Stray voltage - electrocution

[Rob Hentges]

In the process of replacing my water heater, I felt myself getting shocked when sitting on my lawn and touching metal parts of the RV. I put a meter in it and discovered 70 volts AC. I fixed this by hammering a ground rod into the ground and attaching a wire from the rod to a metal part on the chassis. I haven't done any troubleshooting yet. I want to see if I get the same stray voltage under generator power as I am seeing when plugged into the household electric. Any ideas? Everything is working fine.

[cb1000rider]

Rob, I don't have any ideas, but I noticed a "tingle" when working under a new Keystone and touching a sweaty arm to it.. Need to check mine too.. Lots of "grounds" on these things that all track to the frame. Could try shutting down breakers 1 at a time to see if that changes things.

[cb1000rider]

Read this:
RV Electrical Safety: Part IV – Hot Skin | No~Shock~Zone

Apparently it's called "hot skin" and is pretty common. Could even be what you've got it plugged into...

[dpinvidic]

The Green wire in your shore power cord is connected to Earth Ground.
It IS actually a rod in the ground, usually near the electric meter or breaker panel.

In your coach, the green is connected to the metal chassis and most other metal parts.
If you feel a shock, there is a fault somewhere in this electrical path(open connection)
Could be on the shore power side, or on the coach side.

This is a must fix problem.

Dan

[wa8yxm]

RV's should be connected to shore power by a 3 or 4 wire connection..
On a 30 amp RV you have a hot wire, a neutral and a safety ground.

What happens if you have an open ground?

Well your ROMEX cables consist of 3 wires, parallel to each other and insulated from each other arrainged like this |||

Let's take a look at just the first two.

Two metal objects seperated by insulation = A Capacitor.
A Capacitor to AC looks a lot like a resistor

Now let's look at the right two.. Same as the left two

So we have a capacitive voltage divider...

Yup that is what it is. and given the yards and yards of wire,, I fairly big one.

NOW; normally the neutral is bonded to ground, but now it's not So the safety ground wire (The one in the middle) takes on 1/2 the line voltage.. More or less depending on other things that affect it.

If you unplug from shore and run generator you should NOT see this as there is no path to ground.. But it's still there.

[nothermark]

You should already have a chassis connection to ground via the green wire in your shore cable. You might want to find out why that is not working.

[Rob Hentges]

Originally Posted by nothermark

You should already have a chassis connection to ground via the green wire in your shore cable. You might want to find out why that is not working.

Yeah, I'll have to dig a little deeper. I recall a previous motorhome also giving me the tinglies if I touched it in the rain. It was plugged into the same outlet. I have recently replaced that outlet, and know that the ground wire is connected at the outlet. What I don't know, is whether the ground wire is actually attached to ground somewhere. It is not the only outlet on the circuit.
The 8ft ground rod took the voltage to a level below 1 volt, so I made it safe. I realize I still need to find the reason. I'm considering adding another 8ft ground rod near the outlet and hard wiring the rod to the ground connection in the outlet. Any reason I shouldn't do this?

[Gary RVRoamer]

According to the electrical code, you should not have multiple grounds in any system, and your house is all one power system. It's ground point is usually where the service entrance connects to the house. That's why your coach does not bond neutral and ground onboard - that bonding is only allowed at the main power panel for the system. Yeah, there are a few exceptions to these rules, but they don't apply here.

So no, you should not add a separate ground rod at the power outlet. Perhaps some NEC guru will attempt to explain why, but it's pretty complex stuff for this audience.

There really is no need if the outlet is properly wired, i.e. has its own ground wire back to its power source.

[Rob Hentges]

Originally Posted by Gary RVRoamer

According to the electrical code, you should not have multiple grounds in any system, and your house is all one power system. It's ground point is usually where the service entrance connects to the house. That's why your coach does not bond neutral and ground onboard - that bonding is only allowed at the main power panel for the system. Yeah, there are a few exceptions to these rules, but they don't apply here.

So no, you should not add a separate ground rod at the power outlet. Perhaps some NEC guru will attempt to explain why, but it's pretty complex stuff for this audience.

There really is no need if the outlet is properly wired, i.e. has its own ground wire back to its power source.

I'm an engineer with 25yrs experience and a degree in physics, so could probably understand if I took the time to study it. I know enough about electricity to be dangerous. There are a few certified electricians where I work, so I'll run this problem by them also. I recall about 15 yrs ago when I installed my pool that I was required to add a ground rod and attach it to the pool motor.

[KIX]

Not to muddy the waters here but a question.
If he is connected to a 4 wire / 50 amp receptacle could a loose or broken neutral allow the symptoms the OP has?

[cb1000rider]

Originally Posted by KIX

Not to muddy the waters here but a question.
If he is connected to a 4 wire / 50 amp receptacle could a loose or broken neutral allow the symptoms the OP has?

No, I don't think so. I broken neutral would mean that the 120v "legs" are unusable. It'd mean you have 240v or nothing.

[cb1000rider]

Originally Posted by Rob Hentges

I'm an engineer with 25yrs experience and a degree in physics, so could probably understand if I took the time to study it. I know enough about electricity to be dangerous. There are a few certified electricians where I work, so I'll run this problem by them also. I recall about 15 yrs ago when I installed my pool that I was required to add a ground rod and attach it to the pool motor.

Rob, if you have an older home, there may be conditions where additional grounds are warranted or desired, but without knowing the specifics and your particular code, probably best not to give you incorrect advice.

In terms of understanding it, it's pretty simple. Something is using you for a ground wire, preferring the "Rob" path to a proper ground. It absolutely could be the outlet - something as simple as a poor connection somewhere up stream from that outlet.. Or it could be an individual appliance that is behaving badly.

If you have a volt meter, see if you can measure it. And determine if it's the outlet, RV, or perhaps the cable in between.

[Rob Hentges]

I'll check the outlet ground tomorrow and report back. Thinking that's it because my previous RV also gave me tinglies. With no added grounds, I meAsured 70 volts from chassis to dirt. I did a quick thing where I put a tent nail in the ground about 8 inches and connected to chassis with wire. That brought voltage down to 20. Today I sunk a grounding rod 8ft deep and connected that to chassis. Voltage dropped to below 1. Once upon a time the outlet was a gfi. I got tired of it tripping when powering things with electric motors so I replaced it with non gfi. It is on porch, under soffet so it doesn't get wet. I know that the outlet inside my house in the same vicinity is on the same breaker. Maybe someone didn't hook a ground wire to that one, which would make the outside outlet effectively ungrounded.

[nothermark]

The typical house is wired with neutral and safety ground separate until they get to the main panel. At the main panel they are connected together and connected to a ground rod. Usually the ground rod is just below the service entrance. If that ground connection gets broken everything will work but strange things like 70 V to ground can happen. I'd be looking at that connection. YMMV.

What is interesting is that trailer wiring calls for a ground at the post. What I am not sure is whether that means a separate ground rod or a run to the combined neutral and ground at a central point.

The reason for the separate ground and neutral connections is that ground is an open circuit. Only half the connection to supply current. Any insulation failure will close the circuit thus putting current in the ground leg. As a safety device the wire is a lot lower resistance than the average human so they might get a tingle instead of fried. It also permits sensing ground currents to shut down the system for safety.