Slightly OT: mig welder


Old 11-27-06, 10:07 PM
Thread Starter
Join Date: Sep 2004
Location: Saint Louis
Posts: 259
Slightly OT: mig welder

I'm looking to build a small workshop outbuilding. I practically stole some copper #6 THWN from Lowes, strangely the Home Depot guy said they won't resell returned cut wire b/c of the liability.

So it looks like I can do 60, maybe 70 amp to the building.

My question is, if I'm doing 220, would 70 amp be enough to do some MIG welding? I don't know anything about welding other than MIG is good for beginners.

If it matters, I'm planning on using sched 80 pvc 18" deep and using a 100amp panel in the shop.

Thanks, sorry so offtopic, but this is my favorite of the diy forums.
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Old 11-28-06, 07:28 AM
Join Date: Aug 2004
Location: NA
Posts: 1,065
First you have a lot to think about as far as the proper means to get power to the sub-panel. Best to run a 4 wire feeder (H-H-N-Grd). #6 copper thwn in conduit with 75C rated panels at each end of the feeder will let you have an ampacity of 65 amps. Your breaker in the house service panel can be 70 amps.
Your grd will need to be #8 copper minimum unless you use a 60 amp breaker then you can go with a #10 ground.
65 or 60 amps will be fine to do any mig welder that is 120 or 240 volt for residential applications and have some receptacles for tools and even an air compressor and of course lights.
You dont need sch. 80 underground ...sch. 40 is fine. Use 80 above ground where subject to damage though. Sch. 80 is hard to find at the box stores.

Be sure to ask here at this forum all the methods of wiring you need to be familiar with as to grounding and bonding at the sub. And it would be a good idea to run down to Lowes Or HD and find one of their DIY books that has a sub-panel install described so you can be up on what is required for a detached building.

You need to have a disconnect at the shed/workshop. There are a lot of ways to do this....main breaker in the 100 amp panel or an mlo panel and a seperate disconnect located on the outside of the shed (rainproof) or hit the disconnect inside as soon as the feeder enters the workshop then on to the mlo panel. An mlo has lugs only and no main breaker. I prefer a disconnect and mlo panel. Sometimes the cost savings when buying a economy package 100 amp main breaker panel is hard to beat and will give you the disconnect requirement. Some may argue the 6 disconnect rule but I'm not in favor of that arguement.


Last edited by Roger; 11-28-06 at 08:42 AM.

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