a/c install

[sminor]

installing a new a/c unit with 60A nameplate rating. using a 60 amp breaker rated at 75 degrees as the dissconnect means, with THHN type wire what is the minimum size wire that can be used? I always used #6 for this aplication, i'm told that #8 is ok. thanks for any help you can offer.

 

[Jhaney]

#8 in the 90 deg column is only rated for 55amps so I'm going to say #8 is too small

 

[sminor]

SORRY>>>I was given wrong breaker size....It is a 50 Amp used as the dissconnect means

 

[Jhaney]

#8 in the 75 deg column is rated 50 amp

 

[sminor]

I thought that the full load current of the motors caused the jump in wire size to the next higher .

 

[walkerj]

You need to know the MCA(Minimum Circuit Ampacity) and the Max OCPD for the correct wire/breaker combination

 

[Jhaney]

1. determine minimum circuit ampacity from equipment nameplate.
2. determine conductor size from table 310.16 based on step 1
3. determine circuit breaker size from equipment nameplate.

most ac units will have all but #2 listed on the nameplate

 

[Pierre C Belarge]

If the wiring method is NM cable, you will be restricted to the 60C column for your final ampacity determination.


Do not forget what Walkerj posted:
"You need to know the MCA(Minimum Circuit Ampacity) and the Max OCPD for the correct wire/breaker combination Today 01:48 PM"