New residential AC unit, old branch circuit

[fisherelectric]

New Ac has min circ ampacity of 30.4 amps. Old circuit is #8 Al SEC. If disconnect and breaker are rated @ 75 degrees can we use 75 degree column for XHHW and ampacity of 40 amps or must we use 60 degree column and ampacity of 30 amps, in which case we need a new circuit?
Inspector has already turned this down for not enough ampacity but I think he may be wrong. He also said the breaker was too big, a 40amp breaker, even though max breaker size per name plate is 50 amp max. I think he wrong.

 

[kbsparky]

I believe that the old wire is sufficient for the new equipment. Also, you should be able to utilize a 50 Amp breaker on this installation.

Is the equipment rated for use with Aluminum conductors?

Are you using the old disconnect? Copper tail into the new equipment?

 

[fisherelectric]

New disconnect, new copper to unit. Old circuit is really hard to replace. The main question here, I believe is wether or not we can use the 75 degree column or not. This inspector is definitly wrong when he says the breaker is too large for the old AC branch circuit and just doesn't know his code, I believe.

 

[Dennis Alwon]

New Ac has min circ ampacity of 30.4 amps. Old circuit is #8 Al SEC. If disconnect and breaker are rated @ 75 degrees can we use 75 degree column for XHHW and ampacity of 40 amps or must we use 60 degree column and ampacity of 30 amps, in which case we need a new circuit?
Inspector has already turned this down for not enough ampacity but I think he may be wrong. He also said the breaker was too big, a 40amp breaker, even though max breaker size per name plate is 50 amp max. I think he wrong.

The inspector is wrong. XHHW is rated 75C so you can use that column if the terminations and breakers are rated 75C. Art. 110.14 (C) may help explain this.

The OCP may also be 175% of the circuit for a/c units and can also be larger in certain situations. Art. 440.22 (A) will verify this info.

 

[fisherelectric]

Thanks...thought I was right, but nice to have you alls opinion before I dispute this inspector. The facts, sir, just the facts.

110.14(C), 110.3(B), Table 310.16, 440.22, 440.32

Steve

 

[infinity]

Since the cable is SE, all that you need is to ensure that the conductors and terminations are rated for 75 degrees as Dennis noted. SE cable is permitted at a 75 degree ampacity (unlike NM cable). The maximum OCPD can be any size between the MCA and the MOPD listed on the unit. The inspector is incorrect.