By Mike Sokol
Just a reminder that I’ll be presenting free seminars at the Hershey RV Show September 11-15, as well as offering a 3-hour advanced electricity seminar just off campus in Grantville, PA, on Saturday, Sept. 14. Cost for my Advanced RV Electricity seminar is $125 for everyone, but discounted to $100 for RVtravel.com paid members. Register HERE, but do it soon since the room is limited to 50 seats maximum. And now back to our regularly scheduled program.
Dear Mike,
I’ve read all the articles you’ve written about Reverse Polarity Bootleg Grounds but was unable to post a comment, since they are more than a year old!
My question, which I don’t believe was answered in the articles, is:
Are surge protector companies, like Progressive, working to fix this problem in their products so they do detect this condition?
Appreciate your comments! Thanks! —Jeff
Dear Jeff,
I’m happy to provide a few updates. But in the meantime, let’s review what an RPBG (Reverse Polarity Bootleg Ground) is and why it’s dangerous.
This is a dangerous miswiring condition that I discovered and named nearly 10 years ago, and it’s important to understand since an RPBG can sometimes be found in 1970s or earlier era houses, garages, performance stages, churches and campgrounds. If you plug your RV into an outlet miswired with an RPBG condition, then you’re creating a life-threatening condition.
But first here’s a picture of how and why this condition exists in the first place. If you look at the leftmost outlet above/left (Image 1) you’ll see that it’s wired correctly with a green/ground wire, white/neutral wire, and a black/hot wire.
All houses, stages and campground outlets since the early 1970s are supposed to be wired like that. And probably 99.99% of them are wired correctly. But if you’ve ever done any wiring in an old house, stage, boat dock or even campground, you’ll find that the green ground wires didn’t exist in the 1960s or before. That’s because code didn’t require any kind of ground at that point in time. So that’s when ungrounded 2-prong outlets were installed everywhere with a polarized plug (Image 2).
However, in the early ’70s the code changed and all new installations were required to upgrade to 3-prong grounded versions with 15- or 20-amp capacity (Image 3). But since there were no preexisting ground wires already run in the walls, some electricians and DIY guys would do something called a “bootleg ground,” which you can see in the middle outlet of the top diagram (Image 1). That is, they would simply jumper the ground screw on the back of the outlet over to the neutral wire.
While that’s a huge code violation, in many cases there’s no immediate danger, and many older installations still have upgraded grounded outlets with bootleg grounds. I’ll just note that this is a dangerous practice and any discovered bootleg ground outlets should be corrected by running new wiring that includes a ground conductor (formally called an EGC for Equipment Grounding Conductor).
However, if you do make a bootleg ground and also happen to get the Hot/Neutral polarity reversed at the same time, then you create something I call a Reverse Polarity Bootleg Ground, or RPBG for short. That’s in the rightmost outlet of the top diagram (Image 1). It’s probably the most dangerous kind of miswiring condition you’ll ever encounter since it does two things.
First, an RPBG outlet will energize the skin, chassis, tow vehicle and virtually everything plugged into or connected to your RV with a 120 volts of hot-skin/contact-voltage, and with at least 20 amps of current behind it. But the RV and all its appliances will operate normally with no warning signs of an energized surface. So no sparks, blue glow, hum, or any other special effects you might see in the movies. And any 3-light outlet tester tells you the outlet is OK, when the ground is sitting at 120 volts. There are simply no warning signs.
Second, it’s not discoverable by any standard meter test (Image 5), 3-light outlet tester (Image 4), or even the most expensive EMS surge protectors on the market. While Progressive initially told their customers that their products could detect and disconnect an RV from the hot ground voltage of an RPBG outlet, once I sent my schematics to their engineering department and had them build a test unit, they all called me back to let me know I was correct. They had never realized such a condition could exist, and their EMS surge protectors were helpless to warn you about the condition.
But I’ve personally seen RPBG outlets in at least a few dozen campgrounds, boat docks, churches and sound stages. In fact, anytime I see a brand-new 3-prong grounded outlet in an old building, I’m doubly careful to test it for RPBG miswiring since electricians still take this inexpensive shortcut, even though it’s a big code violation.
The only simple way to detect an RPBG condition is by using a Non-Contact Voltage Tester (NCVT), which is a proceedure I developed and pioneered for the RV industry. As you can see (Image 6), a NCVT will easily find an outlet that’s been miswired with a RPBG condition.
I’ve discussed this RPBG condition with every EMS/surge-protector manufacturer in on the market and currently none of their products can detect or disconnect your RV from one. However, I’ve been working on a possible solution that would allow an EMS/surge-protector to alert you of this hot-chassis condition, no matter what the cause. However, I’m under an NDA (Non-Disclosure Agreement) not to divulge any details, so I can’t discuss anything beyond the fact that I’ve done experiments and have some ideas on how to make it work. But once I can talk about it, you’ll hear details here first.
In the meantime, be sure to use your Non-Contact Voltage Tester every time you hook up to shore power to make sure the campground pedestal or garage outlet and your RV are safe from any hot-skin voltages. For those of you who don’t know what a Non-Contact Voltage Tester (NCVT) is or how to use one, read my article that includes a video demonstration HERE.
And here’s a much more technical article about RPBG miswiring I wrote for the electrical contracting industry that goes into much more details including code references. Read it HERE.
OK, I’m getting ready for the FROG Rally in Goshen, IN, next week. If you’re there please stop by and say you’re an RVelectricity reader. In the meantime, 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.
I assume things have changed since 2019. My Hughes Powerdog can detect L1/N and L2/N reversal so would catch this.
