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[GMCnet] shore power... shock! [message #250114]

Mon, 19 May 2014 12:17

Ek_Lektro

Messages: 167
Registered: March 2011

Karma: 2

Senior Member

Well, Here's a head-scratcher for ya...
And despite my "Eklektro" email handle, I'm not formally schooled in 110v electrical, so any advice appreciated! (and if this problem wasn't so intermittent, then maybe i would've solved it by now)

Sometimes when i'm plugged into shore power, i'll get a shock by touching most metal
parts on the RV (door handle, bumper, alcoa wheels, etc). I measured it with the voltmeter (with positive lead on the metal and negative buried into driveway dirt), and its fluctuating between 30 to 60 volts, AC... enough to raise your hair a bit!
The problem never happens when i'm inverting 110 volts,
(and maybe its a coincidence, but it seems to be more prevalent when the driveway is a little wet).

Here are a few possibilities / wild guesses...
- possible fault with the grounding at my garage's 110 volt service? I know that my landlord had done some re-wiring a while back...
- possible fault with the extension cord (i'll see if i can get another heavy 50 footer, to test it out)
- possible incorrect wiring when my old Onan bit the dust, and i recently had a Generac put in,
wired to the same original heavy-duty outlet
And yes... The main problem is that I can't seem to get it to consistently misbehave...

OK, thanks much for any insights,
Greg / Los Angeles / 78' Eleganza II (and '76 Birchhaven 21-foot custom cut-down)
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Re: [GMCnet] shore power... shock! [message #250116 is a reply to message #250114]

Mon, 19 May 2014 13:06

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Ek_Lektro wrote on Mon, 19 May 2014 12:17

Well, Here's a head-scratcher for ya...
And despite my "Eklektro" email handle, I'm not formally schooled in 110v electrical, so any advice appreciated! (and if this problem wasn't so intermittent, then maybe i would've solved it by now)

Sometimes when i'm plugged into shore power, i'll get a shock by touching most metal
parts on the RV (door handle, bumper, alcoa wheels, etc). I measured it with the voltmeter (with positive lead on the metal and negative buried into driveway dirt), and its fluctuating between 30 to 60 volts, AC... enough to raise your hair a bit!
The problem never happens when i'm inverting 110 volts,
(and maybe its a coincidence, but it seems to be more prevalent when the driveway is a little wet).

Here are a few possibilities / wild guesses...
- possible fault with the grounding at my garage's 110 volt service? I know that my landlord had done some re-wiring a while back...
- possible fault with the extension cord (i'll see if i can get another heavy 50 footer, to test it out)
- possible incorrect wiring when my old Onan bit the dust, and i recently had a Generac put in,
wired to the same original heavy-duty outlet
And yes... The main problem is that I can't seem to get it to consistently misbehave...

OK, thanks much for any insights,
Greg / Los Angeles / 78' Eleganza II (and '76 Birchhaven 21-foot custom cut-down)

I don't have any other suggestions of where to look, but where can I find pictures of your 21' custom cut-down?

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Re: [GMCnet] shore power... shock! [message #250117 is a reply to message #250116]

Mon, 19 May 2014 13:14

appie

Messages: 902
Registered: April 2013
Location: denmark

Karma: 2

Senior Member

Firsth would be to check your house ground a faulty house ground would give that symptom
You can use your volt meter

Appie eleganza 76 "Olga" now sadly sold 6 wheel discbrake Quadrabags Springfield stage 2 462 olds Manny tranny ( pictures at http://www.gmcmhphotos.com/photos/g6489-olga.html Fulltiming in Europe july 2014 til july 2016 Denmark

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Re: [GMCnet] shore power... shock! [message #250120 is a reply to message #250114]

Mon, 19 May 2014 14:34

Dennis S

Messages: 3046
Registered: November 2005

Karma: 2

Senior Member

Check Ken Burtons tech article on grounding. It explains shock from wrong grounding.

Also see the article by Bob Hendrickson.

http://www.gmceast.com/technical/

Dennis

Ek_Lektro wrote on Mon, 19 May 2014 12:17

Well, Here's a head-scratcher for ya...
And despite my "Eklektro" email handle, I'm not formally schooled in 110v electrical, so any advice appreciated! (and if this problem wasn't so intermittent, then maybe i would've solved it by now)

Sometimes when i'm plugged into shore power, i'll get a shock by touching most metal
parts on the RV (door handle, bumper, alcoa wheels, etc). I measured it with the voltmeter (with positive lead on the metal and negative buried into driveway dirt), and its fluctuating between 30 to 60 volts, AC... enough to raise your hair a bit!
The problem never happens when i'm inverting 110 volts,
(and maybe its a coincidence, but it seems to be more prevalent when the driveway is a little wet).

