25A breaker with 12/2 NM-B

[mike93lx]

I think I know the answer already, but asking anyway.

House was built in 2003, a/c systems are all original.

I had previously noticed that my 1st and 2nd floor a/c systems (identical systems) used 10/2 nm-b and 25 a breakers. It caught my eye as it wasn't a 30a breaker but smaller is ok

In looking in my crawlspace today, I found that both lines switch to 12/2 nm-b in junction boxes. It all looks original, but i didn't check for date coding on the wire.

Is this kosher? Not sure if there is some exception for a/c compressors allowing use of 12/2.

Should I leave it alone? Swap to 20a breakers? Tear the house down and rebuild?

 

[sparky 1971]

It's fine with the 19.3 ampacity. It doesn't matter, but in 2003 it would have been fine with an ampacity of 25. I believe it was 2008 when 12/2 nm dropped to 20 amps.

 

[mike93lx]

It's fine with the 19.3 ampacity. It doesn't matter, but in 2003 it would have been fine with an ampacity of 25. I believe it was 2008 when 12/2 nm dropped to 20 amps.

Glad I asked. Thanks

 

[wyliesdiesels]

yeah its kosher. the breaker doesnt protect the wire on motor and air conditioning condenser circuits. thats the job of the overloads in the motor or motor starter

 

[alfredeneuman]

It's fine with the 19.3 ampacity. It doesn't matter, but in 2003 it would have been fine with an ampacity of 25. I believe it was 2008 when 12/2 nm dropped to 20 amps.

The rule for AC and motors has been around since the 50's (or earlier).

 

[sparky 1971]

The rule for AC and motors has been around since the 50's (or earlier).

I meant that since the house was built in 2003, the AC could have had an ampacity of 25 and still used 12/2.

 

[mike93lx]

Hits me as a little odd that they started with 10/2 and transitioned to 12/2. Almost like the electrician wanted to avoid an argument over 12/2 with the 25a breaker. Saves money and trouble over running 10/2 all the way across the house in the crawl

 

[larry4406]

Similar thread where I also had this question. One of the conclusions from the thread was that 12/2 NMB was derated from 22 to 20A when 2011 NEC came into affect.

Question for the Sparkies - Wire Size for Outdoor AC Units

Question for the resident Sparkies... I have a house where the AC unit is tripping the breaker. Oddly, last summer/fall the unit ran fine, now this cooling season breaker tripping and inoperable. Attached picture of the nameplate and breaker. The HVAC tech noticed that the breaker is 25A yet...

www.garagejournal.com

 

[Norcal]

It is code compliant for a A/C unit.

 

[alfredeneuman]

I meant that since the house was built in 2003, the AC could have had an ampacity of 25 and still used 12/2.

OK now I understand.......

 

[Norcal]

With NM cable, the 60° C rating still must be used, 20A for 12 AWG, if THHN, THWN, is/was used 12 AWG is 25Afor the A/C unit. It under no circumstances applies to normal branch circuits.

 

[mike93lx]

With NM cable, the 60° C rating still must be used, 20A for 12 AWG, if THHN, THWN, is/was used 12 AWG is 25Afor the A/C unit. It under no circumstances applies to normal branch circuits.

I'm confused now.

There is no thhn/THWN in this circuit. It's all nm-b. Are you saying that it isn't kosher now?

 

[sparky 1971]

With NM cable, the 60° C rating still must be used, 20A for 12 AWG, if THHN, THWN, is/was used 12 AWG is 25Afor the A/C unit. It under no circumstances applies to normal branch circuits.

I believe that #12 in the 60 scale was 25 back in 2003. Its was 2008 or 2011 it got dialed back to 20 amps.

I'm confused now.

There is no thhn/THWN in this circuit. It's all nm-b. Are you saying that it isn't kosher now?

It's fine now and has always been fine. The nameplate gives an ampacity of 19.3. My original post muddied the waters and I apologize. When it was new in 03, the ampacity could have stated 25 and 12/2 world have been still been ok. That wouldn't work today though.

 

[mike93lx]

All good. Interesting discussion.

 

[sparky 1971]

Hits me as a little odd that they started with 10/2 and transitioned to 12/2. Almost like the electrician wanted to avoid an argument over 12/2 with the 25a breaker. Saves money and trouble over running 10/2 all the way across the house in the crawl

The only thing that makes sense to me is if the AC was moved somewhere along the way. In 2003 the wire savings would have been peanuts vs the cost of dicking around in the crawl space setting the junction box. Now, if it was relocated and they took the existing 10/2 as far as it would go then tied in the 12/2 to complete the run, that's different.

 

[mike93lx]

The only thing that makes sense to me is if the AC was moved somewhere along the way. In 2003 the wire savings would have been peanuts vs the cost of dicking around in the crawl space setting the junction box. Now, if it was relocated and they took the existing 10/2 as far as it would go then tied in the 12/2 to complete the run, that's different.

Not the case here. The a/c's are all original and the junction boxes are about 10-15 feet away from the main, in the middle of the floor under my living room.

 

[alfredeneuman]

I believe that #12 in the 60 scale was 25 back in 2003. Its was 2008 or 2011 it got dialed back to 20 amps

2002NEC
The asterisk next to the number directs to Article 240(D)

Small Conductors. Unless specifically permitted in 240.4(E) through (G), the overcurrent protection shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG,......

It specifically permitted motors and air conditioners, not general branch circuits.

 

[sparky 1971]

Yes. I knew that but left the part out that it was for motor and ac loads only. 12/2 copper nm is and has always been allowed on a 20 amp max breaker for branch circuit wiring.