RVelectricity – Just Ask Mike (J.A.M.): Accidental reversed polarity adapter

By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. This week I answer a reader’s question about a hot-neutral reversal in his RV’s shore power cord-set.

Where does all the time go?

Dear Readers: Here’s a typical help session I do all the time in the background. While it appears that I sometimes take a very long time to answer questions, that’s only because I get dozens of direct email questions just like this every week. Sorry, but I don’t give quickie answers since you’re all depending on me to keep you safe. So it does take time for me to carefully consider each question and come up with a safe answer.

And that doesn’t begin to scratch the surface of what my moderators and I cover every week in my RVelectricity Facebook Group. There’s a lot to answer for the RV groups since electricity is both mysterious and dangerous. I try to demystify it as well as keep you all safe.

Let the Q&A begin… about a reversed polarity adapter

Dear Mike:
I sent a question to the NoShockZone; it was there then disappeared. At one end of my trailer I have a 50-amp shore power; the other end I put in a 30-amp plug for my generator divided by a transfer switch. Both ends test good on the trailer with a three light tester.

I have a Yamaha EF3000iSEB. Testing per your video it shows an open ground. When I install the n-g plug it shows good. But when I hook the trailer to the generator, the trailer shows an open ground. When I install the n-g plug the trailer shows hot/neutral reverse indication on the tester. Any ideas? Thanks. —Ron

My first answer regarding a possible hot-neutral reversal

Dear Ron: I think you have a hot-neutral reversal somewhere in your RV’s shore power cord-set. You need to confirm that the 30- to 50-amp adapter is properly wired. Is this a purchased cord, or something that was DIY built? —Mike Sokol / No~Shock~Zone

Back from Ron

Dear Mike:  The 30-amp cord was made by me. 50-amp came with the trailer. I’ll check the cord out. Thanks. —Ron

More from me…

Dear Ron: Those 30-amp TT-30 plugs are very easy to wire with the hot and neutral reversed. Here’s how the receptacle wiring should be oriented – looking at the back of the plug.

Your 30-amp plug should look the same from the back. And note that the neutral screw will be white, with the hot screw being brass/gold. —Mike Sokol / No~Shock~Zone

Bingo… It was a hot-neutral reversal

Dear Mike: You were right. I found that when I installed a different plug on the generator itself, I had reversed the wires. All is good with the n-g plug. Thanks for the help. —Ron

Wrap it up…

Please be aware that a reversed polarity shore power plug or adapter (hot and neutral reversal) by itself WILL NOT cause a hot-skin voltage on your RV. For that condition to occur you need to have a failed ground conductor or connection. More on that topic in a future JAM session.

And I’ll be sure to cover how to properly Neutral-Ground bond your Inverter Generator in an article soon. Much to teach…

Bye, bye…

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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