#8 on 50 amp breaker

B

bcl

Member
Location
Garden Ridge, TX
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Electrician (Owner/ Operator)
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.
 
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.
 
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.
 
Jraef said:
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.
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SER and MC cable are 75C rated and fine. It is mainly just NM that is a problem. (Maybe also UF, I forget.)
 
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
 
Jraef said:
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.
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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?
 
farmantenna said:
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
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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...
 
Mr. Serious said:
Does any manufacturer make a THHN that's not also rated THWN for wet locations?
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Actually you may want to read the products entire listing because this may be a possibility or dual rated wire. Home Depot has product listing for spool wire
 
NoahsArc said:
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...
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You have the right idea but if the owner does 🚫 t want to pay for future proofing what makes you think you have the right to spend his money that way?
 
Jpflex said:
Actually you may want to read the products entire listing because this may be a possibility or dual rated wire. Home Depot has product listing for spool wire
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No need to read beyond the labeling/identifying on the conductor itself. Unlike some items the NEC recognized conductors in article 310 are required to have all the pertinent informtion on the product.
 
NoahsArc said:
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...
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When they get that 48A rated load the 50 amp breaker is too small anyway, but it still protects the conductor.
 
petersonra said:
You have the right idea but if the owner does 🚫 t want to pay for future proofing what makes you think you have the right to spend his money that way?
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I contract ahead of time. If they think my price is excessive, then they can hire someone who'll run 8ga or whatever pinky swear amount they want.
I'm not "spending their money", they hired me to install [x] outlet size with [x] wire that I stipulated in the bid.
I don't want to get sued for someone's house burning down, what right does a homeowner have to insist I put myself into that situation to save them $50?

If it's my professional opinion (and it is) that a 50A outlet (that is in common usage often used to run 50A equipment) should be protected by a 50A circuit with 50A conductors, then that's that, they hired me in part to use that discretion.
 
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