Hot ground wire and strange voltage readings on multiwire circuit

14 years ago

Hello all,

Let me start off by saying that I'm not an electrician, but I have a working knowledge of home electrical and I can do simple things like change and add recepticles, etc. I know when something is over my head, and I think this is one of them. Just want to get some advice from professionals so I know what to expect when I call in a licensed pro - or maybe it's something simple I didn't think about.

While adding a recepticle above my kitchen counter I figured out, the hard way, that the ground wire was hot. I replaced the existing outlet with a GFI and then installed the new one. I noticed the existing outlet was on the same circuit as the kitchen lights, which consists of two switches, one for a flourescent and the other a hanging light fixture.

The ground wire being hot was strange enough, but then it got stranger. With the GFI switched on, when I turned on the florscent light, only 1/2 the bulbs would come on. If I tripped the GFI the rest would come on and stay one, even when I switched the GFI back on. Also with the GFI switched on I'd get 120V between the ground of both outlets, and the ground from something else, such as the range hood which is grounded. I also got 120V between the outlet grounds and the neutral wires, but 0V between the grounds and the hot wires.

If I switch the GFI off (tripped), I get a strange fraction of voltage from the wires coming into the outlet between the ground and the neutral (e.g. 80V), and between the ground and the hot (e.g. 40V), coincidentally (or not?) adding up to 120.

I opened the light fixture that is on the same circuit to have a look and I believe the circuit comes into this junction box first. At first I noticed that a ground wire and neutral wire slipped right out of the connectors, so I thought that might be my issue. But then I diconnected all the wires here so the downstream receptacles were out of the picture and got similar results as before. But here the ground wire would register 60V between the neutral and the hot.

Strange stuff. I then decided that this was probably over my head. Any ideas?

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Comments (6)

Ron Natalie
14 years ago
You mix "adding" and "replace" in a way that is confusing. You can NOT install countertop receptacles on a circuit that also feeds lighting. Now if your home was old, this wiring is probably grandfathered, but if you are adding a new receptacle you should do it correctly.

How did you determine the ground wire was hot? I actually suspect it is floating which is nearly as bad. All the signs indicate that. I suspect you're using a high impedance meter (good for most things, but it will read stray voltages with one leg connected to a grounded conductor and the other either floating or connected to a long unterminated wire).

A lot of fluorescent fixtures start intermittently without proper grounds. I bet you reach up and touch the fixture or rub the bulb with your hand, the other ones would fire.

I would find all the outlets (lights, receptacles) and any junctions (especially those between the breaker panel) and inspect for more undone or loose connections.
normel
14 years ago
I would suspect a bootlegged ground on one of the receptacles, along with some phantom voltage readings to confuse things further.

A bootleg ground is one where a jumper is connected between the neutral screw and the ground screw on a receptacle. The receptacle will check as properly grounded when using a plug-in tester, but this is a dangerous and highly improper setup. Check each receptacle on that circuit.

Google "phantom voltage" to learn about this sometimes confusing phenomenon.
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Not necessarily. It may also mean that somewhere else on that same circuit there is a load which is drawing enough current to cause a 10v drop on the neutral conductor between the point where you're measuring and the neutral bar in the main service panel where your neutral and ground are bonded together. Turn off that breaker and see what loses power. Then switch those loads off, turn the breaker back on and remeasure the voltage. You should then get a 0v reading. If the circuit in question is being fed from a subpanel, then some of that 10v drop will be caused by current on the neutral feeder to the subpanel. Phantom voltages, as recorded by digital meters, are not normally found on wires connected to the service neutral bar. You will read a real voltage to ground on a neutral wire if your ground reference point is not solidly connected to the service ground bar or the service neutral is not solidly bonded to ground. If there is a neutral to ground voltage at the service, then you have a bonding problem that needs to be fixed.
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Ron Natalie
14 years ago
I don't think his ground is connected to any sort of ground bootlegged or otherwise (either neutral or the grounding conductor or some other ad hoc ground like the cold water pipe). Even with a high impedance meter, bootlegged-to-neutral (even from different circuits) would be close to zero rather than a phantom voltage and bootlegged-to-hot would be very close to the full 120.
dwichman
Original Author
14 years ago
Thanks for the feedback guys.

To clarify, I was doing both, replacing an existing receptacle with a GFI, and then adding a new one off the load terminals.

ronnatalie: You can NOT install countertop receptacles on a circuit that also feeds lighting.

Is this against code, dangerous, or otherwise? If so then I'd probably want to fix this as well.

I can tell you the 120V reading on the receptacle I added was not phantom, as I got a nasty shock when I was attaching the face plate screw and touched the range hood at the same time. This also tripped the upstream GFI, thankfully.
Ron Natalie
14 years ago
It's against code. There are to be at least two 20A circuits feeding the kitchen receptacle outlets and nothing else (with slight exception).

If it's really hot, you have both a disconnected ground and one touching hot somewhere. Someone has done a very sloppy job somewhere.
pharkus
14 years ago
Once upon a time, I lived in an apartment in Rumford, ME. One day, my microwave oven happened to come in contact with the side of my kitchen sink. There was a small light show, followed by my entire apartment losing power.

The whole building was knob & tube. Romex was attached to it in various spots, coming down to power the outlets. Factor #1.

Factor #2 was someone's decision to tie the ground wires to the neutral wires instead of finding real grounds.

Well, someone got hot and neutral backwards at one of the spots where it connected to the k&t.

So hot was neutral, neutral was hot, and ground was also hot.

Oops!

Hot ground wire and strange voltage readings on multiwire circuit

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Ron Natalie

normel

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Hot ground wire and strange voltage readings on multiwire circuit

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