Wire size for 40A welder

[someone]

To connect a welder about 15 feet from breaker box. The welder says primary amps 40. A wire chart on a website shows #6 as 37.5 amps. Will #6 be close enough or should I use #4? I know the welder will not be drawing full amperage most of the time, only on spikes.

Thanks

[Steve Barker LT]

Be advised, the welder will NEVER pull what it says it will. They are highly overrated. Besides a #8 would be fine for 40A. 10ga on a 30a breaker will work fine.

Steve Barker

[RBM]

If the welder actually draws 40 amps, #6 copper would be fine

[Steve B]

Consider what would happen if you put in too small wire. You get to do it again, and pay more.

Do it once. Do it right.

What if you decide to get a little bit bigger welder? Or if you like welding, and use it enough to really heat up the wiring?

Copper is expensive now, but nowhere near the cost of doing it twice.

Steve

[Doug Miller]

Wow, I wonder where they came up with that. The National Electrical Code shows #6 copper at 55 amps.

Neither -- #8 copper is quite sufficient for 40 amps. If you're using aluminum, then you need #6. But in no case do you need #4 for a load of only

40 amps.

[someone]

Here's the site: I thought it shoul be higher than that....

seems to me like the old cable type service entrances for 60A service were #6-3 plus ground (wrapped around the bundle).

Thanks

[James "Cubby" Culbertson]

I'm no electrician so I'm not sure what they're giving the specs for but just think of it this way. According to that table, 14 ga is only rated to

5.87A. We all have a lot of problems if that's the case given the number of 15A circuits we have in our houses! I'd look for another chart or better yet, get into an NEC manual. If memory serves, 8 ga THHN/THHW or NM should work fine for 40A. Cheers. cc

[Doug Miller]

Below the table, it does say "The National Electrical Code [NEC] requires their own cable sizing for premises wiring. Refer to the NEC rules to determine building wiring, as this page relates to electronic equipment wiring."

This is then followed by a sample list of wire guages and supposedly NEC-permissible ampacities, which I will *not* reproduce here because it's wrong.

Sounds about right.

Good luck, and stay safe.

[someone]

I looked at that chart again, and it really is screwy. I was too quick to find a chart and did not spend much time reading all of it. So much for that POS chart.....

Thanks