Here are a few possibilities / wild guesses...
- possible fault with the grounding at my garage's 110 volt service? I know that my landlord had done some re-wiring a while back...
- possible fault with the extension cord (i'll see if i can get another heavy 50 footer, to test it out)
- possible incorrect wiring when my old Onan bit the dust, and i recently had a Generac put in,
wired to the same original heavy-duty outlet
And yes... The main problem is that I can't seem to get it to consistently misbehave...

OK, thanks much for any insights,
Greg / Los Angeles / 78' Eleganza II (and '76 Birchhaven 21-foot custom cut-down)
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Dennis S
73 Painted Desert 230
Memphis TN Metro

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Re: [GMCnet] shore power... shock! [message #250129 is a reply to message #250114]

Mon, 19 May 2014 15:49

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

The green wire safety ground has one purpose in the coach electrical system It is to assure that the body of the coach is alway grounded and that what you are experiencing does not happen. You are getting shocked because the frame / body of the coach is not at the same potential as the earth you are standing on.

You will not get shocked when running on the Onan or an inverter because these items have no connection to earth ground like commercial power does. So trouble shoot the green wire ground from the body to the ground connection on the commercial power to find your problem.

First test the receiptical you are plugged in to and see if it is wired correctly. If you do not know how to do it with a meter, then buy a circuit test from Menards, Home Depot, Lowes or Walmart.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: [GMCnet] shore power... shock! [message #250130 is a reply to message #250114]

Mon, 19 May 2014 15:54

lqqkatjon

Messages: 2324
Registered: October 2010
Location: St. Cloud, MN

Karma: 5

Senior Member

I had the same issue, only noticed it when I had my knee in the dirt and was working on frame. I found a pretty ugly looking receptical. and that took care of that. But my coach still popped GFI. so I had more work to do.

so I would go through and check all recepts (easy to pull out and look at them, my palm beach only had 5 I think). make sure they are all not burnt, wet, or corroded.

I just went through this yesterday to find that gfi issue: with power off/unplugged/not inverted, you can check resistance between the neutral and ground.

I had to pull each neutral out of the bar in the electrical panel on the coach, and I was able to find one that was showing some resistance between it and ground. (should be open with all things off). it traced it to rear a/C. I wire nutted it off(A/C disconnected). and I no longer pop the gfi. I have yet to go deeper into the A/C for the problem.

it is just a guess. but I am guessing you are getting a neutral to ground issue. rather then a hot lead to ground.

Jon Roche 75 palm beach EBL EFI, manny headers, Micro Level, rebuilt most of coach now. St. Cloud, MN http://lqqkatjon.blogspot.com/

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Re: [GMCnet] shore power... shock! [message #250134 is a reply to message #250130]

Mon, 19 May 2014 16:28

emerystora

Messages: 4442
Registered: January 2004

Karma: 13

Senior Member

The gfi is often tripped through the electric water heater in the GMC motor homes.
You might test it again when the water heater is on and calling for heat (the thermostat on trying to heat the water ).
Emery Stora

> On May 19, 2014, at 2:54 PM, Jon Roche wrote:
>
> I had the same issue, only noticed it when I had my knee in the dirt and was working on frame. I found a pretty ugly looking receptical. and that
> took care of that. But my coach still popped GFI. so I had more work to do.
>
> so I would go through and check all recepts (easy to pull out and look at them, my palm beach only had 5 I think). make sure they are all not burnt,
> wet, or corroded.
>
> I just went through this yesterday to find that gfi issue: with power off/unplugged/not inverted, you can check resistance between the neutral and
> ground.
>
> I had to pull each neutral out of the bar in the electrical panel on the coach, and I was able to find one that was showing some resistance between
> it and ground. (should be open with all things off). it traced it to rear a/C. I wire nutted it off(A/C disconnected). and I no longer pop the
> gfi. I have yet to go deeper into the A/C for the problem.
>
> it is just a guess. but I am guessing you are getting a neutral to ground issue. rather then a hot lead to ground.
>
>
>
> --
> 75 palm beach
> St. Cloud, MN
> http://lqqkatjon.blogspot.com/
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Re: [GMCnet] shore power... shock! [message #250138 is a reply to message #250114]

Mon, 19 May 2014 16:53

Messages: 1262
Registered: September 2009

Karma: 0

Senior Member

We had the same problem, and it was due to three things: one, the outlet
we were plugging into had a reversed hot and neutral. Get a cheap outlet tester
from any hardware store to make sure the outlet is wired correctly. It's a good thing to
carry in the coach to test campground outlets.

Two, a wire had worn through and was making contact with the frame.
I could see this resulting in intermittent problems. see:
http://www.gmcmhphotos.com/photos/member-galleries/p41713-original-bad-wiring-de.html

Three, the previous owner had rewired the coach electrical panel incorrectly.
The neutral and ground wires should NOT be bonded together in the coach.
The coach electrical is considered a sub-panel by code standards. Neutral and
ground should only be bonded together at main panels.

