What is polarity?

What is polarity?

 

Mike,
I hear the word “polarity” a lot, but what exactly is it? Doesn’t the AC power line reverse its own polarity 60 times a second? If so, how does Reversed Polarity cause a Hot-Skin condition? And why do they call it a Hot-Skin condition? Does it electrify anything else other than the RV skin? —Bobbie

Non-polarized plug

Bobbie,
You are sort of correct, but not exactly. However, I hate the word “polarity” when referring to AC power. That’s because an AC outlet actually reverses its own polarity 120 times per second for 60 Hz power in the U.S. (it’s 50 Hz in much of Europe). But the RV industry uses Reversed Polarity to describe what’s actually reversed Hot and Neutral wiring. I think that’s because in the ’40s and ’50s there was something called a non-grounded “polarized plug” on radios and home appliances. And those early appliances lacked input transformers, which bonded the incoming neutral wire directly to the chassis. So if the “polarized plug” was flipped, reversing its “polarity,” then the radio chassis was connected directly to the hot wire, which could be lethal.

That’s why all modern appliances have some sort of power transformer to isolate their own chassis from the power line. The exception is double insulated power tools and things like hair dryers with GFCI plugs. And all RVs are supposed to be wired with the neutral and ground isolated from each other. So with all modern appliances and RVs, it really doesn’t matter if the hot and neutral (H-N)  wires are reversed. There are tons of old wives’ tales that swapped H-N lines somehow burns up on-off switches, or causes an appliance to use more electricity, or hum, or whatever. But that’s all incorrect information. The REAL danger is that troubleshooting a system with the neutral wire energized to 120-volts can be deadly to the technician doing the testing.

Pedestal testing

So why should you care if your RV outlet shows reversed polarity? Well, if you have a second miswiring condition in your RV, specifically an internal Ground-Neutral Bond, it’s possible for a reversed H-N outlet to create a hot skin condition. Also, it shows that whoever wired the electrical outlet doesn’t know what they’re doing and could have made other mistakes. So don’t accept reversed Hot-Neutral outlets on a pedestal since it’s an obvious mistake that should be corrected.

One of the things I’ve pitched to the RVIA and various inspection agencies is the idea of testing RV pedestals for proper grounding and “polarity” yearly or maybe every other year. And I think they should also be retested anytime there’s been a repair done on a pedestal. But it’s slow going since nobody wants to spend money, even if it is for safety.

And if you want to know how to properly test your own campground pedestal for proper voltage and polarity, here’s a video I made on that topic.

BTW: I don’t like the term “RV hot skin” either, since it’s really a hot-chassis condition that also spreads to the RV “skin.” So a hot-skin condition creates voltage not only on the “skin” but also on the RV’s wheels, trailer hitch, the tow vehicle, door handles, metal steps, etc. That’s why an RV hot skin is so dangerous. Virtually anything metal on an RV is tied to its chassis. So if the chassis is electrically charged, then EVERYTHING is charged with a shock voltage.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

##RVT800

 

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4 thoughts on “What is polarity?

  1. Mike Sokol

    If this is a Honda EU2000 generator, then you should be able to use a G-N bonding plug which I’ve discussed on this website many times. For more information see https://rvtravel.com/how-generator-neutral-ground-bonding-for-an-rv-works/ and http://noshockzone.org/generator-ground-neutral-bonding/

  2. Mike Sokol

    This really has nothing to do with a lack of ground to the soil. It’s because the inverter has a floating neutral that’s isolated from the chassis ground. Again, the word ground is a poor one since it’s really a “bond” between the chassis ground and neutral. While the RV’s electrical system must maintain separated neutral and ground wiring, a generator, inverter or power pedestal does, in fact, create a ground-neutral bond. Now be aware that some inverters won’t tolerate their neutral and ground being bonded, so check the manufacture’s documentation. But most of the time the transfer switch is supposed to create that bond when in inverter mode.

    1. RV Staff

      You’re so smart, Mike! I’m hoping that some of your electrical wisdom rubs off on me — I’m scared to death of electricity (and spiders)! 😯 —Diane at RVtravel.com

  3. George

    When I run my portable 2000 watt invertor generator, my 3 light plug-in tester shows I have an open ground. I’ve accepted this as normal in not having a ground rod into the soil. Is this “normal” and is there a way to correct that without burying a grounding rod? Also, is it dangerous?

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