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Old 05-22-2015, 12:04 AM   #31
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Originally Posted by wbarnes View Post
Hi folks

I did so more testing today with one of the campground workers and we made an interesting observation but we are not able to rationalize what it means.

The campground circuit I am on has 7 campers. While each receptacle has its own hot wire, they share the same neutral. The campground worker believes the ground is bonded to neutral (bootleg ground).

We tested all the campers that are on this panel for their frame to ground voltage reading. All were about 5.4 volts. We tested the pedestal outlets and they show clean. Now the interesting observation......the receptacles are housed in a grey cabinet on the wooden pedastal. We tested the from one of the cabinet screws to the ground and it had 5.4 volts (despite its receptacle showing ground-to-neutral as 0 volts). We tested from the screw to ground with all the campers unplugged and plugged in....same 5.4 volts.

Thoughts?

Bill


Ok, now the interesting observation. W
If indeed they've wired the pedestals with bootleg grounds, then this is an easy answer. When there's a voltage drop on a hot wire due to a current draw, there's an equal and opposite voltage drop on the neutral wire (but 180 degrees out of phase). So a branch circuit that's dropped from 120 to 110 volts can have 5 volts drop on the hot wire and 5 volts drop on the neutral. That's normal, but isn't supposed to influence the ground wire. However, if the ground an neutral are bonded together in each pedestal (a code violation), then the ground bus in the outlet will biased to the same potential as the neutral voltage drop. That will show up as a variable voltage between the ground wire and an earth connection. I've seen this many times in the pro-sound industry (my main gig) and only occasionally in a campground. But sounds like that's what's going on. Please PM me directly with the campground details since what they're doing is not only a serious code violation, it's very dangers and could become a shock hazard very easily.

Mike Sokol
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Old 05-22-2015, 05:50 AM   #32
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We tested the from one of the cabinet screws to the ground and it had 5.4 volts (despite its receptacle showing ground-to-neutral as 0 volts). We tested from the screw to ground with all the campers unplugged and plugged in....same 5.4 volts.
One of the ways I test for bootleg grounds is to carefully measure the voltage between the neutral and ground contacts on an outlet while there's a sufficient load on that branch circuit to cause a significant voltage drop. Under no load there should be very close to 0 volts between Ground and Neutral. However, if you load the pedestal enough that the Hot to Neutral voltage drops from 120 volts down to 110 volts (pretty common in a campground), you should then measure between 2 to 5 volts between the Ground and Neutral. That proves that that the Neutral and Ground are not "Bootlegged" together and are indeed separate wires back to the service panel. It's perfectly normal and expected to measure around 1 volt or so between the Ground and Neutral contacts in any building or campground with electrical activity.

As I noted on my previous post you can get a $300 Ground Loop Impedance Tester that will warn you that there's not enough predicted impedance in the EGC ground wire and likely a bootleg ground.

So if under no load you're still measuring around 5 volts between your local EGC Ground (the pedestal enclosure) and the earth ground (a rod driven into the dirt), then that indicates there a bootleg ground somewhere upstream of the pedestal you're plugged into, perhaps at a subpanel or even at one of the other pedestals in your group. I'll note that you can get similar (but not exactly the same) load/no-load G-N-E voltage readings with a swapped Ground and Neutral in a receptacle/outlet. Hard to believe, but swapped Grounds and Neutrals are fairly common in residential and office wiring.

This is fairly high-level troubleshooting that few electricians will understand, which is why bootleg grounds are hard to find. If fact I spend a fair amount of my business troubleshooting why the power wiring is making sound system hum and buzz. That voltage on the ground wire is what causes something we call ground loop hum.

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Old 05-22-2015, 08:26 AM   #33
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Bill - did you ever identify when your battery was dead?
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Old 05-22-2015, 10:16 AM   #34
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I have nothing contrustive to add. Just wanted to thank all of you for this discussion, I feel a bit smarter for reading, and re-reading, the posts.
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Old 05-22-2015, 10:31 AM   #35
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Yea, I Had to re-read Mikes technical description a few times as well.
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Old 05-22-2015, 02:50 PM   #36
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Yes, it's like reading the articles in a Playboy. The pictures seem to make things clearer! LOL
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Old 05-22-2015, 04:47 PM   #37
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There are articles in playboy?
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Old 05-22-2015, 05:02 PM   #38
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Yea, I Had to re-read Mikes technical description a few times as well.
I know it seems mind boggling, but even complex electrical circuits are just a bunch of simple circuits connected together, just like a steam locomotive is a bunch of simple levers and pistons that perform a complex function. In addition to studying Electrical Engineering in college, I also liked to set up my own experiments that showed basic electrical principals like voltage drop due to current flow, etc... While you can do this all with equations and schematics (and I often do), it's really enlightening to design a demonstration you can have right in front of you on a table.

The problem with electrical distro circuits is that not a lot of people want to play with this stuff, and probably shouldn't be messing around with live 120-volt circuits anyways. However, since I'm trained in electrical safety and often work on live circuits for pro-audio distribution, I can do these experiments with minimal danger to myself. So kids, don't try this at home.

If you're curious, here's one of my portable No~Shock~Zone demonstrations that allows me to hot-skin electrify the chassis of pro-sound gear as well as create and mitigate ground loop hum at will. Mike Sokol: Electrical Shock Prevention in Sound Systems - B&K Precision I also have a No~Shock~Zone seminar designed for RV power safety where I hot-skin energize an RV to various voltage to show how it can be detected and corrected. Let me know if you think that Jayco would like me to do a NSZ demonstration at a Jayco camp meeting on the east coast.
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Old 05-22-2015, 05:52 PM   #39
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Hi Mike et al,

I am heading out to the campground tonight and will post more details once I have an update. They had scheduled a "bonafide" electrician today to investigate; but I have not yet had an update.

Mike, you made a comment that has made me go "hmmmm". You mentioned about a ground loop hum. Coincidentally; last weekend; we had a loud audible hum coming from the TV set speakers that was drowning out the audio of the movie coming out of the surround sound RV speakers. I haven't had chance to assess the "why" but noted that if the Composite L/R cables from the stereo system are pulled out, the hum stops. Now I am wondering if anything to do with the issue I have on the HotSkin.

Bill
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Old 05-24-2015, 07:03 PM   #40
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The campground had the electrician come in Friday. Although I didn't speak with them directly, I am told that it is acknowledged that something is not right; they just don't know what exactly is causing it.

I have shared Mike's articles and this discussion thread with them in hopes that it may help point to the issue.

I redid some tests (RV Frame to Ground, Pedastel box screw to ground) and they are now showing 12 volts; up from the previous 5-7 volts. This would seem consistent and expected based on the Mike's last post indicating that as voltage drop occurs on the hot; an equal increase occurs on the neutral. Assuming bootleg ground (as was indicated by the installer); then I would expect this voltage increase to show on the RV frame.

Hoping this week brings more investigation and resolution.

Bill
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