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At our studio we have a NEMA 14-30R outlet used for our kiln. When not in use, we want to use another piece of equipment that has an L6-30P plug. I believe the equipment is rated at 8AMP 240V.

I built an adapter that has a 14-30P on one end and an L6-30R on the other, capping the neutral inside the L6-30R. In this way we can switch from one piece of equipment to the other without running a new line, guaranteeing mutually exclusive use of the circuit.

Is this configuration safe? Would I be better off pulling off the neutral pin from the 14-30P? Right now I just want to make sure no one is going to hurt themselves until we can find an appropriate solution although running a new circuit is not an option - maybe sub-panel with a switch between two outlets?

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Your adapter is probably safe. However, I would have used a 3 conductor cable instead of a 4 conductor cable; that way there is no neutral to cap.

Another option would be to cut the plug off the end of the other piece of equipment and wire on the 14-30P.

A third option would be to wire up an 14-30 receptacle right next to the existing L6-30 receptacle, using the same circuit. As long as you are using only the kiln or the other equipment and not both at the same time, that's fine. If you really wanted to prevent both from operating at the same time, you could get a transfer switch, but that's probably overkill.

  • If I wire up two receptacles on the same circuit what is the risk if someone unwittingly tries to use both? Assuming a working breaker, will the breaker go, or the wiring overheat? – Steven Sep 7 '16 at 14:32
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    If the wiring and the breaker are both appropriately sized, then the breaker should trip. An occasional trip should not be fatal for the breaker. Have you looked at the ratings on the kiln? How many amps does it actually draw? – longneck Sep 7 '16 at 15:34
  • I'll check next time I'm at the studio. I hadn't realized I could share the circuit but of course we do that with 120V outlets all the time. – Steven Sep 8 '16 at 15:32
  • @Steven I believe it would be illegal to have two or more receptacles on a 30-50A circuit. However, when I tried to confirm that in the Code, I could not find where it said that for a 30A circuit specifically. – Harper Sep 9 '16 at 7:22
  • @Steven: The 15A-20A receptacle is, for better or for worse, something of a "universal small appliance" size, so the fact that a device has a 15A plug in no way implies that it is expected to draw even 1% of that. By contrast, the presence of a 30A plug on a device would usually imply that it's expected to draw more than 20A (or else it would have used a 20A plug). I would think that it should be possible to wire a selector switch so only one receptacle or the other could be powered, but I don't know if any such switches are UL approved. – supercat Jul 14 '18 at 14:24

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