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The dog bone isn't the problem. It causes the problem. It connects the same phase to two conductors in the cable running to the trailer with only one neutral. That isn't allowed. Each conductor with the same phase has to have it's own neutral. (I may have cited the wrong code section earlier)

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From a safety standpoint there can only be a maximum of 30-amps current on that neutral conductor which is rated for 50 amperes, so there’s no overcurrent possibility. There’s probably an exception listed in NEC 1132 or 1134 since these adapters are everywhere.

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Wouldn't National Electrical Code Article 366.20 prevent the use of such a dog bone device? 366.20 stipulates that only 1 conductor per phase can be run in a cable.

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May 7, 2023·edited May 7, 2023Author

I’m not sure what you’re asking. There is a single-pole conductor from the single-phase service in the cable that’s fed by the TT-30P connector. That single non-grounded current carrying conductor is jumpered between the two poles of the NEMA 14-50R connector. I don’t see any code violation, and there’s probably millions of these dogbone adapters in the field, many of which are UL listed.

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