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Discussion Starter · #1 ·
Got a call that the plumber was getting shocked, and seeing sparks when replacing a gas line.

He was replacing the main gas line from the meter into a house. I could see black marks where he was trying to couple a gas flex line to the rigid. It melted some of the rubber coating on his metal flex line.


Thought for sure the house or someone else's lost a neutral. Called the Utility Co. and he load tested the service looking for open neutral, everything looked good.

Measured about 2 volts between the gas line pipes. Turned off the main and it disappeared. I bonded the gas pipe to the cold water ground and verified the service bonding and rod connections.

Any ideas ?
 

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Discussion Starter · #6 ·
Underground power lines for
Air Conditioner,
garage,
landscape lighting ,
Exterior Lighting attached to metal siding,
Shorted gas appliance,
Bad grounding for the house.

Did you try shutting of one breaker at a time and see if it was a particular circuit?
Yes we shut of one breaker at a time, and multiple breakers stopped the 2 Volts

unplug all gas appliances and check again
Didn't try that

I know of a plumber who was getting shocked connecting a copper water main to a house. Same deal, utility came out and checked everything in the house and it was OK. It turned out to be hot wire buried in the ground for a neighborhood street light that was never installed.
Could be a neighbor or something outside using the neutral from this house, but I did get the 2 volts to stop when I turned off the main. When the plumber was working last night, he said it really started when the tenant came home. Had to be 120V or up there. He said he was getting bite pretty good.
 

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Discussion Starter · #7 ·
Underground power lines for
Air Conditioner,
garage,
landscape lighting ,
Exterior Lighting attached to metal siding,
Shorted gas appliance,
Bad grounding for the house.

Did you try shutting of one breaker at a time and see if it was a particular circuit?
Even if the ground was weak to the house, why is there voltage on there ? Enough to do what it did.
 

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Even if the ground was weak to the house, why is there voltage on there ? Enough to do what it did.
High impedance to the grounding system can cause current to flow through all the bonded stuff in the house, and bonded to the gas line had to lowest impedance to ground, may still be high enough to not let enough current to flow to trip a breaker.
 

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Bilge Rat
motors and controls.........
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9,515 Posts
Turning off circuits in the house and having the voltage disappear points strongly to an issue within the house.

Try measuring voltage across the gas pipes while turning on circuits on one leg only. Load these circuits.

Then turn everything off and do the same with the other leg.

If voltage increases with load on one leg only (either one, not both), the problem is almost certainly a bad neutral in the house you're working on.
 

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was one of the breakers that stopped it to a gas fired appliance ? boiler, furnace transformer ? water heater ? you know the drill.
 

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Discussion Starter · #15 ·
Turning off circuits in the house and having the voltage disappear points strongly to an issue within the house.

Try measuring voltage across the gas pipes while turning on circuits on one leg only. Load these circuits.

Then turn everything off and do the same with the other leg.

If voltage increases with load on one leg only (either one, not both), the problem is almost certainly a bad neutral in the house you're working on.
Yes a difference in potential but not enough to register on a couple meters. Poco load tested neutral at this house. All is good on their side. Could be a neighbors house using this houses neutral.

was one of the breakers that stopped it to a gas fired appliance ? boiler, furnace transformer ? water heater ? you know the drill.
Didn't get into that. My Fluke nor the Pocos registered voltage, only my Klein which I don't trust that much. Was a small amount.
 

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I had this happen, a friend called and said the gas line in her guest house was smoking where it passed thru a plaster ceiling with metal lath. She also said she had been getting shocked in the shower prior to this. I raced over there (to check out the gas line, not her in the shower you filthy pigs) and sure enough, the ceiling around the gas pipe was all black and burned.

Turned out to be a couple of things that had gone wrong.
1. Guest house sub panel was wired with 2 hots and a neutral, emt for grounding.

2. The emt came apart on the rooftop

3. Someone was "handy" and had added two circuits, landing the neutrals on the grounding bus in the sub panel.

The neutral current for the two added circuits could no longer use the emt to return so it travelled down the grounding conductor to the furnace, which was plug and cord, and from there went to the gas line, over to the gas water heater, and finally onto the water pipes then home. Unplugging the gas furnace would stop it, but it would also cause the grounding system in the house rise to 120 volts, and of course stop the two added circuits from working. The metal lath in the plaster was in loose contact with the gas and water pipes, which accounted for the heat at that spot.

So you could have an open neutral, but you won't see much voltage once the piping is put together. Once the piping is opened, watch out!

Upon examination of the main panel there were scorch marks at the locknut where the emt emerged from the neutral current using that path before the emt completely separated on the roof top.
 

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Discussion Starter · #18 ·
I had this happen, a friend called and said the gas line in her guest house was smoking where it passed thru a plaster ceiling with metal lath. She also said she had been getting shocked in the shower prior to this. I raced over there (to check out the gas line, not her in the shower you filthy pigs) and sure enough, the ceiling around the gas pipe was all black and burned.

Turned out to be a couple of things that had gone wrong.
1. Guest house sub panel was wired with 2 hots and a neutral, emt for grounding.

2. The emt came apart on the rooftop

3. Someone was "handy" and had added two circuits, landing the neutrals on the grounding bus in the sub panel.

The neutral current for the two added circuits could no longer use the emt to return so it travelled down the grounding conductor to the furnace, which was plug and cord, and from there went to the gas line, over to the gas water heater, and finally onto the water pipes then home. Unplugging the gas furnace would stop it, but it would also cause the grounding system in the house rise to 120 volts, and of course stop the two added circuits from working. The metal lath in the plaster was in loose contact with the gas and water pipes, which accounted for the heat at that spot.

So you could have an open neutral, but you won't see much voltage once the piping is put together. Once the piping is opened, watch out!

Upon examination of the main panel there were scorch marks at the locknut where the emt emerged from the neutral current using that path before the emt completely separated on the roof top.
I've seen something like what your describing before where the bootlegged neutral caught a wood floor on fire when the Plumber cut the galvanized water pipes.
 

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Discussion Starter · #19 ·
"and multiple breakers stopped the 2 Volts"


Trace and megger those circuits, something is shorting to ground/duct work/piping.


Any large appliances on them?
One circuit I could see, but multiple eliminates a short in my mind. The voltage was so small, it only registered on one meter out of 3. Maybe at dusk when people come home either there, or at the neighbors is when to test.
 
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