Only been 6 months, but I’m anxiously awaiting news of your RPBG detection making it into an EMS. Does your NDA allow you to say if others still think your research can make it into an EMS?
As usual Mike, you give an excellent explanation to those of us who are not proficient in electricity. Many thanks for your efforts.
You’re most welcome. I really enjoy teaching this stuff.
Mike, I just watched your 8 yr old video “Hot Skin RV proximity test full scale”,
where you measured hot skin at 40v and said that was enough to take a person down. I also watched your 5 yr old video “Review of the Amprobe PK-110 Kit for testing RV Electricity”.
I do not understand electricity well, but I think you are trying to tell us RV folks (and boat and sound stage people, too), that however the mis-wiring happened, if you are equipped with the correct non-contact voltage (NCVT) detector we will save our skins (sorry, pun).
If I understand, the Amprobe Kit you reviewed has a NCVT that measures from 90-1000v, and that is not sufficient if 40v is critical (please affirm). Also, is my simple take-away correct – if RV’s have nothing else (no voltmeter, no 3 light wiring tester), owning and using a NCVT that is capable of sensing from 12v-1000v (i.e. Klein NCVT-3 or Amprobe NCV-1040), we could quickly detect the most dangerous condition (to our lives)?
PS I would recommend pointers in your noshockzone.org, Mike Sokol channel, How-to-seminars channel and your other knowledge depots so people can find/access/buy all of the very good information you have created.
PPS If I had a copper wire running from RV metal (frame, skin, whatever) attached to copper grounding stake, and pounded the stake in every time I parked, would that eliminate me being the ground? Please excuse my lack of understanding of neutral, ground, bonding…
mark@birnbaum.us
Mark, thanks for your post. The key thing to understand about NCVTs is that even if they’re rated for 90 to 1,000 volts, they’ll actually detect as low as 40 volts AC on a large object like an RV. In fact, the Fluke VoltAlert I show in those videos is rated for 90 to 1,000 volts, and you can see that it easily identifies a 40-volt hot-skin condition. As to grounding rods, they actually do little to nothing in terms of actually grounding your RV. A properly grounded RV requires that the ground wire that’s attached (bonded) to the frame of your RV must have a solid connection (under 1 ohm) all the way back to the incoming service (circuit breaker) panel in your house or the campground.
I don’t understand image 5. If hot and ground are tied together, there should be no voltage between them. That picture looks like how I would expect a bootleg ground to look, not a reversed one.
If you look at the right-most outlet in Image 1 closely, you’ll see that the incoming white (neutral) and hot (black) wires have been reversed where they feed into the outlet. Whatever you plug into this RPBG outlet will have its own chassis tied directly to the hot wire of the circuit breaker via the ground pin of your power cord. And the neutral in your RV power cord will be tied to the incoming hot wire as well. So yes, they’re at the same voltage potential, which just so happens to be 120 volts above earth ground. And since the hot wire in your power cord is now connected to the incoming neutral wire, if you measure between hot/neutral, hot/ground and ground/neutral with a digital meter or 3-light tester, all voltages will appear correct. But in actuality, your RV power is now inverted with your chassis ground/skin at 120 volts above earth and your hot wires at 0 volts above earth. The only easy way to find an RPBG is by measuring the voltage compared to a ground rod stuck in the earth or by using a NCVT.
Thank you.
Mike,
Thanks for all of the articles on electrical wiring. They are very informative as is this one. I have a new (to me) condition I’ve just come across and its a bit disconcerting. Our current campground has 50 amp plugs “wired” for 30 amp service behind a 30 amp breaker. They say this is due to an upgrade they are working on. My Progressive PT50X surge protector kept dropping us when we used our #1 ac. The protector would read about 105 v on leg 1 and 110 v on leg 2 at mid day. They let us move to a site with slightly better voltages and the electrical service has remained on. My question is,,,, Is it safe and/or practical to wire a 50 amp plug for 30 amp service? The voltages measured drop slightly as the day heats up, so I suspect the local utility has something to do with it as well. Again thanks for all the excellent information.
There’s no danger in feeding a 50-amp NEMA 14-50 outlet with a 30-amp circuit breaker as long as it’s wired up with a 120/240-volt 2-pole feed. However, it sounds like the campground needs to replace their lighter gauge wiring with much heavier wire running to the pedestals, and the power company may need to increase the size of the transformer feeding the campground. This can easily cost a few thousand dollars per campsite by the time it’s done since there’s permits, new pedestals, new wiring run in 16″ to 24″ deep trenches, and possibly a new transformer from the power company (at least $50,000 just for that one item). But more RVs are demanding more power, so it’s a real upgrade problem for campgrounds already strapped for cash.
Thanks Mike for the reply. Highly informative info.
You’re welcome. When I first discovered and named the RPBG condition it was a real eye opener, especially when I started calling all my engineering colleagues and manufacturer tech departments. Once they built one and tried it they understood the sometimes weird and unexplained shocks and meltdowns they had seen in the field.
Thanks, Mike, for an easy to read and understand article on this. Please excuse my ignorance if this is a stupid question. Does an RPBG condition only occur on 3-prong 15/20A outlets or can it also occur on 30A or 50A outlets?
I’ve only ever seen an RPBG condition on one 30-amp pedestal that was hung on the side of a garage, so it’s certainly possible. And it should be nearly impossible to make a mistake and miswire a 50-amp outlet with an RPBG, but I’ve learned to never say never when it comes to wiring mistakes. If you have an unexplained hot-skin voltage even though the outlet tests ok, suspect a Reverse Polarity Bootleg Ground.