Important - check this every time you set up |
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
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Topic: Important - check this every time you set up Posted: 20 Aug 2016 at 7:00am |
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There's a phenomenon I call a Reflected Hot-Skin condition where a Hot-Skin voltage on one RV in a campground can "Reflect" to others in the same loop. But that can only occur if the campground pedestals have an incorrect ground to begin with.
Here's how it works.... Imagine you you have pedestals hooked up on a common feed from the campground's service panel. This is called a "daisy chain" connection. There will be common hot1, hot2, neutral, and ground wires interconnecting all these pedestals. Since the "ground" wire is supposed to be bonded to the service panels Ground-Neutral-Earth connection, any hot-to-chassis current leakage or short inside of a single RV can only go to this "ground" where it will be drained away or trip the RV's circuit breaker. That's exactly how it's all supposed to work. In a properly grounded system it's impossible for any chassis to develop more than a volt or two potential above earth-ground, no matter what kind of other failure occurs. Now assume there's a break in this pedestal ground wiring on its way back to the service panel's Ground (G-N-E bonding point). Now if one of the RVs develops a short between line-and-chassis the current will have no path to "ground" and it will electrify the entire ground wire interconnecting all the pedestals and RVs together. So anything with a ground wire plugged into one of these pedestals will have its chassis electrified to 120 volts, creating a Hot-Skin condition. The really dangerous thing about this mis-wiring condition is that because the voltage is feeding into your RV from the ground wire, even shutting off the pedestal or RV circuit breaker can't stop it. And there's no EMS products on the market that can disconnect you from this hot-ground since electrical code does not allow the manufacturer to put a relay contact in the path of the ground wire (officially called the EGC for Equipment Grounding Conductor). However, the EMS will detect the hot-ground condition and shut off your RV's live voltage. So it will appear that you have no AC power from your EMS, while in reality your RV's ground is the only thing electrified. I've only heard of perhaps half a dozen campgrounds with this non-grounded EGC problem, which allowed a Reflected Hot Skin Condition to occur. While this is a very rare problem, it's still something to be aware of and can easily be detected with a NCVT at any time. If you ever feel a tingle, stop what you're doing and immediately test for a hot-skin voltage. If you do measure one, disconnect from shore power until the problem is resolved. |
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mike@noshockzone.org
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Pilot
Groupie Joined: 26 Jul 2015 Location: Pinckney, Mi Online Status: Offline Posts: 91 |
Post Options Quote Reply Posted: 20 Aug 2016 at 8:18am | |
Do we keep a list of problem campgrounds? Should we?
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Walt & Lynne
2015 r-pod 177 08 F150 or 2014 Explorer Pinckney,Mi |
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Rustler
Senior Member Joined: 07 May 2016 Location: S. Oregon Coast Online Status: Offline Posts: 100 |
Post Options Quote Reply Posted: 20 Aug 2016 at 6:14pm | |
Thant's an interesting situation, Jim. So I'll need to be watchful. For that condition I suppose one of those 3 light testers would show if the campground had an open ground. Also something like the progressive Industries EMSHW30C would have detected the open ground situation and have disconnected. I wonder if an RV with reverse polarity bootleg ground (RPBG) wired outlet can affect other RVs connected to the same campground. It seems that the CG's properly wired ground would cause the faulty RV's hot ground line to trip a breaker somewhere. But maybe not since the ground line doesn't have a breaker on it. Yet the faulty RV had better have a circuit breaker on its hot line, which is now connected to CG's ground. So a related question is this: Can a single RPBG-wired outlet affect other properly wired outlets within the same RV or other RVs connected via a campground electrical system?
