Do you ever ground a gas pipe?

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mtnelectrical

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Essex, New Jersey
Today I got a call from a customer that has a small bakery shop. I wired all the fire suppresion system (exhaust range hood,make up fan, lights, etc) There is a cable that in case of a fire actuates the chemical, close the gas valve for range or oven and actuates the limit switches for the exhaust fan to work. The problem is that a steel cable that goes from the actuator box to the gas valve is broken (1/16" or so). Range hood installers went today to replace it but they found a sparkling situation. When they were about to replace the cable the saw a spark from the steel cable touching the raceway that contains this cable and they told the customer to call the electrician. When I got there start checking everything all my grounds are tight, cables looked good and found 7 volts from gas pipe to my grounded box. When I measured hot wire to ground 127volts and hot to gas pipe 123volts. I couldn't go to the basement (where the mains are)to check building ground. Tomorrow they will get the keys but how this pipe is getting this voltage to ground? Any ideas?
 
250.52(B)(1) ~ 2005/2002


It could be picking up a voltage from any of a hunded different sources (well, not really - we know the panel is the source.)

When was the last time ANY electrical work was done ~ including changing lamps?
 
Did they check/change any of the ballasts?

I'm recalling a job I did many years ago....I was still a helper and we were changing ballasts in a church kitchen. After handing a ballast up to the leadman, I leaning on the gas range...then put a hand over on the SS sink - I got hit with something.
After he replaced the ballast, I conducted an experiment ...leaning against stove and sink again. This time, I felt nothing.
We never really found what caused the difference in potential between the sink and stove - but, like I said, it seemed to have been cleared after replacing the ballast....maybe crumbling insulation and contact to the frame?
 
Someone(s) in the neighborhood probably has a loose neutral at their meter/disconnect and its sending some neutral current out their GES to the GES's of all the neighbors, and then back through their(your) neutrals to the xformer

If its possible to kill the main for a few seconds, you could clamp on probe the neutral and verify/disprove this possibility.

The gas line in this case is no better/worse than a rod/water bond for picking up other people's neutral leakage current.
 
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Around here the interpetation of 250.104(b) is that the gas is bonded to the electrode system. That way all water, gas, ground are the same potential. Former local code cycles allowed the bond to be at gas water heater, but now want service entrance of gas to main electric grounds and bonds.

Hows the voltage there? Could be anything, but check the obvious, all the gas appliances. Whats the voltage to neutral?
 
e57 said:
Around here the interpetation of 250.104(b) is that the gas is bonded to the electrode system. That way all water, gas, ground are the same potential. Former local code cycles allowed the bond to be at gas water heater, but now want service entrance of gas to main electric grounds and bonds.
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That is not an interpretation, that is a outright change from the NEC. :)

250.104(B) Other Metal Piping. Where installed in or attached to a building or structure, metal piping system(s), including gas piping, that may become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with 250.122 using the rating of the circuit that may energize the piping system(s). The equipment grounding conductor for the circuit that may energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.
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tonyi said:
Someone(s) in the neighborhood probably has a loose neutral at their meter/disconnect and its sending some neutral current out their GES to the GES's of all the neighbors, and then back through their(your) neutrals to the xformer

If its possible to kill the main for a few seconds, you could clamp on probe the neutral and verify/disprove this possibility.

The gas line in this case is no better/worse than a rod/water bond for picking up other people's neutral leakage current.
Click to expand...

I agree with Tonyi. I have seen this on 3 or 4 different occassions. It took us 3 days to find it the one time. We had to get local ahj involved to get access to HOs panel where the problem was located.
 
Tonyi,
The gas line in this case is no better/worse than a rod/water bond for picking up other people's neutral leakage current
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Not very likely....most gas utilities use an dielectric fitting at the meter to insultate the inside gas piping from the underground gas piping.
Don
 
don_resqcapt19 said:
Tonyi,

Not very likely....most gas utilities use an dielectric fitting at the meter to insultate the inside gas piping from the underground gas piping.
Don
Click to expand...
Not very likely....most gas utilities use an dielectric fitting at the meter to insultate the inside gas piping from the underground gas piping.
Click to expand...

How long have they been doing that? They do that here too, but on a lot of older places unless they have changed out the meter there isn't a dielectric fitting. In addition to that I have seen a number of Gas meters jumpered across with a bonding wire.
 
don_resqcapt19 said:
Tonyi,

Not very likely....most gas utilities use an dielectric fitting at the meter to insultate the inside gas piping from the underground gas piping.
Don
Click to expand...

I think most of the UG gas pipe around here is plastic.
 
Larry,
How long have they been doing that? They do that here too, but on a lot of older places unless they have changed out the meter there isn't a dielectric fitting.
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They were doing in the early 70s when I started in the trade.
Don
 
don_resqcapt19 said:
Larry,

They were doing in the early 70s when I started in the trade.
Don
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Don, with all your knowledge, I didn't thing you were such a youngster. They have been doing it here for at least that long, but some of the older places still have original meter without dielectric fitting.

What about the lightning protection that NFPA 780 or whichever one it is that says you have to bond to the grounding system? Are you familiar with that one?
 
Larry,
What about the lightning protection that NFPA 780 or whichever one it is that says you have to bond to the grounding system? Are you familiar with that one?
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The link that Bryan provided says that you can make the bond to the underground gas pipe via a spark gap. That would prevent any normal current flow on the gas piping. I think that the main reason that the gas utility used the dielectric fitting is because of the cathodic protection that they sometimes used on their piping. Now, as others have said, the pipe is all nonmetallic.
Don
 
Could the gas pipe that feeds the range be isolated ? Is there any electronic controls incorporated with the range? some leakage may be?
 
petersonra said:
I have to ask this. How is there any difference in using the UG gas pipe as a GE and just bonding it to the GE?
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Its not one of the (1)-(6) type electrodes. Gas is "other piping" so even though it may behave like an electrode as a leakage contributor, and needs a bond, its can't be considered an "electrode" per se.
 
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