Electrical issue (AC Power)

[Racer-X-]

I'm doing some repair/restoration work on a 1995 Fleetwood Flair (built on a 1993 Chevrolet P30 chassis). I'm pretty good with the mechanics of the chassis, engine, transmission, suspension, the "motor" part. The "home" part is foreign to me.

One issue I've discovered (the hard way) is that there's something seriously wrong with the AC wiring in this one. We have it plugged in to an outdoor outlet on his house (GFCI protected). The RV has a 30 amp plug on it, but we've got an adapter to a "normal' three prong, 12 Gauge extension cord for now.  We're not running the AC in the unit or anything significant. We haven't even turned on the fridge yet. Mostly, just a "boom box" to listen to while we're cleaning up and dealing with various issues.

Here's the first major issue.  When I'm working on the thing, the frame and chassis are live with AC power. If it's plugged in, and I'm kneeling on the ground and I touch anything metal on the frame, engine, suspension, whatever, I get a serious shock, like I stuck a paper clip in an electric outlet. There's no issue if I'm working through the doghouse from inside to work on the top of the engine. The issue is only when I'm on the ground and touch the thing with my bare hands or with a metal tool/wrench. If I unplug the power, there's no issue. Actually, working on the thing with it plugged in is borderline dangerous.

I checked the AC outlets in the RV with one of those plug in analyzers (something like https://amzn.com/B00170KUPC ) and it's reading "Hot/Neutral Reversed" for all the outlets in the RV.

I don't even know where to start to diagnose and fix this. Is there any obvious place where something could be connected incorrectly to cause this problem?

 

[Gary RV_Wizard]

Sounds like a couple problems. The reversed polarity could be as simple as a faulty adapter where you plug to the house outlet,  or even that outlet itself is reversed. Neither, though, would cause the chassis to be hot.

The hot chassis would be caused by some wire shorted to ground, either a neutral or a hot. Could be anywhere, but I'd start by turning off the all breakers in the load center to see if that stops it. If it does, turn breakers back on one at a time to see what circuit makes the short re-appear. Then start checking that circuit for wiring problems.  If turning all the breakers off does not remove the stray power from the chassis, then the short must be where the shore cord enters the coach and then connects to the load center main breaker.  If the coach has an auto-transfer switch that sifts the power soruce from shore cord to the generator, that's in the wiring path also and could be where a wire is touching the chassis.

The chassis should not be hot ever, but it is part of the ground system in the RV.  Both the 120v ground wire and the 12v negative are connected to the chassis.  However, it is supposed to be tied to the ground where the shore power cord plugs in rather than sending stray current thru your body when you touch it and earth. Therefore you also have an open ground to the shore power cord, or possibly no ground at that outlet you are using. Try your outlet tester in that for starters. If the ground is good there, once again check the adapter for a proper grounding connection, and also the shore cord for same.

 

[Harvard]

First off, you have an OPEN GROUND conductor OTHERWISE the CHASSIS would not be HOT.

Second, an OPEN GROUND conductor leaves the CHASSIS to float and does not need any direct short from HOT to CHASSIS to be 110/2 = 55 VAC or less.
This is due to stray capacitance which in turn conducts a small amount of AC current BUT not enough to trip GFIs.

 

[John From Detroit]

Not on a motor home but my expierence
1st Trailer was a PUP. no real electrical system (just one outlet with a plug outside) I added more myself done properly

2nd was a SCAMP TT this was the first trailer with a real power INLET and electrical system.. Alas the prior owner had made up his own adapter and he's swapped the black and white wires.. YES I got "Bit" several times.. Ground was good but Id' still get BIT inside the trailer.. I fixed it.

As others have said if you are getting bit RV to Feet on ground you likely have an open ground

There is a device called a 3-light outlet tester. Any hardware. Wal*mart. RV dealer.  (Truck Stops. some gas stations. Many supermarkets, I mean you can get these things all over creation)

Plug one in and see what lights.  RED lights (generally) are an indication of power  Two Green is good .

 

[boatbuilder]

Start at the outlet on the house first. Put a meter from the wide slot(neutral) to the ground socket. You should have no voltage. If you have 110V then you have reversed polarity. Fix that before anything else. If the house outlet is good, plug in the coach and check an outlet on the coach the same way.

 

[FunSteak]

I recommend you read Mike Sokol's articles on this on his site, "No Shock Zone".  You may have a "reverse polarity bootleg ground" in the receptacle into which you're plugging your coach.  This is NOT testable with a three-light tester, and results in exactly the situation you're experiencing. 

These articles will get you started: 

http://noshockzone.org/are-little-shocks-ok/
http://www.rvdoctor.com/2001/07/friends-of-gary-mike.html

This is a diagram of what's happening in this circumstance:  http://2.bp.blogspot.com/-zwUmy575iQA/T_i73zMuhRI/AAAAAAAABZA/jufx1Ja7eC4/s400/Bootleg+Ground+Demo+large.jpg

You have a potentially very dangerous situation here.  I strongly recommend you check for the RPBG condition ASAP. 

 

[Racer-X-]

Thank you to everyone for the replies.

At this point, I'm fairly certain the hot/neutral swap is at one end or the other of the "shore power" cord. When I get back over to work on this one some more, that's the first place I'll be checking. I'm wondering it the ground is disconnected there as well.

I'm fairly confident of the house wiring where I'm plugged in. There were some issues in that house, but I had an electrician over there to resolve all that about 5 years ago. It should all be correct to code and properly functioning now, including the GFCI outlets outside.

Floating ground on the chassis and capacitive coupling could explain the "hot chassis."  Or I might have a short from a neutral (now hot) to ground. After I get the polarity issue checked, I'll check from ground to the chassis with a meter and start turning off circuits if I find voltage there.

 

[Harvard]

These 15A/30A "hockey puck" adaptors can be the source of an open ground conductor.
The 30A female GND does not make connection to the 30A male GND.
Notice how I crimped the 30A female GND so it would mate with the 30A male GND.