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. Today I discuss reverse polarity.
What happens if I have reverse polarity on a 30-amp pedestal? Can I still use it? My surge protector said there is reverse polarity, which is how I know there’s a problem. My electrician says it’s doesn’t really matter and to go ahead and plug in. Is that true? Thank you so much for your answer and making these videos!!! —Hosh
Thanks for watching my videos and asking questions. The short answer is that a reverse hot-neutral polarity in a 30- or 20-amp outlet isn’t immediately dangerous. However, it does show that whoever wired it never tested in installation and there could be other problems lurking inside that could be dangerous or even deadly.
What is “Reverse Polarity”
As you can see from this diagram, there are three conductors in a 30-amp pedestal outlet. They’re called Hot, Neutral and Ground. The Hot conductor is typically Black or Red, the Neutral conductor is always White, and the Ground conductor can be Green or Bare Copper.
And looking at the diagram above and the video below, in a properly wired outlet you should measure close to 0 volts between ground and neutral, and 120 volts between neutral and hot as well as ground and hot.
But if the Hot and Neutral conductors are accidentally reversed during installation you’ll measure around 120 volts between the ground and neutral conductors and 0 volts between ground and hot. And that’s what we call Reverse Polarity.
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Is it dangerous?
It’s not immediately dangerous, since your RV is supposed to be wired with the neutral and ground buses separated from each other. That is “unbonded” in the language of an electrician. Since that means both of them are isolated from your RV chassis, then it can’t create a hot-skin voltage.
But what if my RV is incorrectly wired and I plug into this outlet?
That’s the real danger. Since many DIY electricians have rewired RVs over the years, I’ve encountered a number of them with a bonded neutral/ground inside of the RV. If that’s the only thing wrong with the wiring, then plugging into a Reverse Polarity Outlet will immediately trip the 30-amp circuit breaker with spectacular fireworks. Here’s my video on how to test for Reverse Polarity with a standard digital multimeter. Click the picture or HERE.
However, if your RV also has a broken ground connection plus an internal neutral-ground bond, then plugging it into a pedestal with Reverse Polarity will energize the chassis and skin of your RV with 120-volts AC and at full circuit breaker (20 or 30-amp) current. That’s definitely dangerous.
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Is my electrician correct?
Well, he’s correct that it’s probably not immediately dangerous if your RV is wired properly. However, if it’s not, then a Reverse Polarity Outlet could created a deadly hot-skin voltage on the RV. And if you then touch anything metal on an RV while standing on damp or wet ground, then that fault current can go through your heart, causing it to go into cardiac fibrillation. So I would say NO, because it could be dangerous and the outlet miswiring condition needs to be corrected sooner rather than later.
I worry that any electrician who doesn’t correct any miswired campground outlet (in this case one with Reverse Polarity) and tells you to plug into it could be held liable for any damages or injuries that result from his misinformation. So he needs to correct any wiring errors immediately.
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….
Send your questions to me at my new RVelectricity forum here.
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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