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.
Click to expand...
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.
 
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