i need help understanding a correction

T

Treg the electrician

Member
Location
lynnwood washington
Occupation
electrician
this i a correction i am dealing with .
we have a heat pump with a MCA 21 max OCP 25 .

I ran #12 THHN and put it on a 25 amp breaker. The following is what he stated when i questioned the correction. if im wrong could somebody please educate me here.







While Table 310.16’s ampacities are pretty much as you stated, the limitations we must comply with are the foot notes to the table identified by the asterisk (*) that appears next to the conductor sizes on the left. Here we read that #10 is to be protected at 30 amps, #12 is to be protected at 20 amps and #14 is to be protected at 15 Amps



Since your min ckt ampacity is (if I recall correctly) around 21 amps and your MOCP is 25 Amps as listed on the unit’s label you sized the OCP correctly. However, this places your #12 conductors over the 20 Amp OCP stated on the table footnote. Your will need to install #10 Cu to replace the #12.
 
The correction is incorrect.

The footnote to 310.16 says to see 240.4(D). 240.4(D) has the 20A limit for #12 conductors, however, the text at the beginning of 240.4(D) reads "Unless specifically permitted in 240.4(E) or (G), . . ." So if 240.4(G) specifically permits it, you can exceed 20A on #12 conductors. And 240.4(G) includes the reference to "Air-conditioning and refrigeration equipment circuit conductors" which need to obey Article 440, Parts III and IV. So since you have an Article 440 application, 240.4(D) does not apply to your circuit conductors.

Cheers, Wayne
 
If the #12 conductors are in a raceway they are rated in this application for 25 amps so you're code complaint. If you use NM cable then you'll need #10 AWG conductors.
 
While I agree with the other posts you might wait on input from some of our Washington members as they have their own Code which at times differs from the NEC
 
Treg the electrician said:
ok thank you for the info im going to fight it .
Click to expand...
You should. #12 THHN has an ampacity of 25 amps @ 75°C. With a MCA of 21 amps your conductors are large enough. Wayne has given you the applicable code sections which allow you to ignore exactly what the correction said that you've violated.
 
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