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I have a three phase, 30amp, 240 volt circuit that is feeding two three phase, 20amp welding receptacles. I would like to change out one of the receptacles to a 20 amp, 240 volt three wire receptacle (only utilizing two of the legs to feed a plasma cutter.

Can anyone direct me to a place in the NEC that would prohibit me from keeping them on the same breaker?

All wire is #10awg

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  • Unsure about three phase circuits, but on common 120/240 circuits the receptacles match the breaker rating. 30 amp breaker equals/must have 30 amp receptacles, not 20 amp rated receptacles.
    – crip659
    Apr 5 at 14:32
  • Would a 20 A, 240 V, three-wire receptacle include a neutral? Or does three-wire mean 3-phase?
    – Jim Stewart
    Apr 6 at 17:47

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Wow, we don't hear questions involving 3 phase 240 very often. It's a wild- or high-leg delta, then, with the orange coloring and all that?

Table 210-21(b)(3) is what you're looking for. It indicates which combinations of receptacles and breakers are allowed. It also confirms that multiple receptacles are generally allowed. For circuits having two or more receptacles:

NEC Table 210.21(B)(3)

The present use of 20 A receptacles on a 30 A circuit is non-compliant.

So far as keeping all of these on the same breaker, the maximum cord-and-plug connected load is 80% of the circuit breaker limit, which would be 16 A after you swap that 30 A breaker down to 20 A to match the connected receptacles. You'll have to sum the load of the connected devices and find out whether it exceeds 16 A. If so, multiple circuits are required.

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  • Doesn't necessarily have to be high-leg. Could be an open delta with no neutral. Straight 240V all the way around (not that it matters in the OP's context since he doesn't appear to want or need 120V).
    – Chris O
    Apr 5 at 17:11
  • Thank you. Yes, I am planning to change out the breaker to a 20 amp, I just don't have room in the panel for an additional dedicated breaker.
    – Taddy
    Apr 5 at 19:16
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    @Taddy You'd have to change all the sockets, and all the plugs on the appliances using them. You can't have 30A sockets on a 20A circuit. How about using your last 3 spaces to feed a subpanel? Then you could add any circuits you want without counting panel spaces, which sucks and is easily avoided. Greg feel free to use this graphic. i.stack.imgur.com/yfeFM.png
    – Harper - Reinstate Monica
    Apr 5 at 21:30
  • @Harper-ReinstateMonica I think you misread OP: there's a 30A circuit and existing 20A receptacles, one of which is proposed to be changed for a different kind of 20A receptacle. And thanks for the image, that does look nicer than my bullet list.
    – Greg Hill
    Apr 5 at 22:38
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    Is it possible that the current setup is fine? Welders are special in the NEC and it’s normal for them to have larger OCPDs than normally allowed.
    – nobody
    Apr 6 at 11:11

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