Breaker/Conductor Size On HVAC Equipment

SmithBuilt

I'm wiring a heat pump compressor.
Specs- 19 min circuit ampacity, 25 min, 30 max breaker sizes. All right off of the nameplate.

Using 12 ga. NM cable(existing in this case), I must use the 60C column of 310.16. Which allows 25 amps.

So can I use a 25 amp breaker on #12? By referring to 240.4(D) which sends me to 240.4(G) then to Art 400 Parts III and VI

Here's where I get confused. I cannot find where the code states that I can use the 25 ampacity figure instead of the 20 for #12 NM cited by 240.4D.

What I'm I missing?

JohnJ0906

Section 440 Air Conditioning and Refrigerating Equipment - specificaly parts III and IV - it doesnt come right out and say "you can do this " but it tells you to calculate conductors at 125% and short circuit protection at 175%. The only thing you need to see is "min circuit ampacity"-19 amps. 12 ga wire is good for 19 amps so you don't need anything else to allow you to do this.

__________________
John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC

SmithBuilt

So according to that I could use a 30 amp breaker on #12 also. Since the 175% short circuit protection would still be meet.

Or in this case since the nameplate states 30 amp breaker is ok.

RobertWilber

confusing, no?
I had problems with this for a while, but the breaker only provides short-circuit and ground fault protection. The overload protection is inherent in the AC unit
http://www.mikeholt.com/code_forum/s...earchid=182725
http://www.mikeholt.com/code_forum/s...ing+protection

Magnettica

You could use #14 AWG, and a 30 AMP double-pole circuit breaker and meet code in this situtation.

440.6
Table 310.16
240.4 (D)
240.4 (G)
110.3 (B)

But in my opinion, and if this were my job (and I have done hundreds of these split-system installs), I would use #12 AWG and use a 25 AMP double-pole overcurrent protection device.