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I have a 4-wire 240VAC 50amp outlet in my garage. I want to create an 50+' extension cord to my welding cart that has a 220-240vac Welder, 220-240vac plasma, and I'd also like to have a 120VAC service outlet to run a grinder or chop saw. Only one device of any type would be used at one time. I was thinking of putting a row of metal boxes on the back of my cart with the one plug 'in' and then the three 'outs' to short cords on the cart.

Can this be done and what is the wiring look like? Thx

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Yes it can be done, and yes there are conditions on the "how." Following are a few thoughts that come to mind.

  • Use the right kind of cordage (ie not building wiring like NM cable). SOOW is a good choice.
  • The 50 amp circuit is going to require heavy cord (6 gauge). If you don't really need 50 amps (and you probably don't).. you could consider changing out the breaker to 40 amps and using 8 gauge cord instead.
  • Having multiple sockets on the cart is a little tricky because of the details of joining multiple 6 or 8 gauge conductors. The outlets probably will not be designed for having two conductors landed on each terminal, so daisy-chaining the outlets won't work. You'd have to use connectors like the Polaris brand.
  • The 120 volt socket on the cart is tricky. It's obviously unsafe to wire that in such a way that it's fed directly from the 50 amp circuit. Unfortunately I don't know the details of how to accomplish this objective while strictly meeting code. I confess that I've put such a socket on my welder cart, too.. I protected it with a 20 amp fuse installed inside the junction box. A panel-mounted fuse holder or circuit breaker would have been a nicer solution.
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On job sites and at fairs and other temporary settings, a spider box is used to break out a portable feeder cable with e.g. 120/240V 50A to various other receptacles for equipment.

The box obviously must have circuit breakers for safety and code compliance. UL-listed units are available from major manufacturers. Spider boxes can be rented from any big equipment rental yard.

job site spider box

Entertainment / event production companies use rack mount versions of spider boxes.

rack mount spider box

I would not recommend this for casual use in your garage because they're bulky.

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