I am looking to install a subpanel in my shed. I know I have the ampearge at the main. I plan on running a welder (rated at 70 Amps), some power tools (table saws, chop saws, etc.) a small portable air conditioner, and some lighting. I don't plan on using the welder a lot, but want it available. I am using 1-1/2" gray plastic conduit. Not sure whether to go copper or aluminum. Do you think the aluminum will heat up too quickly? Am thinking MHF 2-2-4-6 with a 100 Amp breaker at the main, 60 for the welder and a couple of 20's for the other tools. Do you think this will be adequate? Thanks in advance!!

 

Aluminum cable is the industry standard for building feeders. Temperature is already figured into the amperage ratings. If you do go with the #2 you'll need to breaker it at 90A; but that will still be plenty enough for what you plan to run.

It'll probably be easier to pull individual conductors (such as XHHW) through that conduit, but the MHF would be OK if you don't have too many bends.

 

Ben, Thanks for the information! It is greatly appreciated. One thing I forgot to mention, the run is about 110 feet between main and subpanel. Will this distance affect the wire size?

 

That distance shouldn't be a problem. Do you know the duty cycle on the welder or have a model number?

 

Welder is a Miller Thunderbolt XL. Rated weld output AC/DC, Volts - 30/25, Amps 300/200, Duty Cycle 20%, Max OCV 80. Input - 220V, 70 Amps.

 

That should be no problem. The welder circuit should be installed from the subpanel to the welder with #8 copper and a 90A breaker (note these breaker and wire sizes only apply to this welder).

 

 

Also, can the XHHW be run all the way from the main to the subpanel inside the gray pvc conduit, or will I have to transition wire and/or conduit at the service body once I penetrate the interior of the shed? If I use the gray conduit from exterior service body, the radius of the elbow is too wide. Should I then use a service body on the interior as well to get me to the subpanel. I was thinking maybe a white PVC elbow would get me the tight radius I need.
Thanks again!!

 

Plumbing parts are not allowed to be used with conduit.

You could use:

 

XHHW can be run from panel to panel as long as it is in conduit the whole run, be it inside or outside.

 

No problem with it. The larger breaker is to accommodate the quick surge that happens when you first strike the arc. During normal welding at 20% duty cycle the breakers and wiring have plenty of time to cool down between surges. The code book has a table with a rating factor that I used to make the breaker and wire calculation.