Objectionable current on gas main

P

pipe_bender

Member
Location
Boston
Occupation
Electrician
Hello all, dealing with a 'objectionable' current issue a pipe fitter noticed a spark when taking apart some gas pipes, he said he took a jumper cable from his truck to reconnect the pipes while he worked on them and the cable also sparked.
There are 6 units so 6 gas maters, the pipe in question goes to an apartment, and after getting a clamp meter that fit over the pipe I measure about 1-2 amps on the pipe. I don't see any wires touching gas pipes its a older building.
Any ideas on where to start looking, or dare I ask is this a possibly a non-issue?
They were going to relocate some other old gas lines using the newer flex stuff but the pipe fitter wants the current off the gas pipe.
 
There will always be EGC connections to the interior gas piping, and if there are parallel paths to other electrical systems in the area, via the gas piping there will be current flow.
With all of the piping being metallic, it will be a parallel path for neutral current between all of the services in the building.
 
Is does each unit have its own service or set of service entrance conductors or is each one fed by a feeder? If the former, I agree with Don there will be current flowing on it, nothing you can do except throw in a dielectric union. If it's the latter, you might want to investigate further could be a neutral ground Bond somewhere there's not supposed to be.
 
electrofelon said:
Is does each unit have its own service or set of service entrance conductors or is each one fed by a feeder? If the former, I agree with Don there will be current flowing on it, nothing you can do except throw in a dielectric union. If it's the latter, you might want to investigate further could be a neutral ground Bond somewhere there's not supposed to be.
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OK thanks, hmmmmm if I remember right the service is a all in one meterpack with meters and main breakers for all the units, looked newer than the panels in the units. When I go back I'll shut off the main for that unit and see if the current goes away.
 
Checked it out again and this time there was 6 amps on the gas pipe, turning off the main breaker to the unit made it drop but not to zero, the only gas appliance in the apartment is a extremely heavy gas range / convection oven. Turning off the breaker to the range did not change much.
 
An old range with frame bonded to neutral, especially if fed from a subpanel, could easily cause this if gas is bonded to ground elsewhere. It would not necessarily matter when the range breaker is turned off because all neutral current from the subpanel could potentially take the gas as a parallel path. For example subpanel neutral bar > range frame > gas pipe to water heater > hot-cold-gas bonding at water heater > cold water pipe to water service entrance from ground > grounding electrode conductor to meter pack. This is just one possible example I could think of, there could be many possible such configurations in a multi-unit building like this. I mention the hot-cold-water bonding because this is something many AHJs around here require. But as folks on this forum have mentioned, it should not be necessary if gas appliances bond the gas pipe to the EGC for the appliance, and it can create parallel paths like you're apparently discovering.

Old appliances with bare neutral conductors that bond frames are only allowed to be connected to service panels, i.e. the meter pack in this case, not subpanels in the units. Basically for this kind of reason. Providing a separate EGC to the range or removing the additional gas bond could be solutions.

It could of course also be something else.
 
Is there any current on the feeder EGC as well?

From the service to the apt sub panel?

Or on the range egc to the subpanel?

Can you also verify that the subpanel doesn't have a neutral to EGC bond in the unit?
 
We know that current is a result of voltage between points, but it doesn't tell us which point (if either) is genuinely at zero volts (and to what reference?) and which has become energized.

It's possible that the appliance is at zero volts and it's the incoming gas line that is being externally energized somehow. Earth-bound gradients, a neighbor with service neutral issues, etc.
 
LarryFine said:
We know that current is a result of voltage between points, but it doesn't tell us which point (if either) is genuinely at zero volts (and to what reference?) and which has become energized.

It's possible that the appliance is at zero volts and it's the incoming gas line that is being externally energized somehow. Earth-bound gradients, a neighbor with service neutral issues, etc.
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Gas services have dialectic unions at the gas meter. Gas company wants its piping electrically isolated to prevent issues with cathodic protection. Issue reported is on customer side of gas meter
 
jaggedben said:
Old appliances with bare neutral conductors that bond frames are only allowed to be connected to service panels, i.e. the meter pack in this case, not subpanels in the units.
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I don't think that's how 250.140 reads in the 2023, I'll have to take a closer look at my 2023 code book later.
 
