derate conductors for A/C condensor

[howardrichman]

I'm wiring two a/c condensors separately. 17.5 amps each(max brkr 25A). do I calculate the conductors rating at 120% of the load (21 amps), install #10 gu. copper on a 20 amp breaker? Could I use 12 gu. copp; or Does art. 240-4(d) referenced by art. 310-16 prohibit me from doing so. Also; would I need to use a 25 A breaker if i use 10 gu conductors even if a 20A will hold?

Thank you. HR...

 

[ActionDave]

I'm wiring two a/c condensors separately. 17.5 amps each(max brkr 25A). do I calculate the conductors rating at 120% of the load (21 amps), install #10 gu. copper on a 20 amp breaker?

The manufactures has already done the calculations for you

Could I use 12 gu. copp; or Does art. 240-4(d) referenced by art. 310-16 prohibit me from doing so. Also; would I need to use a 25 A breaker if i use 10 gu conductors even if a 20A will hold?

Thank you. HR...

240.4(D) is what allows you to use 12AWG.
The reason to use the largest breaker allowed is to take make sure the A/C unit will start every time and handle the inrush current on from the compressor.

 

[jxofaltrds]

I'm wiring two a/c condensors separately. 17.5 amps each(max brkr 25A). do I calculate the conductors rating at 120% of the load (21 amps), install #10 gu. copper on a 20 amp breaker? Could I use 12 gu. copp; or Does art. 240-4(d) referenced by art. 310-16 prohibit me from doing so. Also; would I need to use a 25 A breaker if i use 10 gu conductors even if a 20A will hold?

Thank you. HR...

Read any of 440 ?

 

[infinity]

Is 17.5 the MCA? If so you could use #14 conductors @ 75? C with a 25 amp OCPD. Also you're not required to use the maximum size OCPD. A 20 amp OCPD might work just as well.

 

[Dennis Alwon]

I'm wiring two a/c condensors separately. 17.5 amps each(max brkr 25A). do I calculate the conductors rating at 120% of the load (21 amps), install #10 gu. copper on a 20 amp breaker? Could I use 12 gu. copp; or Does art. 240-4(d) referenced by art. 310-16 prohibit me from doing so. Also; would I need to use a 25 A breaker if i use 10 gu conductors even if a 20A will hold?

Thank you. HR...

As stated a #10 conductor is not needed- 240.4(D) gives exception in 240.4(G) to a/c units. Thus you do not need to have a #12 protected at 20 amp at the panel. Remember the a/c unit has its own overload protection so the OCPD is just for ground fault or short circuit protection. The OL will had the over current and protect the conductors.

I have seen #12 wire with 35 and 40 amp OCPD and it was compliant.