Does the NEC require a separate ground wire to the gas line?

Usually no. NEC 250.104(B) permits the equipment grounding conductor of the circuit serving the gas appliance to serve as the bonding means for the metal gas piping.

Does CSST need a bonding conductor?

Most uncoated CSST products require a direct bond, commonly 6 AWG copper to the grounding electrode system. NEC 110.3(B) makes the manufacturer instructions enforceable, so follow the listing for the specific product.

Do I have to bond the gas line to the electrical panel?

Q: Can gas pipe be used as a grounding electrode?

No. NEC 250.52(B)(1) prohibits metal underground gas piping systems from being used as a grounding electrode.

The gas line has to be bonded, but usually not with a separate wire run back to the panel. Section 250.104(B) is more forgiving than most people expect, and the real driver on modern jobs is the CSST manufacturer instructions.

What 250.104(B) requires

Section 250.104(B) states that metal piping systems, including gas piping, that are installed in or attached to a building or structure and are likely to become energized shall be bonded to any of the following: the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or one or more grounding electrodes used. The bonding conductor is sized in accordance with Table 250.122 using the rating of the circuit that is likely to energize the piping.

Then comes the sentence that resolves most gas line questions. The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. A gas furnace or gas water heater with an electric ignition already has a 15 or 20 ampere circuit landed on it with a 14 or 12 AWG equipment grounding conductor. That equipment grounding conductor bonds the gas piping through the appliance. No additional wire is required by the NEC.

Gas pipe is not an electrode

Section 250.52(B)(1) explicitly prohibits metal underground gas piping systems from being used as a grounding electrode. Bonding and grounding are not the same thing here. You bond the gas system so that a fault cannot leave it energized. You never use it as an electrode.

Where CSST changes the answer

Corrugated stainless steel tubing has a thin wall and is vulnerable to arc puncture from a nearby lightning event. Manufacturers of uncoated CSST typically require a direct bond, commonly a 6 AWG copper conductor from the rigid pipe at the point the CSST leaves the meter or manifold, run to the electrical service grounding electrode system, with a specific clamp. Section 110.3(B) requires listed equipment to be installed per its instructions, so that manufacturer requirement is enforceable as code. Some black jacketed arc resistant CSST products are listed without the additional bond, and the instructions will say so. Read the instructions for the specific product on the job.

Other piping and structural steel

Section 250.104(A)(1) is a separate and stricter rule for metal water piping, which requires a bonding jumper sized per Table 250.102(C)(1) run to the service equipment or grounding electrode conductor. Section 250.104(C) covers structural metal that is interconnected to form a building frame. Do not apply the water pipe sizing table to gas piping. Gas piping falls under 250.104(B) and Table 250.122.

Field takeaway

For traditional black iron gas pipe feeding an electrically supplied appliance, the appliance circuit equipment grounding conductor is the bond and nothing extra is required. For CSST, read the manufacturer instructions and expect a 6 AWG direct bond back to the grounding electrode system.