RV Electricity – Can reversed polarity shock you?

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Dear Mike,
Your No~Shock~Zone articles are some of the best I’ve ever read about RV electricity. Thanks for educating all of us “non-electrical” types.

So here’s my question: During a trip on my boat to the Erie Canal, we had one guy checking electrical outlet polarity, something I never really quite understood. He found many outlets with the wrong polarity but didn’t seem too worried about it. So can a reversed polarity cause a hot-skin shock? –Fred S.

Dear Fred,
I often get this question asking if reversed polarity can cause a hot-skin condition that can shock you. And the short answer is “not now, but it used to.” At least it did prior to the 1960s. So let’s take a quick trip in the way-back machine to review exactly what is reverse polarity and why it’s not an immediate danger nowadays.

In the early to mid 1900s there were no polarized outlets in homes. Every electrical plug and outlet had the same size slots on both sides so you could insert a non-polarized plug either way. This effectively reversed the two “poles” of the receptacle, and hence the term”pole-arity.” There was a 50-50 chance that the plug had been inserted with “reversed polarity” which have would indeed created a hot-chassis condition on some appliances. And it could definitely shock you.

I think this is where the idea that reversed polarity on a plug would energize a RV chassis with a hot-skin voltage. It was 100 percent true back in the first half of the 20th century, but not now.  That’s because the electrical code guys got smart and required plugs and receptacles be made with two different size slots that could only be plugged in one way. So now the taller slot is neutral, and the shorter slot is hot. This prevented you from plugging in something with reversed polarity. Later in the 1960s, isolation transformers and double insulation were added to all household tools and appliances, so that even an outlet accidentally wired with swapped white and black wires internally couldn’t create a hot-skin shock hazard.

Eventually , safety grounds were added to everything, and we now have the modern 3-prong plug and outlet we all know and love. And there’s no way it can be plugged in with reversed polarity, unless the electrician who wired it got his wires crossed (literally). But even if that does occur the electrical code is designed so well that under normal circumstances simply swapping the hot (black) and neutral (white) wires inside an electrical outlet still can’t create a hot-skin voltage on an RV. Yes, an inexpensive outlet tester like the Southwire unit on the left does a great job of identifying reversed polarity outlets – as long as it’s not an RPBG (Reverse Polarity Bootleg Ground) which I’ll cover in a future article.

So in the final analysis a reversed polarity outlet isn’t immediately dangerous because modern appliances have isolation transformers and double insulation, plus all RVs have their neutral and ground wires separated in their power panel. It’s only when the shore power ground wire is broken or disconnected and a leakage occurs that a hot-skin voltage is possible on an RV. However, a reversed polarity outlet in a pedestal is a sure sign that it was never tested after installation and wouldn’t pass inspection, so who knows what else is wrong? And just two wrong things in an electrical circuit can create a deadly hot-skin condition. So report all reversed polarity outlets and get them corrected. It’s the right thing to do…

Let’s play safe out there….

 

Mike Sokol is an electrical and professional sound expert with 40+ 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.

##RVT832

 

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Tommy Molnar
2 years ago

We use one of those little circuit testers similar to the one you picture (though much older, I’m sure). When we first arrive in a ‘park’ we plug it in to see if everything is ok. Lately it seems like the instant we plug the tester in inside our trailer the GFI plug pops out. Wifey then takes the tester and plugs it directly into the GFI receptacle and all is fine. But plugging it into any other plug on the GFI circuit pops the outlet. This is a relatively new thing going on. Our trailer is a 2012.

John Petruccelli
2 years ago

I had an instance where my Surge Guard detected a “reverse polarity” situation on a 30 amp outlet. Come to find out, the outlet had been wired for 240v not 120v when I got this reading. The person that had plugged into this outlet before me had “fried” their GFCI outlet and the ac side of their 3 way refrigerator. The dc mode and gas mode of the refrig still worked. The skin of the camper was fiberglass and therefore was never “hot”. Motto: Learn from others mistakes will save you $$$$$.

Mike Sokol
2 years ago

I’ll have to wire up a 120-volt outlet with 240 volts and plug in a few 3-light testers to see what happens. It appears that 30-amp outlets miswired with 240 volts are way too common.

ScottA
2 years ago
Reply to  Mike Sokol

I’m afraid you may be right. I hired an electrician to put in a 30amp at my house. I got a wild hair and decided to check it… Yup, 240 volts.

He came back and fixed it but it could have been bad if I hadn’t tested it!

Steven Scheinin
2 years ago

Ah! You give away your age and the fact you use to watch Rocky & Bullwinkle.

Mike Sokol
2 years ago

i’m not sure I understand the Rocky & Bullwinkle reference. What am I missing???

Wayne
2 years ago
Reply to  Mike Sokol

Sherman and Peabody used the “Wayback Machine” for travels through history. A segment of the Rocky and Bullwinkle Show.

Onwego
2 years ago
Reply to  Mike Sokol

He’s referring, I think, to the reference to the “way-back machine”.