Help me troubleshoot a 20v ground leak in my house :(

[jonny290]

Here's the situation. earlier this week I went outside to put up a couple of antennas. This required of course that I ground the mast and coax shield to earth outside.

Well, once I grounded the antennas, I was getting sparks when I connected the radio ground (at internal, 'house ground' potential) to the antenna ground (outside, true earth potential).

I rent this house with my friend, from his mom and stepdad. His stepdad (an electrician, though it's been a few years since he did any real work)came over today and we spent about four hours troubleshooting.

Here's the lowdown.

We're measuring about 20 V AC from hot to ground and 14-15 V AC from neutral to ground on this circuit. All other circuits have 0 (or less than 0.1) V AC from hot-ground and neutral-ground.

The only things on this circuit that we can identify:

Three outlets in my room
a fishtank in the kitchen
a small attic vent fan

The problem exists even after disconnecting everything in my room, the fishtank pump *and* the attic fan.

We've redone the breaker box grounds and double-checked all accessible junction boxes and lines for any weird stuff hanging off it, or wiring flaws - have found none.

Our next step is just to put in a virgin run of 12/3 (or whatever the hell is most appropriate) from the junction box to my room. This will be a six-hour PITA job, because the breaker box is on an outside wall, and the roof has a very low pitch (read: we can't get to the last few feet of in-attic horizontal run before it turns down for the JB).

House is approx. 30 years old, your typical ranch home of the 70's.

Any thoughts on other stuff we can check before we run a new circuit?

 

[crayon]

Since you have isolated the problem to this circuit, disconnect the outlets and *anything* from the circuit. This will isolate the problem down to either recep's or wireing.

Remeasure. If you get something, then it has to be wiring. If not, rehook up the recep's one at a time and remeasure.

 

[benjaminarthurt]

Just a guess but maybe a loose neutral line...

 

[N_Jay]

Have you told the house owner?

He should be fixing it, not you.

If he asks you to fix it, then you should hire a licensed electrician and have him pay.

It is not an issue that I think it is that difficult or that you can't do it. It is the fact that it is RENTAL property, and if there was problem later you could be help responsible.

You are allowed to do wiring in YOUR OWN HOME, but this is NOT your home!

 

[jonny290]

Allow me to clarify - House Owner is Roommates Stepdad. He's doing all the work (read: anything that's got to be to code) and I'm just brainstorming and helping him isolate circuits. We're being safe, buddy system, breaker double-checks, etc.

We talked, and he agreed that if this becomes too big a bite for him to chew, that we'll call in a professional electrician. We believe, however, that we can nail this down in an afternoon or two more of work.

Said that he's never seen a wiring fault at this consistently low voltage in 35 years of repair work. Either it's the full 110 and burns a circuit out, or it dissipates.

 

[crayon]

For my nearsighted friend N_Jay :

I rent this house with my friend, from his mom and stepdad. His stepdad (an electrician, though it's been a few years since he did any real work)came over today and we spent about four hours troubleshooting

 

[N_Jay]

Allow me to clarify - House Owner is Roommates Stepdad. He's doing all the work (read: anything that's got to be to code) and I'm just brainstorming and helping him isolate circuits. We're being safe, buddy system, breaker double-checks, etc.

We talked, and he agreed that if this becomes too big a bite for him to chew, that we'll call in a professional electrician. We believe, however, that we can nail this down in an afternoon or two more of work.

Said that he's never seen a wiring fault at this consistently low voltage in 35 years of repair work. Either it's the full 110 and burns a circuit out, or it dissipates.

Look for a bad lighted switch, or an appliance with bad insulation (common on old refrigerators)

Don't assume it is s constant voltage, try drawing some current, it will probably go down.

It could even be wet wire and cracked insulation.

If his license is not current he may not be allowed to do electrical work on a house he owns if he rents.

 

[KD8CES]

Have you penetrated a direct burial cable in the yard leading to a shed, or low voltage lighting when installing the ground rod or anything, or perhaps an underground dog fence that is backfeeding your circuit somewhere? How about a water pipe ground wire that may have a hot source touching the water pipe somewhere? Bad heat tape wrap on the pipe? or an extension cord laying in water or damp in the socket? hope these help nail it down. Scannerdweeb.

 

[Dubbin]

Did you unplug the heater thats in the fish tank?

 

[James]

We're measuring about 20 V AC from hot to ground and 14-15 V AC from neutral to ground on this circuit. All other circuits have 0 (or less than 0.1) V AC from hot-ground and neutral-ground.

Measuring 20 V (to ground) with cicuit breaker off ?

Is this a 3 wire circuit, ie 2 "hots" sharing a neutral ?

What type of grounding do you have at the electric service, ie meter box, service panel ?
Single ground rod ? ( Sounds like you have inadequate earth ground at service equipment)

Is the plumbing metallic, ie copper, galvanized ? If so is it bonded to the service ground ?

 

[jonny290]

Measuring 20 V (to ground) with cicuit breaker off ?

Is this a 3 wire circuit, ie 2 "hots" sharing a neutral ?

What type of grounding do you have at the electric service, ie meter box, service panel ?
Single ground rod ?

Is the cold water piping metallic, if so is it bonded to the service ground ?

