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I will be installing temporary wiring for an RV which has a NEMA 14-50 plug. The RV does not actually need 240v, it just splits the load between two 120v legs. I want to use a 30A 120V circuit breaker, and put a 14-50 receptacle on the end of a cord. A common way to do this is to use a straight TT-30 cord with a 50A to 30A "dogbone" adapter, but in order to have one less connection, I'd like to wire a 14-50 receptacle directly to the cord, like this one.

My question is, how can I bridge the two hot legs inside this receptacle? Is it safe to use a short jumper wire for this?

https://www.amazon.com/gp/product/B00192QB9M enter image description here

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No. You cannot hardwire a 50A receptacle onto a 30A breaker.

Given your goals (30A single-pole breaker) use either a TT30 receptacle or a NEMA L5-30R.

You are welcome to fabricate your own dogbone adapter, with a NEMA 10-50R on one end and either a TT30 plug or L5-30P on the other.

Inside the homebrew dogbone adapter, I am OK with hooking both 10-50R hots to the same supply hot, but: Be very careful that your RV is not wired with any multi-wire branch circuits. Those will overload the neutral wire in that configuration. Because of this risk in using the adapter in random unchecked RVs, be very careful who you loan that adapter to.

  • How would I bridge both hots inside the adapter? I haven't seen the inside of one yet; is it ok to put two wires under one screw? I'm doing 14-50, not 10-50. If there were a 240 appliance, I think it would trip the breaker and be ok. – Elliott B Nov 27 '18 at 2:24
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    You have to see how it's designed, many do allow two wires under a screw. In this setup, 240V appliances simply won't work, no harm no foul. A dryer will spin but not heat. However, in a multi-wire branch circuit, google that... Two 120V half-circuits designed for neutral to only handle differential current, actually the neutral will handle the sum of both currents. And neutrals don't have fuses! – Harper Nov 27 '18 at 2:31
  • Wow that's interesting! I didn't know about MWBCs. Is there any way to tell whether an RV uses them? My homemade solution would be effectively the same as a premade dogbone, which are very common, so my guess is most RVs don't. – Elliott B Nov 27 '18 at 2:55
  • Why do you say no to wiring the 50A receptacle onto the 30A breaker? It's for my own temporary use, and if it's overloaded it will simply trip the breaker. – Elliott B Nov 27 '18 at 2:57
  • @ElliottB because it's a code violation. Code doesn't recognize "temporary" stuff, and there's a lot of history of a "I know what I'm doing" one-off becoming temporary forever, then having the same problems a permanent isntallation would have. E.g. The arrangement practically invotes "the next guy" to swap out the breaker to 50A to match the socket, oblivious to the 10AWG wire. – Harper Nov 27 '18 at 5:09

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