#8 on 50 amp breaker

[bcl]

Hey all, I was recently called upon to inspect some EV charger circuits at a car dealership installed by another contractor. They used #8 THHN on 50 amp breakers for some 14-50 twist-lock receptacles. The breaker terminal rating says CU/AL 60/75. Am I reading this correctly that it is rated 60 degrees for copper and 75 for aluminum? In which case, their wire is too small. Is there some provision I'm not aware of, it would be a lot of wire they'd need to re-pull. Everything is installed in EMT.

 

[wwhitney]

Am I reading this correctly that it is rated 60 degrees for copper and 75 for aluminum?

No, that's Cu or Al, as well as 60 or 75 degrees. All four possibilities are fine.

Cheers, Wayne

 

[bcl]

No, that's Cu or Al, as well as 60 or 75 degrees. All four possibilities are fine.

Cheers, Wayne

Thanks so much!

 

[GoldDigger]

It means that as long as no other wire conditions or wire type ratings prohibit it, the 75C rating can be used.
The description on the breaker just specifies which conditions are accepted by the breaker itself.

 

[Jraef]

But it should be noted that putting #8 on a 50A breaker is only possible if this is wired using individual 75C rated conductors in conduit. So assuming that when you said "THHN", it is in fact in conduit, this is fine. If it had been run using NM cable, you are required to use the 60C rating column, in which case #8 is only good for 40A.

 

[jaggedben]

But it should be noted that putting #8 on a 50A breaker is only possible if this is wired using individual 75C rated conductors in conduit. So assuming that when you said "THHN", it is in fact in conduit, this is fine. If it had been run using NM cable, you are required to use the 60C rating column, in which case #8 is only good for 40A.

SER and MC cable are 75C rated and fine. It is mainly just NM that is a problem. (Maybe also UF, I forget.)

 

[wwhitney]

SER and MC cable are 75C rated and fine. It is mainly just NM that is a problem. (Maybe also UF, I forget.)

Yes, UF is also limited to 60C, as is LFNC/LFMC used in a wet location.

Cheers, Wayne

 

[Mr. Serious]

Note: type SE/SER was limited to 60°C in the 2014 NEC, but not in the 2017 and 2020 editions. See the discussion here:
https://forums.mikeholt.com/threads/new-heater-wiring-55amps.2576809/

 

[farmantenna]

I think the wire should be #6 because of the continuous load but I don't know the actual load. could be 30+- or 45+-. Everyone I've wired required #6

 

[Jpflex]

But it should be noted that putting #8 on a 50A breaker is only possible if this is wired using individual 75C rated conductors in conduit. So assuming that when you said "THHN", it is in fact in conduit, this is fine. If it had been run using NM cable, you are required to use the 60C rating column, in which case #8 is only good for 40A.

If this conduit were conduit underground the installation would be considered a wet location and would be a code violation to use standard THHN.

I think you’re also saying that all conductors must have an insulation rated for the lowest temperature rating for all conductors in the conduit, is this what code ask for?

 

[NoahsArc]

I think the wire should be #6 because of the continuous load but I don't know the actual load. could be 30+- or 45+-. Everyone I've wired required #6

Yes, I would personally always run #6 THHN for a 14-50R or "EV outlet", simply for futureproofing. I don't care if they pinky swear they're putting a 32A on it. Next year they'll get a new car with a 48A and won't think twice to use the same receptacle. You should size for the device as well as the wire, and if the device permits 50A size for 50, and if it's extremely common to have 48 continuous, size for 60.

That said, this is a car dealership, and we all know they're super trustworthy people whose pinky swears are worth their weight in platinum, so it's GTG...