20v with breaker on. 0 volts between all pins when breaker is off.

it's a conventional hot/neut/ground circuit. Wiring is white/black/copper.

We have two rods outside - one is unconnected and the other has a solid 6 gauge ground wire to breaker box. Confirmed ground rod -> breaker box resistance at 0.0 ohms.

Cold water piping is metallic and is bonded, we checked. 0.1 ohms resistance between breaker box and a 'dry all day' kitchen sink(so I'm confident that was metal conducting, not water).

 

[N_Jay]

Where is the 20V again?

Neutral to Box G?
Neutral to "other G"?

 

[James]

20v with breaker on. 0 volts between all pins when breaker is off.

I'm sorry, I'm still missing something, with CB on, you should be getting 110-125 V.
You say with CB on you ONLY get 20 V ?

 

[Thayne]

I would have the Electric utility that serves the house check their neutral connections at both the transformer Center tap and also where the service drop or lateral connects to the house; and also the connections inside the meter housing. If any of these is a poor connection, the only way the neutral current can flow back to the source is thru the grounding system for the house. A lot of times the crimp connetors they use on the aluminum wire get loose & corroded. I have seen it cause lots of weird voltage readings

 

[James]

I would have the Electric utility that serves the house check their neutral connections at both the transformer Center tap and also where the service drop or lateral connects to the house; and also the connections inside the meter housing. If any of these is a poor connection, the only way the neutral current can flow back to the source is thru the grounding system for the house. A lot of times the crimp connetors they use on the aluminum wire get loose & corroded. I have seen it cause lots of weird voltage readings

Agreed. Where I live squirrels are a MAJOR problem on overhead service drops. They love to gnaw on power lines.
Underground poses alot of other problems, esp. aluminum conductors.
Have you noticed lights dimming, or getting brighter with varying household load ?

Also, even if you have verified it is not a 3 wire circuit, at some time someone may have "picked up" a neutral off this circuit. In other words another circuit (possibly same phase) may be sharing the neutral path (conductor).
If you can identify the neutral at the panel, disconnect it and see if any other circuits are affected (stop working). Shut off the main before doing so. You may get an arc. depending on load.

 

[jonny290]

I'm sorry, I'm still missing something, with CB on, you should be getting 110-125 V.
You say with CB on you ONLY get 20 V

This is correct.

Breaker on:

Hot-neut - 115-118v
Hot-ground - 20v or so
Neut-ground - 14v or so

this is all AC

breaker off:

hot-neut: 0v
hot-ground - 0v
neut-ground - 0v

It's the weirdest thing.

And yeah, we were using a known good digital VOM and did well over two dozen tests this morning - those numbers are accurate.

The power 'feels' consistent. We never get brown/blackouts. I have approximately 600 watts of gear on this circuit including a computer with two monitors, a 14 space rack full of digital audio gear and two 25 watt lamps. Hasn't ever blown a breaker, and my gear consistently works fine with no problems.

 

[James]

This is correct.

Breaker on:

Hot-neut - 115-118v
Hot-ground - 20v or so
Neut-ground - 14v or so

Ok, so we know (can assume) you have an open ground. Thats a good place to start looking.
Man! Troubleshooting thru a forum is gonna be tough
If you have an open (broken) earth (equipment) ground, any voltage; say off the chasis of a piece of equipment is gonna find the "path of least resistance" to ground. In this case your antenna.

 

[jonny290]

That's our current theory, that this circuit just does *not* have a ground.

The more that we hash it out here, the more I'm thinking that just running new romex or whatever is going to be the simplest and safest solution to this one.

 

[N_Jay]

This is correct.

Breaker on:

Hot-neut - 115-118v
Hot-ground - 20v or so
Neut-ground - 14v or so

this is all AC

breaker off:

hot-neut: 0v
hot-ground - 0v
neut-ground - 0v

It's the weirdest thing.

And yeah, we were using a known good digital VOM and did well over two dozen tests this morning - those numbers are accurate.

The power 'feels' consistent. We never get brown/blackouts. I have approximately 600 watts of gear on this circuit including a computer with two monitors, a 14 space rack full of digital audio gear and two 25 watt lamps. Hasn't ever blown a breaker, and my gear consistently works fine with no problems.

The ground is not connected and is floating.

If the ground was tied to anything, then the hot to gnd and neutral to gnd would add up to the 115-118.

There is a chance that the ground of the house is not tied to the neutral in the BCB box (the ONLY place that neutral and GND should ever touch.)


You scanner power supply is probably leaking some so its chassis GND (and the antenna shield) floated up to 55V or so, and that is where the sparks came from.

I will bet you

 

[James]

That's our current theory, that this circuit just does *not* have a ground.

The more that we hash it out here, the more I'm thinking that just running new romex or whatever is going to be the simplest and safest solution to this one.

With only 20V to ground, your "theory" is correct you should have the same reading from hot/neutral as hot/grnd.
Identify all outlets (plugs *and* switches) on the circuit. See if any have a grnd.
If you find one that is grounded, you should be able to isolate the break.
Someone may have not twisted the conductors together in a j box. Also some electricians solder their twists, if thats the case, the copper can become brittle, (too much heat) and break.