On our trip at the end of last month, a table lamp quit working. Changing the bulb did not help, but a voltage detector showed voltage present at the base of the socket. I figured the switch in the lamp socket died.I finally got around to buying a new lamp socket and I installed it today. No joy.Using an outlet tester on the receptacle showed hot and ground reversed! I checked the breaker panel, and things were wired correctly on that end of the circuit. Some other outlets on that circuit checked out okay so I began to work upstream from the problem.Long story short, I found the circuit routed through a GFCI outlet in the basement. That GFCI outlet and everything downstream tested “hot and ground reversed.” I pulled the line side of that outlet and found that the power coming in was correct, black = hot, white = neutral, bare = ground. The GFCI outlet was wired correctly, line side and load side. The problem has to be in the GFCI outlet.After removing the GFCI outlet and connecting the appropriate wires with Scotch locks / wire nuts, everything downstream works okay.The GFCI outlet does not seem to want to reset. I will replace it. Also, I think I will re-route some wiring so that the interior outlets that are not near water, etc., are not routed through the GFCI receptacle, as I see no need for that kind of protection.My question: I expected that if the GFCI outlet tripped, it would “interrupt” the circuit, i.e., break it. Could it have shunted the hot to ground, thereby activating the ground wires downstream, yet leaving the hot wire dead downstream? I Googled to see how the GFCI outlets work, but came up empty.Wayne

No it wont re-route the power - it probably just went bad.I would not change anything to negate it's effect to outlets down the line. It doesn't hurt anything to be protected.

i just ran into this on a heartland bighorn it was the wiring in a junction had wrong size wirenuts and the hot was laying acrooss the ground. It was not pretty at the melted nuts and wiring

Wayne,Indeed, replace the offending GFI. They DO fail.Your wiring "around it" showed that the wiring was OK.

ScottG – In this case, it did reroute the power. At the downstream receptacle, a voltage detector showed ~120 volts between ground and neutral, with ground being hot. That is what puzzles me. I would never have expected the GFCI to have failed in that manner.The only problem with having the downstream outlets protected is that the ground wires became hot. And it took me quite a bit of time to discover that the voltage I was detecting was in the ground wire, not the hot (black) wire. I wish I understood why the GFCI outlet failed this way.Newman – In my case, I had no mis-wiring; the GFCI just did something I never would have expected.Brett – Having bought a 17-year-old coach, I expect little problems from time to time, and solving them will help keep the brain cells working. A $15 dollar part is not a big deal. I’m just hoping to learn something from the experience. :)Wayne

Something is not right here. The ground does NOT pass THROUGH the GFCI and hence it cannot have 120V from the GFCI or elsewhere unless it's open or a ground could be connected to 120V somewhere but a properly wired GFCI does NOT pass the ground through and a correctly wired ground coming into a GFCI will be "earth ground" and not be at 120V. A GFCI does have a ground connection for the ground lug and modern GFCI's can also detect a neutral to ground fault. A GFCI does pass through the hot and neutral and in fact detects a current difference between these two wires. Perhaps there is a wiring problem upstream or the wiring colors are misleading vs actual connections or ???

Chasing electrical gremlins - GFCI outlet puzzle

CA_Traveler
Explorer III
Nov 22, 2014
Everything you described suggests a higher resistance short which would not trip the CB vs a direct short. Voltmeters, testers, etc typically draw so little current that the results can be misleading but testing with a load will often show different results.
Empty_Nest__Soo
Explorer
Nov 22, 2014
After checking everything else on that circuit, I decided to take a look inside the GFCI outlet.

There was black residue inside the GFCI outlet. Some of the electronics on the little printed circuit had fried. It did not trip, it failed.

I can only conclude that the GFCI outlet failed in such a way that it activated the ground when it failed.

One thing I haven’t quite figured is, if this shorted to ground, and assuming a good ground to earth, why did the breaker not trip? Perhaps it could pass very little current, not enough to trip the breaker.

At this point, I will replace the GFCI outlet and call it good.

Wayne
Wayne_Dohnal
Explorer
Nov 22, 2014
I'll jump on the bandwagon of saying there's more to this than meets the eye. The way the GFCI outlets are mass produced as identical devices, I think the odds of one being able to reverse the hot and ground are astronomical. Coupled with the previous observation that the ground goes 'to', rather than 'through' the outlet, the odds are astronomical-squared.

The outlet tester gives a possible interpretation of the pattern of lights, not a definitive answer. With 2 lights lit in the 'hot-ground reversed' pattern, it's indicating voltage between ground-neutral and ground-hot. Another cause of this indication would be 'neutral connected to hot', which I believe would be consistent with your measurements and observations. While I still find it unlikely that the outlet would do this, the odds are IMO somewhat less than astronomical. There are probably other causes of the outlet tester's indication, too.
myredracer
Explorer II
Nov 22, 2014
I too would want to know what caused that.