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Russ
2009 Toyota RAV4 V6 w/ tow package 2016 Rpod 171 HRE |
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
Post Options Quote Reply Posted: 20 Aug 2016 at 8:15pm | |
Actually my name is Mike not Jim. The JM in JMSOKOL is for John Michael, which only grade school nuns and cops call me. Hah! To answer your question, an RPBG in an RV CANNOT cause hot skin voltage in any other RVs in a campground as long as the campground wiring is properly grounded. In the case of an open ground path to the service panel Neutral-Ground bond, a 3-light tester will indicate an open ground, but it won't tell you the ground is Hot. Mike Sokol |
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mike@noshockzone.org
www.noshockzone.org |
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Rustler
Senior Member Joined: 07 May 2016 Location: S. Oregon Coast Online Status: Offline Posts: 100 |
Post Options Quote Reply Posted: 20 Aug 2016 at 8:29pm | |
Thanks, Mike. So to wrap my brain around the issue is this the recommended procedure?
Is item 1 unnecessary if 2 and 3 are employed? If a single outlet is wired with RPBG, but other outlets are wired correctly (say at home or in an RV), could that situation go undetected without a circuit breaker tripping? Thanks so much for your patience in helping those of us a bit electrically challenged!
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Russ
2009 Toyota RAV4 V6 w/ tow package 2016 Rpod 171 HRE |
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techntrek
Admin Group - pHp Joined: 29 Jul 2009 Location: MD Online Status: Offline Posts: 9059 |
Post Options Quote Reply Posted: 20 Aug 2016 at 9:39pm | |
Don't forget to use the NCVT on the chassis.
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Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
Post Options Quote Reply Posted: 21 Aug 2016 at 7:00am | |
I would still use a 3-light tester as the first check of the outlet. If it won't pass that simple test, then don't plug in. Then use an NCVT to detect a hot-ground from a RPBG. And having a EMS in the circuit will protect you from over-voltage conditions. After plugging in your RV's shore power line, do a final test with a NCVT to confirm that you don't have a break in the EGC ground conductor of any extension cords of internal chassis-ground bonds inside your RV. This entire test sequence should only take a minute or two at most. Mike Sokol |
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mike@noshockzone.org
www.noshockzone.org |
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
Post Options Quote Reply Posted: 21 Aug 2016 at 8:00am | |
You're only as safe as what you plug into. Read this email I received from another reader below.
Mike Sokol We were at a function where the power for the Rv was supplied by them via a 100 amp 3phase construction type temporary power box with multiple 20 amp plugs and some larger plugs I plugged in the Rv and all was good a second trailer plugged in and it was fine when the third trailer plugged in the lights and ac would almost shut off and then become extremely bright I went to see what the problem was and found the cord feeding the construction power box was arcing at the connection to the building I pushed it back into the plugin and the surging stopped the next morning I noticed the fridge had stopped working so I plugged it in to the other receptacle on my power cord it instantly electrified the trailer and almost killed our dogs and injured my wife it turns out the fridge electric heating element blew up and welded itself to the fridge I had the trailer checked by a certified master electrician and he said there is nothing wrong with the wiring or my power cord the construction power box label clearly states that all 20amp plugs are gfi protected why did this happen? Would the power surges cause the element to self destruct? The other 2 trailers also suffered damage 2. 30 amp breakers the microwave and the cooling fan for the inverter thanx |
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mike@noshockzone.org
www.noshockzone.org |
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Bugout
Senior Member Joined: 01 Jan 2017 Location: S caroline Online Status: Offline Posts: 117 |
Post Options Quote Reply Posted: 12 Jan 2017 at 1:24pm | |
I read this thread thread the day all 16 pages.Today I was called out to put a50 amp outlet in for a food truck job went fine did the rcvt test no problems then I went inside to talk to the owner since I had rcvt in hand I ran it over metal in the truck and found the outside of the icebox was hot. It came down to a home made extension cord. If not for this thread I would never thought of this. Thanks guy.the owner of the thanks you to
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Jk Aiken South Carolina 2016 178 Toyota Tundra 2017 4.6
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
Post Options Quote Reply Posted: 12 Jan 2017 at 2:33pm | |
Glad I was able to help. Just about every electrician and technician has a Non Contact Voltage Tester, but most of them don't realize how great they are at finding a hot-chassis condition from a broken ground connection, many times caused by a mis-wired or broken extension cord.
Let's play safe out there... |
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mike@noshockzone.org
www.noshockzone.org |
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