240V welder circuit- no neutral

[matt_i]

When I look up THHN at the places that sell it, they all rate #8 at 40A, and #6 at 55A. I'm talking individual THHN, not NM.
C.
Edit- I see what you mean. One supplier lists it at 40A @ 60C., 50A @ 75C., and 55A @ 90C. The question is whether the inspector, who only does residential will agree with that. They're used to dealing with NM.

Look here

http://www.cerrowire.com/ampacity-charts

For #6 awg, your 60deg C NM-B is 55A, THWN @ 75C is 65A and THHN at 90C is 75A.

Assuming copper of course. I have never actually seen THHN-Aluminum wire before........

 

[wyliesdiesels]

When I look up THHN at the places that sell it, they all rate #8 at 40A, and #6 at 55A. I'm talking individual THHN, not NM.
C.
Edit- I see what you mean. One supplier lists it at 40A @ 60C., 50A @ 75C., and 55A @ 90C. The question is whether the inspector, who only does residential will agree with that. They're used to dealing with NM.

It shouldnt matter if he only does residential. Table 310.15(b)(16) is at the heart of the NEC and if he doesnt understand or know the ampacity difference between NM-b and THWN, then he has no business being an electrical inspector.

I wouldnt hesistate to use THWN in a residence at its rated ampacity...

THWN can be used at 75* c ampacity. 90* column is for derating purposes only. Im not gonna go into derating as it gets more complicated and unless u have excessive heat or more than 4 CCC (current carrying conductors) in the same pipe, its not applicable...

 

[MushCreek]

OK- thanks. I'm going to go with #8. I used #6 for my range in the house, but that was NM, not THHN/THWN. Worst case scenario- He makes me put in a 40A breaker. At least I know that the circuit is safe at 50A.