jaggedben said:
An old range with frame bonded to neutral, especially if fed from a subpanel, could easily cause this if gas is bonded to ground elsewhere. It would not necessarily matter when the range breaker is turned off because all neutral current from the subpanel could potentially take the gas as a parallel path.
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If the neutral is working correctly why would there be current on the gas pipe though?
 
ramsy said:
Switch each branch breaker on & off to find the culprit(s)
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Might not be isolated to a single unit but an issue that is being combined by every unit. If every unit was wired the same, then that could also be why turning the main breaker to the unit off only dropped it by a little. (Post #5)
 
As long as Ultility companies only supply one high voltage lead to thier thousands of distribution transformers this will be a potential problem. I have measured current flow on several houses copper water & steel gas supplies. Even with the meter removed and no power have measured 0.25 amps on copper water piping and less in steel gas pipe. Appears they are using the neutral to back feed the auto transformer where one side of primary winding is connected to 120/240 volt center tap. Before my block was ten years old underground steel gas lines started to leak. Several times when we went away for a weeks vacation came home to gas odor and called the gas company. They never found anything. Ended up buying a couple of screened things with vents to install in two separate bedroom windows to get some air flow. Twenty or so years later while the gas company was repairing neighbours gas line they found
my steel gas pipe was leaking. They pull a plastic liner thru old steel pipe and glue it at both ends. When I questioned one of the utility linesman he tried to tell me that the #4 aluminum ground wire going to a 8' ground rod at bottom of pole takes the place of a second high voltage lead. Told him here in the big city my pole does not have a inch of surface dirt within 25' of ground rod and good luck with even getting 100 ohms measurement especially in winter time. Sad part the pole that feeds my distribution has three phase ( 3 wires ) 13,200 at top of pole. Same cost cutting up itself company does not install the first ten feet of aluminum ground wire in PVC conduit or outer guard and when druggies steal bottom section of ground rod conductor can take them months to repair. Just wondering if lightning was to hit a pole transformer with only one primary wire feed and open ground rod how much current could possibly flow thru my copper water service & steel gas pipe.
 
electrofelon said:
moving to two bushing transformers fed line to line would not fix the problem.
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Would it not eliminate the possibility of stray utility primary neutral current (during a fault or open) at 7200V crossing the customers property such as a pool?
But yeah secondary no way to eliminate that, secondary is 120V to ground so not going far thru dirt.
 
tortuga said:
Would it not eliminate the possibility of stray utility primary neutral current (during a fault or open) at 7200V crossing the customers property such as a pool?
But yeah secondary no way to eliminate that, secondary is 120V to ground so not going far thru dirt.
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Yes getting rid of the MGN system would of course eliminate some utility stray current issues. But I claim that the vast majority of stray current issues us electricians deal with would remain,
 
garbo said:
As long as Ultility companies only supply one high voltage lead to thier thousands of distribution transformers this will be a potential problem. I have measured current flow on several houses copper water & steel gas supplies. Even with the meter removed and no power have measured 0.25 amps on copper water piping and less in steel gas pipe. Appears they are using the neutral to back feed the auto transformer where one side of primary winding is connected to 120/240 volt center tap. Before my block was ten years old underground steel gas lines started to leak. Several times when we went away for a weeks vacation came home to gas odor and called the gas company. They never found anything. Ended up buying a couple of screened things with vents to install in two separate bedroom windows to get some air flow. Twenty or so years later while the gas company was repairing neighbours gas line they found
my steel gas pipe was leaking. They pull a plastic liner thru old steel pipe and glue it at both ends. When I questioned one of the utility linesman he tried to tell me that the #4 aluminum ground wire going to a 8' ground rod at bottom of pole takes the place of a second high voltage lead. Told him here in the big city my pole does not have a inch of surface dirt within 25' of ground rod and good luck with even getting 100 ohms measurement especially in winter time. Sad part the pole that feeds my distribution has three phase ( 3 wires ) 13,200 at top of pole. Same cost cutting up itself company does not install the first ten feet of aluminum ground wire in PVC conduit or outer guard and when druggies steal bottom section of ground rod conductor can take them months to repair. Just wondering if lightning was to hit a pole transformer with only one primary wire feed and open ground rod how much current could possibly flow thru my copper water service & steel gas pipe.
Click to expand...
That would be a singe wire earth return and is never used in populated areas. The utility uses a common conductor as the neutral for both their high voltage distribution and the secondary of the transformers that supply power to their customers.
 
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