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I plan on wiring this 30A general duty shutoff switch with 8 gauge red /black/ as two hot 120 legs and green as ground. The line will be coming from a 30 amp breaker from the main panel. The load will be to a 50amp plug for my welder. My question is do I run the ground from the plug right to the panel or should I add a ground bar to this shutoff switch for my ground. Also will having an empty pole on this switch hurt?

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  • Welcome. Please take the tour.
    – isherwood
    Jan 7, 2021 at 21:55
  • What make is said shutoff switch? Also, what's the I1eff or I1max on your welder's nameplate? Jan 8, 2021 at 0:20

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Well everything but the 50 amp plug will be ok, putting a 50 amp plug on a 30 amp circuit Would violate code per table 210.21.B.3 When you connect in the box the ground attaches to the box also. Normally a green 10-32 self forming screw fits right in one of those punched holes below the switch block. Some have a ground symbol above them. There should be a flash guard and a cover over the contacts it is kinda important and should be replaced (the flash guard these switches are known to throw molten metal).

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If you're running rigid or EMT conduit, then you can use the conduit as a ground. If running cable or wire in PVC, then the ground will have to be connected to the disconnect switch, a small buss bar would be the way to go.

You've got a lot of different numbers here. A 30 amp breaker connected to #8 AWG, which is good for 40 amps, going to a 30 amp disconnect and then to a 50 amp plug. What's the nameplate on your welder say???

Having a spare, empty leg, in the disconnect won't be a problem

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  • Guessing I should just get #6 wire and a 60 amp shutoff switch so the 50 amp plug will be in tolerance. I don't think I can get a 30 amp plug
    – Joe
    Jan 7, 2021 at 22:23
  • We can always go larger on the wire so if the welder is ok with 30 amp it could be used with a 30 amp circuit but the receptacle itself is limited to the the breaker size by table 210.21.b.3. If a larger breaker is chosen the disconnect would not be code compliant the next size up is 60a in that style. Welders are non continuous loads so they can be wired at 100% of the nameplate value even if you use it for 3 hours of more.
    – Ed Beal
    Jan 8, 2021 at 14:04

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