The gas company technician has turned gas off to the gas meter because he detected .4 volts coming off the gas pipe leading to our furnace. The meter was disconnected when he tested the pipe. He stuck a screw driver in the soil to use as a ground and then put the multi meters red lead on the pipe to show .4 volts. However, when tested at the furnace using its ground there is no voltage at all on his multimeter. Any ideas on what the discrepancy is caused by? I have done my own tests at multiple different properties and consistently get .3-.6 volts on gas meters using a Fluke 117. So, is this normal?
I agree with Ed Beal. The technician had no idea what they were doing.
The gas pipe is required to be bonded yes, but the equipment ground that serves the electrical circuit for the furnace is allowed to be the sole means of that bonding.
From the 2017 National Electrical Code (also in earlier versions)
(B) Other Metal Piping. If installed in or attached to a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to any of the following:
(1) Equipment grounding conductor for the circuit that is likely to energize the piping system. ...
You said --
However, when tested at the furnace using its ground there is no voltage at all on his multimeter.
This tells me your equipment grounding conductor for the gas furnace circuit is in good condition.
A millivolt signal to a screwdriver stuck in the ground is not a reliable way to do earth ground testing.
The Utility should immediately restore your service and that technician needs to be properly trained.
This is completely wrong! The screw driver is not a proper ground rod.
I think the proper grounding is at least 8 feet for a ground rod. It is possible also that some ground rods are no longer at 'ground' potential which is why they can get replaced every now and again - so people can get a bad reading. Typically this is checked with a megger. I said that to say this - did he check his screwdriver with a megger to make sure it was correctly at ground?
NEC 250.52(A)(5) states: “Rods and pipe electrodes shall not be less than 2.44 m (8 ft.) in length.” ... With regard to diameter requirements, NEC 250.52(A) (5)(b) states, “Grounding electrodes of stainless steel and copper or zinc coated steel shall be at least 15.87 mm (5/8 in.)
So considering that - does the Gas Technicians Screw Driver match those requirements ?
If he had a 5/8 inch diameter screw driver eight feet long plus handle that he drove into the ground then he is right; otherwise, as others have said call the gas company back out and have them send someone else.
Yes, I think the gas company tech is completely out of his league. Additionally, he is trying to enforce a testing program designed by someone just as far out of his element. 4/10 of a volt wouldn't even qualify as phantom voltage much less intrinsically safe voltage. You can walk across dry carpet and produce more than that. I hate to say it but you need a lawyer. The utility company is required by law to supply you with gas as long as you pay your bill and your system does not present a hazard to yourself, your neighbors or the utility itself. Good Luck. P.