The backstory:

My HVAC friend, my dad and myself installed new gas pipes in my house after the 40 y/o pipe started leaking. Suffice to say, the old pipe was beyond repair, every retightening of the pipe resulted in the next elbow becoming lose to the point, I would be tearing out drywall, air ducts and possibly beams to access it. So we ran new pipe.

We got the permit, had the county do the inspection. It passed, and we had Xcel (electric and gas utilities) come out and replaced the meter which was also old and leaking, and turn on the gas.

The setup passed inspection with a larger than needed ground wire going from the black pipe, near the meter, to a grounding pole going 5 feet underground. Xcel comes out today to replace the meter and hook up the gas and says my grounding wire cannot be there, that it will ruin the meter and rust the pipe where the wire clamps to the pipe and that a small current runs from my appliances to the meter. There is about 9 combined feet of pipe exposed outside, from the meter to where the pipe enters the house. I asked, what if lightning strikes the pipe and the Xcel guy says "Lightning will hit another part of the house first." So I call my HVAC, ask his opinion, I talk to a retired Master PLumber at Home Depot, and the county Fire Marshall and they all agree that it should be grounded. Oddly enough the Fire Marshall comments, "even if lightning hits the pipe, nothing will happen".

Remember, this is a black iron pipe installation, not CGGT. It is black iron pipe all the way from the meter to the room with the water heater and furnace. From the black pipe, a yellow flex pipe goes to the water heater, and a stainless steel flex pipe goes to the furnace.

So the plumbers and county is saying something different than Xcel. Should the pipe be grounded? Is bonding at the furnace enough?

Can I put a thin layer of something between the clamp and the black pipe? Foam, thin plastic, wax paper? The Fire Marshall suggested dirt ?!?

  • the national fuel gas code also requires the pipe to be bonded as well. – Arion Mitutoyo Dec 19 '15 at 2:09

According to National Electrical Code, the pipe has to be bonded. However, it can be bonded using the grounding conductor serving the equipment that uses the gas.

...The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means...

As for lightning strikes, the gas company is probably correct. It's not likely lightning will strike the pipe, especially since it's right next to a house.

National Electrical Code 2014

Chapter 2 Wiring and Protection

Article 250 Grounding and Bonding

250.104 Bonding of Piping Systems and Exposed Structural Steel.

(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 the service equipment enclosure; the grounded conductor at the service; the grounding electrode conductor, if of sufficient size; or to one or more grounding electrodes used. The bonding conductor(s) or jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.

  • 1
    As I understand physics, the real cause for grounding big metal objects in the house is not direct strike of lightning. It is that during storms people touching big ungrounded metal objects might get electrocuted because of electrostatic charge separation. – wigy Aug 19 '15 at 5:22
  • Storms have nothing to do with it. Imagine a gas stove that uses electricity for the timer, ignitor, etc. If an electric wire inside the stove breaks, it could touch the case of the stove. Now the stove is electrified. Touching it will result in a shock to the user. In addition, the gas pipe is electrified now, too, so any other gas appliances are potentially electrified. Think water heater or gas dryer. All of this danger is avoided by grounding the case of the stove and the gas pipe. – longneck Aug 20 '15 at 13:31
  • 2
    All grounded things in a building are REQUIRED to be connected together. The "earth" does not have a uniform voltage, so the area where your electric system is grounded may be a few volts different than the earth where your gas pipe goes. If they are not connected together, you could be shocked when touching the two grounded objects (since they are at different voltages). Connecting them together would force them to have the same voltage, removing the risk of shock. – Pigrew Dec 19 '15 at 5:05
  • @longneck Grounding the equipment like a stove is designed to trip the breaker, since the grounding conductor is connected back to the neutral, and if the hot wire is connected to the grounding conductor, the breaker will trip. Grounding an appliance doesn't just make it safe through being connected to the ground, what makes it safe is turning off the power. – Steve Sether Oct 18 '20 at 15:53

The issue of accelerated corrosion is true. Current can flow from the electrical system through the gas pipe, through the meter and outside. This can cause corrosion due to any different metals used between the two systems, and due to current flow.

It's also true that you have to ground your gas pipe according to the NEC. Even if you did what the gas company employee said and disconnect the ground wire, any stove or gas dryer is going to connect the metal parts of the appliance to both the electrical ground wire, and the metal gas pipe.

So how do you solve these two problem? Generally this is solved through the gas piping in your house being connected to the meter via a dielectric union. The dielectric union connects two sets of pipes together, but electrically isolates one from another by an insulator. It protects against both "stray current", and any corrosion due to a galvanic reaction between dis-similar metals.

I'm not sure why the XCEL employee didn't know about this.


Always bond everything metalic to the common ground

  • 3
    Hello, and welcome to Stack Exchange. We're looking for more than just one-line answers, e.g. what does "everything metallic" mean? Gutters? – Daniel Griscom Jun 9 '18 at 16:42

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