I'm doing some electrical upgrades to my garage/workshop with upstairs apartment; I'm going to be replacing its 1960s-vintage subpanel which is fed by #4 wire from a 200 amp service entrance panel (on the house, about a 40 foot wire run).
While out shopping for a bench grinder (1970s Craftsman; I'll take 50 years old, a little rust, but Made in USA over brand-new cheap Chinese crap any day) I found that the seller had an old Miller welding machine which he was willing to let go for a reasonable price. It looks to be in decent condition but the power cord is deteriorated and will have to be replaced prior to use. I'll need to install a suitable outlet for it…nameplate specs are 230 volt, single phase, 37 amps. The plug currently on the machine is a NEMA 10-50P.
I'd rather not do any welding actually inside the garage, with perhaps rare exceptions. I was thinking of installing the new outlet on the outside of the garage, at the driveway, just 2 or 3 feet from the subpanel I'm replacing. I don't currently own an RV, but it strikes me that it would be ideal to install a receptacle which could be used either for the welder or for an RV.
Suggestions? (Also, suggestions for "tuning up" and safety checking the old Miller welder prior to first use are welcomed as well.)
Best Answer
I appreciate your effort to try and combine outlets and wiring but it's usually pretty hard to do. Your welder will need a 40 Amp breaker, two hots and a ground. Your future RV would probably need at least a 20 Amp breaker, one hot, a neutral and a ground. Weather proof, water tight outlets and cover plates can run into a lot of money so I'd think about installing your welder outlet in the garage. Put a longer cord on your welder or get longer ground and electrode cables so you can weld outside. If and when you get your RV, then deal with the outside outlet. If you run 3/4" conduit and THHN for the welder circuit, you could add the new RV circuit in the conduit and extend it outside with your weatherproof/watertight fittings. If you're planning on running cable, you'd need two separate runs.
As far as testing your welder, A Megger test would be the best for verifying the insulation is good. You could also remove the access panels and clean everything up and check all the connections. Plug it in and strike a small arc at each setting.