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#8 THHN for NEMA 14-50 EV charging receptacle

Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Sierrasparky said:
Hi all,
Been a while since I have posted.
I have a small disagreement with a fellow contractor. The question at hand is
Is it compliant to use #8 THHN on a 50 amp breaker given the de-rating due to continuous load as we must follow her in CA?
Oh and the length of the run is under 90 feet so voltage drop should be fine.
Thanks
Click to expand...

Many chargers are running at 48 amps so 48 x 125% = 60 amps. That means you need 60 amp overcurrent protective device and 60 amp wiring. With NM cable you are restricted to the 60C column otherwise you can use 75C

If the chargers runs at 40 amps then 125% x 40 = 50 amp. You need a 50 amp overcurrent protective device and conductors.
 
T

TX+ MASTER#4544

Senior Member
Location
Texas
Occupation
electrical Code instructor and mentor
Sierrasparky said:
Hi all,
Been a while since I have posted.
I have a small disagreement with a fellow contractor. The question at hand is
Is it compliant to use #8 THHN on a 50 amp breaker given the de-rating due to continuous load as we must follow her in CA?
Oh and the length of the run is under 90 feet so voltage drop should be fine.
Thanks
Click to expand...
2023 NEC
The rules for condition of usage for T.310.16 are found in its caption and the 3 accompanying foot notes are found in that table.
Additionally, to understand how to apply those rules you must use the Code sections and related tables that are found in those foot notes.
Those footnotes and those sections/ tables refer to and support T.310.16 or vice versa.

Example: Think of the conductors for a service, a branch circuit and a feeder as kind of a loop. Those are the basic three essentials of an electrical system.

So, here are three Code sections that would apply to your question about" de-rating" and continuous loads in the 2023 NEC.

Here's the loop:
(1) Branch circuits 210.19 (A) (1) and (2)..."not less than the maximum load to be served after....."
(2) Feeders 215.2 (A) (1) and (2) "...not less than the maximum load to be served after..."
(3) Services 230.42 (A) (1) and (2) "...not less than the maximum load to be served..."
You will see that they all have the same standard that is common to them all.

Thanks for reading.
Comments accepted.
TX+MASTER #4544
 
Sierrasparky

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
infinity said:
Pretty standard stuff in commercial work.
Click to expand...
jap said:
Pipe and wire guys like me use #8 thhn on 50a circuits all day long and not give it a second thought.

JAP>
Click to expand...
infinity said:
Yes it's code compliant. I'm surprised that this other contractor is saying it's not.
Click to expand...
Yeah , got into a heated discussion with a fellow contractor the other day. He said I've been wiring these 14-50's all wrong. ( used #8) He was so adamant I thought I missed some new rule. I think because he is a rope jockey and I came from a commercial background.
 
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