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I'm hoping to run two 240 V 50 A outlets for an ARC welder. One will be outside and the other inside the shop. If I install a double pole double throw switch such that only one receptacle can be energized at a time, would the two receptacles be allowed by NEC to be on a single breaker in the load center?

  • Is this shop attached to your house, or a separate structure? – ThreePhaseEel Oct 28 '17 at 15:58
  • Attached. It was a garage; hasn't seen a car in over a decade – John Sonoran Oct 28 '17 at 16:59
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When properly sized the breaker is sized to protect the conductors and will not allow you to overload them.

Consequently, you can put as many receptacles on a circuit as you want and if the circuit is overloaded the breaker will protect it.

You don't need a switch, especially if you only have one welder since you can't use more than one receptacle at a time anyway.

Just parallel the outlets and you are good.

Just to add some context here are some pertinent Code articles:

210.19(A)(2) Branch Circuits with More than One Receptacle. Conductors of branch circuits supplying more than one receptacle for cord-and-plug-connected portable loads shall have an ampacity of not less than the rating of the branch circuit.

And

210.21(B)(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.

Exception No. 1: Receptacles installed exclusively for the use of one or more cord-and-plug-connected arc welders shall be permitted to have ampere ratings not less than the minimum branch-circuit conductor ampacity determined by 630.11(A) or (B) for arc welders.

This last one means if the welder has a duty cycle the circuit can be downsized.

Good luck and stay safe!

  • Code has a section for each of 15, 20, 30, 40 and 50A where they break out what you can do with each type. We have long searched for a code that prohibits multiple receptacles on a 30A but have not been able to find it. Ithought there was such a prohibition for 50A, but don't have my code book in front of me. – Harper Oct 28 '17 at 18:00
  • @Harper yeah I looked all over in that article and it is a little murky. It is possible 210.23 (C) prohibits anything but cooking appliances that are fastened in place in a dwelling unit on a multiple outlet branch circuit. I don't see why it would be prohibited but if you are in an area that has a real sticky insoector they might cite that section. – ArchonOSX Oct 28 '17 at 20:24
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    @ArchonOSX -- yeah, if it were in the dwelling unit proper, 210.23(C) would apply, but a residential garage isn't part of the dwelling unit proper (it's a U occupancy type vs. the R-3 of a single family house if you ask the IBC) – ThreePhaseEel Oct 28 '17 at 21:19
  • I managed to find a 2011 NEC which is the one cited in my locale. I can't find anything that contrary what you kind contributors have said. I'm not sure whence came the one receptacle myth...Thanks! – John Sonoran Oct 28 '17 at 21:42
  • I would not downsize the wires to any receptacle, welder or not. If you run #8 to that NEMA 14-50 that's for a welder because 630.11 says you can, what happens when uncle Jimbo visits with his RV, plugs into your welder terminal and pulls 47A at 100% duty cycle? You can't voucn for what someone will plug onto a receptacle. – Harper Oct 29 '17 at 5:19
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I would not recommend two welding receptacles say rated at 50-Amps on a single circuit made up of #8 wire on a 50-amp breaker. The breaker is not there to protect against stupid. The double throw switch would be one way to deal with the issue. However, given the cost of that type of thing I expect that a second circuit may cost less.

  • Better order some of these amazon.com/Mommys-Helper-Outlet-Plugs-Count/dp/B00081J3N6 and some glue to keep them in place then. Lest you plug in more than one device on a 5-15 outlet circuit. – Billy C. Oct 29 '17 at 2:38
  • I wouldn't suggest putting #8 on a 50A breaker unless you really know what you're doing, by which I mean 630.11. – Harper Oct 29 '17 at 5:15

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