Shocking! AC power tingle between frame and (real) ground

[joebedford]

I was doing something at the back of my RV today and I put one knee down into fairly damp earth (heavy rains here the other day). I steadied myself by leaning my right forearm on the bare aluminum hinges of my ramp. I didn't exactly get a 'belt' but I definitely got a strong tingling.

What's up with that? Is it dangerous?

For the record, our 5er is a 50A rig plugged into a 50/30 dogbone with a 30A extension plugged into a 30/15 adapter plugged into a regular household outlet (not GFCI).

[Wayne_Dohnal]

Had the same issue a couple of years ago.....but the cause for me was the 120v heating unit on my water heater. Evidently, this causes this problem on a regular basis. If you have a gas/electric water heater, it's worth checking out ad easily fixed.

A fault in the water heater cannot cause a non-hazardous tingle between an RV and earth ground. The only thing indicated by a non-hazardous tingle is an ungrounded RV chassis. A water heater fault combined with an ungrounded chassis creates a very hazardous situation, which is why a good ground connection is so important. The water heater fault will however cause a shore power GFCI to trip when the chassis is properly grounded.

If you have a "hot" chassis there's a grounding problem. There may or may not be an additional problem on top of that.

[Wayne_Dohnal]

My understanding of the NEC is that neutral and ground NEVER get bonded at subpanels, that's why you don't do it in an RV, it's basically a sub panel.

That's true now, wasn't in the not-too-distant past for detached buildings. According to this forum thread 3-wire feeds to existing detached buildings the change occurred at the 2005 NEC to 2008 NEC transition. Haven't researched it myself.

[BurbMan]

Well, I guess the NEC doesn't apply in Mehico, senor.

[MEXICOWANDERER]

Except when it isn't due to a faulty campground nightmare electrical system. One single stupid bootstrap ground screws the whole system up and no tester will ever find it. I would LOVE for someone to explain to me how a 60 amp rated rig chassis to earth ground security wire would jeopardize someone.

Too many "Oh holy cow, I'm sorry about that, we'll fix that right away" to suit me. This isn't a light bulb out or a dripping faucet issue.

The NEC ASSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSumes the campground electrical is code compliant. Saint Peter assumes nothing.

[BurbMan]

Wayne Dohnal wrote:
I have an outbuilding that's fed from the main panel in the house but has its own independent grounding electrode. There's a neutral-ground bond at the main service entrance, and another at the outbuilding.

My understanding of the NEC is that neutral and ground NEVER get bonded at subpanels, that's why you don't do it in an RV, it's basically a sub panel.

[UConnrick]

Had the same issue a couple of years ago. I'm not on the same level of understanding as some on here but the cause for me was the 120v heating unit on my water heater. Evidently, this causes this problem on a regular basis. If you have a gas/electric water heater, it's worth checking out ad easily fixed.

Good luck.

[MEXICOWANDERER]

Potential between an exposed surface insulated from earth ground may instead decide to travel through a person's body. Is there any other issue here? This is why I physically BOND the trailer to earth ground. Every time. Hypothesis, Assumption and Supposition are eliminated out of the equation. 100.000000000% of the time. Many of you are not susceptible to life-threatening cardiac arrhythmia. I can not afford to play games. Offered As My Most humble Opinion.

[Harvard]

MPD56 wrote:
Harvard: There are lots of what if here. The diagram in your last post although could work, it is probably not the way the Power Company has connected it physically. If you have a voltage drop that can be read with a meter, then you will get current flow through a resistive and/or impedance electrical path.
If an over head bare high voltage power line had broke and is lying on the ground, you can’t assume the earth is a pure conductor (0 resistances to current flow). This is the reason why grounding and bonding methods are so important. The powers that make the Electrical Codes can’t make it 100% safe.

