8awg XHHW AL on a 37A AC condenser load?

[Mgarf33]

I have a situation where an AC unit is being upgraded. The existing circuit is 8awg XHHW AL, approximately 85’ located mainly inside a conditioned space between floors & walls, not in attic or crawl space.

I know article 440 allows the minimum circuit amp rating of the equipment to determine the conductor size. The MCA rating of the unit is 37A, but the MOCP is 60A.

The existing breaker size is 30A. Article 310.15 states XHHW is rated for 75°C /40A installed upto 100’ in an 86° temp location. Obviously all lugs must be rated at 75°C or higher.

I’m not so comfortable throwing in a 60A breaker on this circuit. I’m thinking a 40A breaker, and install a hard start kit on the equipment to help reduce inrush current time.
Any thoughts???

 

[Mgarf33]

Nominal current on this 2 stage unit will likely be =/<20A, total RLA/FLA 30.1A on high stage.
LRA 152.9 on compressor.

 

[infinity]

For me a 60 amp OCPD and the #8 Al conductors. Nothing wrong with that.

 

[Mgarf33]

For me a 60 amp OCPD and the #8 Al conductors. Nothing wrong with that.

Ok, thank you, I appreciate your wisdom.
While I do have my electrical education, and have experience in rebuilding generators. I am mainly HVAC, so I don’t run wires on a daily basis. I don’t like to short cut anything especially conductors, that’s why I like asking for help here.

 

[infinity]

Ok, thank you, I appreciate your wisdom.
While I do have my electrical education, and have experience in rebuilding generators. I am mainly HVAC, so I don’t run wires on a daily basis. I don’t like to short cut anything especially conductors, that’s why I like asking for help here.

Here's a little expansion on what you have, the unit has an MCA of 37 amps which means that the running current is closer to 30 amps. Your conductor is rated for 40 amps so there should never be a problem with those conductors heating up.

 

[Mgarf33]

I believe my initial measurements were correct. Outer diameter of 6awg AL 7 strand conductors in a XHHW cable set are .28". From what I was reading the outer diameter of 8awg is .25" or 1/4" vs. 9/32". It's hard to tell the difference in 1/32". I did use a micrometer and measured between .28-.30"

What I thought was 8 is actually 6. I had to explode a picture of the label on the side of the wire.

So, now my question is, why are they installing 50A wire on a 30A breaker/circuit?

I did find another part of the NEC which would reduce the rating of 75°C XHHW to 60°C if it runs through insulation, which it may do for several feet.

In any case 40A @ 60°C for 6awg XHHW is still above the 37 MCA which is the proper conductor size for the equipment.