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Re: A/C overcurrent protection #81129 07/15/02 03:25 PM
Joined: Jul 2002
Posts: 3
JERRY0129 Offline OP
Junior Member
Thanks a lot for all your input. Great BB.
I can probably get a digital image of the nameplate but I'm not sure how to attach or forward to this forum

2017 / 2014 NEC & Related Books and Study Guides
Re: A/C overcurrent protection #81130 07/15/02 03:49 PM
Joined: Feb 2002
Posts: 375
George Offline
There is a difference between what is "to code" and what is "good practice."

#12 is the MINIMUM "to code" perhaps.

This is a residence. In a residence I regard it to be "poor practice" to place a 35amp breaker on #12 wire. I would use #8 wire.

The 1999 ICC 1&2 Family Dwelling Code (4205.7) limits the overcurrent protection device of #10 wire to 30amps. This would require #8 wire. (This may be a NEC requirement also. I don't know.)

There is a reasonable rational for requiring #8 wire: When the A/C is replaced by something else not governed by the A/C exception (perhaps even a different A/C), the circuit is still NEC compliant.

Re: A/C overcurrent protection #81131 07/15/02 04:19 PM
Joined: Apr 2002
Posts: 178
Reel-Break Offline
I personally would not use the 12 because we all know the lights will dim and the home owner will be very concerned.If it`s a matter of code vs a better installation go with the 10. Remember code is the minimum..

Re: A/C overcurrent protection #81132 07/15/02 04:36 PM
Joined: Nov 2000
Posts: 2,148
resqcapt19 Offline
This is a residence. In a residence I regard it to be "poor practice" to place a 35amp breaker on #12 wire. I would use #8 wire.

Why do you say this is a "poor practice"? The breaker is only provding short circuit and ground fault protection for this circuit. The overload protection is provided by the AC unit. Under a short circuit or ground fault, there will be no difference in the trip times or the current required to open the breaker for all breaker sizes between 15 and 60 amps.
The basic NEC rules would require a #8 on a 35 amp OCPD, but motor, refirgeration and some other circuits are not required to comply wiht the basic rule. Also I don't think the #12 would increase the flicker or dimming effect on the lights. It may increase the lenght of time that they dim, but should also reduce the amount of dimming.
Dimming is caused by the voltage drop on the service conducotors. Smaller wire will limit the current and reduce the voltage drop.
Yes the code is a minimum and you can exceed the minimum. The original question asked for the mimimum conductors that are "required" for the circuit.

Re: A/C overcurrent protection #81133 07/15/02 09:22 PM
Joined: Jun 2002
Posts: 35
MikeW Offline
I also agree with what Don says and he says it a lot clearer then I ever could.

We are lucky to have such a great forum - Thanks to all!!

Re: A/C overcurrent protection #81134 07/29/02 10:36 PM
Joined: Jul 2002
Posts: 6
lynnbar Offline
Junior Member
I always use 30 amp breaker for household AC units. when i think 30 amp I think #10, like a kitchen circurt 20 amp, when i see 20 amp I think #12. and so on. depends on the lenth of run as well. 40 amp ele stove # 6.
just my 2 cents worth

Re: A/C overcurrent protection #81135 07/29/02 10:50 PM
Joined: Feb 2002
Posts: 375
George Offline
I understand the issues.

You asked about my "poor practice to use #10 wire" comment.

At some time in the future it is possible to look at the 35 (or 40)amp breaker and install some device that will draw 35 (or 40) amps.
Now we have the possibility of #10 wire carrying more than 30amp. I believe that is not to code.

I would rather avoid these types of situations.

In a non-residential setting I would have no problem using #10 wire.

Re: A/C overcurrent protection #81136 07/30/02 01:46 PM
Joined: May 2001
Posts: 36
C.Urch Offline

I believe the minimum and maximum breaker size of 35 amps is for motor start up while the full load running amps of the unit is 22 amps. The oversized breaker is so the start up current does not trip the device. # 10 wire is what I would use to feed the unit, since it would not demand more than 22 amps of continuous load during operation.

Re: A/C overcurrent protection #81137 07/30/02 05:37 PM
Joined: Oct 2000
Posts: 5,387
sparky Offline
with all due respect George,
i'm really not big on having more than one electrical code, especially if they conflict.....

nor do i wish to wire for future changes via DYI caliber hamheads who would not recognize the original circuits function/usage.....

Re: A/C overcurrent protection #81138 08/02/02 07:04 PM
Joined: Feb 2002
Posts: 375
George Offline
C.Urch ---

I believe that the code also allows the use of #8 wire in this situation. If you want to use #10 do so. If I had to hire an electrician to do this work, the spec would call for #8 wire NM-B.

sparky ---

I do very simple electrical work in residences. I try to avoid traps that "DYI caliber hamheads" might fall into. I try to be considerate to the poor HVAC man who installs a replacement for the unit.

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