Help Sizing for an A/C Condensing Unit

[DJFNEC2005]

Hi,
I am trying to recall the correct sizing requirements for the equipment conductors, Disconnect and HACR breaker on an outdoor A/C Unit. It's been a while since I have needed to calculate these.

The nameplate on the unit states:

208/230v 1 phase
Compressor RLA = 20.0
Compressor LRA = 150

Minimum Circuit Amps = 32.5
Maximum Fuse Amps = 50
Maximum Breaker Amps = 50

I must use the nameplate ratings for sizing if present based on article 440.

I also recall being allowed to use the 75 degree column of Table 310.16 for circuits below 100 amps provided all terminals of the circuit are rated at 75 degrees. Otherwise the 60 degree column would be used.

With terminals all rated at 75 degrees, I would need a minimum conductor size of #10 THHN given a minimum circuit amprage of 32.5. #10 THHN is good for 35 amps based on tables 310.16, 240.4(D) & 240.4 (G).

This would allow a minimum non fused disconnect rating of 30 amps and a HACR breaker of 50 amps based on maximum breaker size on nameplate to be used.

Am I correct in each part of my sizing calculations?
Thanks

 

[Minuteman]

You are correct if you are using THHN/THWN. If you are using Romex, you need to use the 60 degree column and that would require a #8.

 

[stickboy1375]

Yes, #10 THHN, backed by a 50 amp HACR breaker would be fine.

 

[Minuteman]

This would allow a minimum non fused disconnect rating of 30 amps and a HACR breaker of 50 amps based on maximum breaker size on nameplate to be used.

Don't use a 30-amp disco on your Max 50-amp circuit. FWIW, the non fused discos that I buy have the same price for a 30-amp as for a 60-amp. So, I stock only 60's. :smile:

 

[DJFNEC2005]

Thanks..I will be using MC Cable switched to THHN in EMT down the interior wall and poke through to the disconnect. I am aware of the 60 degree rating of romex cable.

For what it's worth I will most likely use #8 THHN with a 60 amp disconnect anyway just because the minimum amps are close to maxing out the #10 THHN. You know how these units run a few years down the road when they are dirty and the freon charge gets low. The amprage starts to creep up fast. Even with the 125% ampacity calculated into the min circuit amps I would rather be safe than sorry.

Thanks again for the fast responses!