 min ckt ampacity with max breaker size of 30. What size wire can i run and what is the code article. I ran 12 ga. per art 440.6(a) and table 310.16. 12 ga thhn is good for 30 amps. For motor loads and compressors do the * apply on table 310.16?

 

[augie47]

There are many Code Articles that apply...
310.16, 240.4, 110.14, and when involved 334.80.
240.4(G) exempts you from the 20 amp limitation of 240.4(D) for #12,
110.14 prescribes the conductor ampacity based on the terminations which in the case of #12 would normally be 25 amps. (as opposed to the 30 you stated)
Your install would be Code compliant per the above articles.

 

[tryinghard]

Most likely your landing lugs are 75 degree rated if so you could use a 25A breaker, the landing lugs throughout would have to be rated 90 degrees to use a 30A breaker.

 

[Dennis Alwon]

This will be a tough effort to convince the inspector. Many EC's still don't understand why this is allow.

Your a/c has built in overload protection so the 30 amp ocpd on #12 just protects the wire from short circuits & ground faults. The wire is protected from getting too much current by the overload protect in the a/c. Good luck.

 

[kwired]

Ask the inspector what section is in violation. There are exceptions to the general rules for air conditioning, refrigeration and motor circuits.

The difference between a motor with a full load rating of 23 amps and an air conditioning unit with a minimum circuit ampacity of 23 amps is that the air conditioning equipment already has the 125% factor for continuous loading figured into that number. The actual full load current of this unit is probably around 18 amps.

 

[augie47]

Most likely your landing lugs are 75 degree rated if so you could use a 25A breaker, the landing lugs throughout would have to be rated 90 degrees to use a 30A breaker.

I don't buy that...
could be wrong, but as long as the 75? ampacity is equal or less than the 75? terminations, I think the 30 amp breaker is allowed since it's the mfg max.

 

[kwired]

conductor size and overcurrent device size are two different issues with motor loads or air conditioning and refrigeration equipment and are not at all dependent on each other.

 

[roger]

conductor size and overcurrent device size are two different issues with motor loads or air conditioning and refrigeration equipment and are not at all dependent on each other.

Meaning what?

Roger

 

[roger]

I don't buy that...
could be wrong, but as long as the 75? ampacity is equal or less than the 75? terminations, I think the 30 amp breaker is allowed since it's the mfg max.

I agree.

Roger

 

[tryinghard]

I don't buy that...
could be wrong, but as long as the 75? ampacity is equal or less than the 75? terminations, I think the 30 amp breaker is allowed since it's the mfg max.

Ya lost me #12 is rated 25A at 75??

 

[ActionDave]

Ya lost me #12 is rated 25A at 75??

Per the OP the minimum circuit amps are 23.2. 12AWG copper is rated at 25 amps in the 75 degree column, so it is all that is needed.

He is allowed to put it on a 30 amp breaker because it is the max over current on the nameplate. In this case the max over current is the same as the 90 degree scale, but that is coincidence. If the max over over current said 50 amps he could land the #12 on a fifty amp breaker.

 

[kbsparky]

Too often I have heard of inspectors enforcing 240.4(D) instead of looking at 240.4(G) in such installations.

Your inspector-critter needs to be edumacated.

A #12 conductor fed from a 30 Amp breaker would be a compliant installation in this case.

 

[tryinghard]

Per the OP the minimum circuit amps are 23.2. 12AWG copper is rated at 25 amps in the 75 degree column, so it is all that is needed.

He is allowed to put it on a 30 amp breaker because it is the max over current on the nameplate. In this case the max over current is the same as the 90 degree scale, but that is coincidence. If the max over over current said 50 amps he could land the #12 on a fifty amp breaker.

Got it :grin:

 

[russ]

While I agree with the use of the 30 amp breaker (440.22 (A) allows over current protection of 175% of the rate load). If that doesn't work you can go up to 225%.
I know a 30 is being used per manufactures instructions.
Could some one quote the section that mentions that the 20 amp limitation on # 12 can be ignored.
With the limitation in tact that would mean 16amp load x 125% = 20amp.

 

[iwire]

240.4(D) Small Conductors. Unless specifically permitted in
240.4(E) or (G), the overcurrent protection shall not exceed
that required by (D)(1) through (D)(7) after any correction
factors for ambient temperature and number of conductors
have been applied.

240.4(G) permits it.

240.4(G) Overcurrent Protection for Specific Conductor Applications.
Overcurrent protection for the specific conductors
shall be permitted to be provided as referenced in Table
240.4(G).

 

[Dennis Alwon]

While I agree with the use of the 30 amp breaker (440.22 (A) allows over current protection of 175% of the rate load). If that doesn't work you can go up to 225%.
I know a 30 is being used per manufactures instructions.
Could some one quote the section that mentions that the 20 amp limitation on # 12 can be ignored.
With the limitation in tact that would mean 16amp load x 125% = 20amp.

240.4(G), not sure what you mean by the limitation. The nameplate has 125% in it and thus the conductor must be able to carry the nameplate current. #12 is good for 25 amps based on 240.4(G) @ 75 C

 

[Dennis Alwon]

I would like to add that those of use who use NM cable know that we are limited to 60C. We are use to having table 310.16 give us #14 @ 20 amps and #12 @ 25 amps for 60C. In the 2011 NEC this is gone. #14 is now 15 amps @ 60C and #12 is 20 amps @ 60C

 

[russ]

240.4 (E) is tap conductors.
240.4 (G) is overcurrent protection.
I agree you can can use a larger than 20amp overcurrent device, I still don't see it saying you can ignore the asterisk in 310.16, that sends you to 240.4 (D) that limits the load, put on the #12 to 20amps

 

[Dennis Alwon]

240.4 (E) is tap conductors.
240.4 (G) is overcurrent protection.
I agree you can can use a larger than 20amp overcurrent device, I still don't see it saying you can ignore the asterisk in 310.16, that sends you to 240.4 (D) that limits the load, put on the #12 to 20amps

Read 240.4(D) it states unless permitted in 240.4(G) then you are limited to 20 amps OCPD

 

[iwire]

I agree you can can use a larger than 20amp overcurrent device, I still don't see it saying you can ignore the asterisk in 310.16, that sends you to 240.4 (D) that limits the load, put on the #12 to 20amps

Russ, it is right in 240.4(D) itself

'240.4(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), '