The OP trailer could have a bonding or grounding problem that is causing him to feel a shock. I say “could” because what if the wet ground was providing the 18 volts from the power cord sitting in the water and the chassis of his trailer is a less resistance path to the source’s safety ground, meaning his trailer chassis is wired properly? At some time or another you’re going to read a voltage from chassis to earth ground, the code’s wiring methods are there to hopefully reduce that voltage so the no harm comes to us. From a keyboard, I can’t assume were the OP’s problem is, but he knows he had a problem and is taking steps to correct it.

FYI:
The power company use meters to detect ground fault currents and they are not volt meters from a hardware store. A GFI receptacle doesn’t monitor voltage to ground. 18 volts I wouldn’t think a human would feel a strong tingle, at least I don’t? There is a good reason why the power’s to be picked no more then 120 volts to ground and not a subject that can be taught on a RV Forum.

Yes, I agree fully that my circuit does NOT reflect the applied "Circuit Geometry" but I thought it would be close enough for a 60 hertz discussion (and not to forget about the "fail safe" aspects of the real wiring). Thanks for the input. By the way, who is this Eddy guy anyway? He is probably a cousin of Mex. :B

[Harvard]

MEXICOWANDERER wrote:
Eddy currents.

What is your objective?

My objective is to be as smart as Mex! 🙂

The OP had 18 VAC at the campground and 2.2 VAC when he got home. My thought was 2.2 VAC seems high so I started to look at my RV at 0.4 VAC and found this "Earth Current". I talked to Eddy (ARRL Handbook) and he says yeh it is probably his current. Thanks Mex for helping us all be smarter.

[kampinguru]

Harvard wrote:
For sure you have an open ground conductor. In other words, there is no continuity in the ground wire from the RV chassis to the power distribution Earth Grounding Rod. Be very suspicious of the "adaptors".

I would look here as well. I have the same problem when I plug my trailer into the house 110 socket using the dogbone converter. Not a problem any other time, only when using the dogbone. I also get it when I am using my generator to power the trailer due to no ground on the genny.

[MPD56]

Harvard: There are lots of what if here. The diagram in your last post although could work, it is probably not the way the Power Company has connected it physically. If you have a voltage drop that can be read with a meter, then you will get current flow through a resistive and/or impedance electrical path.
If an over head bare high voltage power line had broke and is lying on the ground, you can’t assume the earth is a pure conductor (0 resistances to current flow). This is the reason why grounding and bonding methods are so important. The powers that make the Electrical Codes can’t make it 100% safe.

The OP trailer could have a bonding or grounding problem that is causing him to feel a shock. I say “could” because what if the wet ground was providing the 18 volts from the power cord sitting in the water and the chassis of his trailer is a less resistance path to the source’s safety ground, meaning his trailer chassis is wired properly? At some time or another you’re going to read a voltage from chassis to earth ground, the code’s wiring methods are there to hopefully reduce that voltage so the no harm comes to us. From a keyboard, I can’t assume were the OP’s problem is, but he knows he had a problem and is taking steps to correct it.

FYI:
The power company use meters to detect ground fault currents and they are not volt meters from a hardware store. A GFI receptacle doesn’t monitor voltage to ground. 18 volts I wouldn’t think a human would feel a strong tingle, at least I don’t? There is a good reason why the power’s to be picked no more then 120 volts to ground and not a subject that can be taught on a RV Forum.

[MEXICOWANDERER]

Eddy currents.

What is your objective?

[Harvard]

Here is a sketch of the Bigger Picture. There is a steady approx 0.4 VAC between the GROUNDS and surrounding EARTH even at the power meter pole.

[Harvard]

BUT, why would the Earth Current NOT take the path of least resistance through the Ground Wire instead of going through Earth? Still puzzled about that! The AC wiring at the Bonding Point and the Ground Rod wire combo may be serving as a small scale step down auto transformer.

EDIT 1:
Just as we have stray capacitance in the RV wiring, we may have stray inductive coupling in the Breaker Box where the N/G Bonding takes place causing a small voltage to develop (ie 0.4 and 2.2 VAC) in the wire to the ground rod..

EDIT 2:
To really get to the bottom of this we would probably need to consider all stray inductance and capacitance all the way to/from and including the Power Transformer on the power pole.

End of story for me.