Karen
1973 23'
1975 26'

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Re: [GMCnet] shore power... shock! [message #250140 is a reply to message #250138]

Mon, 19 May 2014 17:14

tphipps

Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL

Karma: 9

Senior Member

I use one of the three neon lights plug-in devices to test my connections to shore power whenever I plug in. I just leave it in my outlet near the power panel. It also makes a nice night light, since it is in the bath on my Avion model.
Tom, MS II

2012 Phoenix Cruiser model 2552 KA4CSG

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Re: [GMCnet] shore power... shock! [message #250166 is a reply to message #250114]

Mon, 19 May 2014 22:48

Ek_Lektro

Messages: 167
Registered: March 2011

Karma: 2

Senior Member

That's great Dennis, thanks;
Nice documentation from Ken...
I was not aware that 12 volt house connections should be grounded to the aluminum chassis
and NOT the steel frame. The PO had the house batteries ground connected to the steel frame (and other mechanics over the years also used the steel frame)... hmmm....
I'm gonna do some more reading and check some things out before i'd post any further questions...
Thanks again,
Greg

> Check Ken Burtons tech article on grounding. It explains shock from wrong grounding.
> Also see the article by Bob Hendrickson.
> http://www.gmceast.com/technical/
>
> Dennis

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Re: [GMCnet] shore power... shock! [message #250172 is a reply to message #250114]

Mon, 19 May 2014 23:19

Jerry Sitzlar

Messages: 206
Registered: February 2013
Location: Lenoir City, TN

Karma: 4

Senior Member

My third wag for the night. If you're reading up to 60 volts across ground (half a swing on the cycle or hertz) while on shore power and there was recent wiring done on the garage/house, I would put money on that wiring not correct. I would get one of the 3-neon testers that Tom Phipps was talking about and check out both the coach and house. They are pretty cheap at most box or hardware stores. I have one each in the coach and house. Check the coach while on genset power since the Onan was also replaced, and the house.

Jerry Sitzlar..... 77 Eleganza II, Twin bed, dry bath...... Lenoir City, TN (near Knoxville)

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Re: [GMCnet] shore power... shock! [message #250175 is a reply to message #250172]

Tue, 20 May 2014 03:44

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Greg,

You are partially correct some vehicles do use the frame as the master ground. In out case we have two separate 12 volt systems. Anything powered by the engine driven alternator (and starting battery) uses the engine block as the master ground. Everything else 12 volt powered by the converter and house battery(s) uses the aluminum body frame as the master ground. So when attaching any 12 volt device you want to attach it as close to the master ground as possible.

There are cross connections (jumper straps) between the two master grounds and the frame. As long as those straps and their connections are in good condition, things will work when not attached to the proper ground location. Using those ground routes adds to the length of the return path to the master ground. Over the years those straps do deteriorate.

As a side note, I had a recent electrical failure on my Chevrolet Colorado. One of my trailers that I tow has a winch on it. The winch would not run due to low voltage. Also the LED trailer lights quit. It took me a while to find the problem. It was that the after market heavy duty trailer 7 pin wiring harness used the truck frame as ground. It turns out that the Colorado has no permanent electrical connection between the body (or engine) and the frame. BTW, the truck bed also had no connection to master ground but the body did. The solution to this problem was to either run a heavy gage wire from the master ground (engine) or add a jumper from the body to the frame. The body is already grounded by GM with a 2 ga. cable. I did the last since it was the easiest and quickest for me to do. So here is another case where the frame is not used as a ground return path.

Over the years there have been many strange failures where those ground jumpers to the frame failed. GM had problem with shift cables on Cameros and Firebirds burning up shift cables. The problem was jumper straps deteriorating or being left disconnected. The ground current would then travel along the parallel ground path through the shift cable which could not handle the current.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: [GMCnet] shore power... shock! [message #250181 is a reply to message #250114]

Tue, 20 May 2014 07:51

bwevers

Messages: 597
Registered: October 2010
Location: San Jose

Karma: 5

Senior Member

I'm going to post another theory. Maybe your house has bad wiring and the neutral on the house panel. has pulled loose and the house gnd is the return path. If your coach is plugged into a GFI it should trip.
regards

Bill Wevers GMC49ers, GMC Western States 1975 Glenbrook - Manny Powerdrive, OneTon 455 F Block, G heads San Jose

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Re: [GMCnet] shore power... shock! [message #250194 is a reply to message #250181]

Tue, 20 May 2014 13:30

appie

Messages: 902
Registered: April 2013
Location: denmark

Karma: 2

Senior Member

I had the same problem with Olga As it worked out I had a loose ground connection in the house

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