I would think the very first thing you want to make certain of is that the ground inside your MH isn't at 120 volts to earth (as at ground point in your house panel or pedestal) otherwise you'd have a hot skin which is dangerous. Use a non-contact voltage tester to determine that. Google "No-shock Zone".

It's hard to diagnose something like this without being there, but some other thoughts:

Once you know the shore power recept. you're plugged into isn't mis-wired, you might try using the ground bus behind the converter panel as the ground reference point and use a long wire to get to your voltmeter to test hot, neutral and ground to the ground reference point at various receptacles throughout the MH.

Maybe you could also measure resistance between H, N & G in receptacles and at the panel? With shore power disconnected of course. You should have full continuity between the panel and H, N & G in all farthest recept. branch circuits.

If the table lamp is intermittent, that could indicate a faulty connection somewhere. Intermittent connections can be difficult to find. You may want to pull out every receptacle in that branch circuit and inspect the terminations as well as at the panel.

If you have an open wire somewhere, a voltage tester or high impedance voltmeter can give you a false reading. Or a tester or voltmeter may show a circuit is okay with no load, but a bad connection won't support a load.

Not sure if these will help, but have a look anyway.
The circuit detective
Home Improvement help

In this Youtube vid a master electrician says not to trust a plug in tester if it says hot and ground reversed.
CA_Traveler
Explorer III
Nov 22, 2014
YC1 has an excellent point. Also instead of using the circuit wires use a separate wire connected to the frame which should be bonded to the pedestal ground wire through the rigs CB panel.

And at 11 degrees I'd wait for it to warm up a bit. :D
YC_1
Nomad
Nov 22, 2014
Your digital voltmeter was measuring a minute amount of current, enough to make the meter run but not enough to run a light bulb.

With the GFCI bad there could be internal carbon traces or even a high valued resistor that does some sensing that is now feeding back power.

If you had left the light in the ON position there would have been a load on the line and your measurement would have been zero volts.

To demonstrate my theory, put the meter in the DC volts position and go to one of your 12 volt batteries. You could do this with a flashlight battery too.

Place one of the negative leads of the probe on one post of the battery. Now with one hand pinch the other lead. With your free hand, touch the other post of the battery. By pinching harder or wetting your fingers you will get the full battery voltage showing. I promise you there will be no shock or any sensation at all.
CA_Traveler
Explorer III
Nov 22, 2014
Perhaps it was miswired when you bought it and then the GFCI failed which caused the light problem.
Dusty_R
Explorer
Nov 22, 2014
Hot and ground reversed, or hot and neutral reversed.
Empty_Nest__Soo
Explorer
Nov 22, 2014
CA Traveler wrote:
Something is not right here. The ground does NOT pass THROUGH the GFCI and hence it cannot have 120V from the GFCI or elsewhere unless it's open or a ground could be connected to 120V somewhere but a properly wired GFCI does NOT pass the ground through and a correctly wired ground coming into a GFCI will be "earth ground" and not be at 120V.

. . .

That’s pretty much the way I had it figured. Rather than simply replacing the GFCI outlet and calling it good, I would like to figure out how I came to have the situation I had so I can be sure it is corrected. Since failure of the GFCI outlet apparently does not explain the problem, I will keep looking. I will replace the questionable GFCI outlet in any event.

The GFCI outlet and all others down the line from it tested “hot and ground reversed.” The ones up the line tested okay. Removing the GFCI outlet from the circuit seems to have made things right. I did not see any evidence of arcing around any of the wires. But the light that was plugged-in down the line from the GFCI outlet worked before, then quit without explanation. I’ve had this coach only a few months, and I cannot recall that I have yet had any other load anywhere else on the 3 outlets down the line.

Before removing the GFCI outlet, I removed the next outlet down the line. Checking bare wires with a digital multi-meter, I found nothing between black and white. I found 120 volts between bare and white, with bare being the hot side. That is consistent with the results from plugging in the outlet circuit tester.

I quit working outside last evening when it got too dark and cold. I did not re-check everything before and after the box where the GFCI outlet was removed. But a test light plugged in down the line worked after the GFCI outlet was bypassed, but not before. I will go back out and check some more when it warms up some. Currently, it is 11* outside.

Wayne
CA_Traveler
Explorer III
Nov 22, 2014
Something is not right here. The ground does NOT pass THROUGH the GFCI and hence it cannot have 120V from the GFCI or elsewhere unless it's open or a ground could be connected to 120V somewhere but a properly wired GFCI does NOT pass the ground through and a correctly wired ground coming into a GFCI will be "earth ground" and not be at 120V.

A GFCI does have a ground connection for the ground lug and modern GFCI's can also detect a neutral to ground fault. A GFCI does pass through the hot and neutral and in fact detects a current difference between these two wires. Perhaps there is a wiring problem upstream or the wiring colors are misleading vs actual connections or ???

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