All metallic electrical and mechanical systems, including all forms of gas piping, are vulnerable to lightning energy that enters a building during a nearby strike. Pipe dope used in black iron pipe joints deteriorates over time and leaks when exposed to lightning strikes.
When lightning strikes near a building, it may cause different electric potentials to form between the building’s pipes, wiring, and other metallic systems. If two metallic systems such as piping, wiring, coaxial cable, or metal ducts have greatly different electric potentials, an arc can form between them.
For this reason, metallic gas piping must be connected or “bonded” to an earth ground. NFPA 54: Section 7.13.2 code states: “CSST gas piping systems shall be bonded to the electrical service grounding electrode system at the point where the gas service enters the building. The bonding jumper shall not be smaller than 6 AWG copper wire or equivalent.”
Bonding enables the potential of all appliances connected to the electrical service to rise and fall equally. Where potential is equal, arcing is less likely to occur. When a CSST system is properly bonded to the electrical service, it helps reduce the difference in the electric potentials of two circuits, reducing the risk of arcing between them.
Currently, with regard to CSST, there is a conflict between the National Fuel Gas Code and the National Electrical Code.
National Fuel Gas Code (2009)
CSST gas piping systems shall be bonded to the electrical service grounding electrode system at the point where the gas service enters the building. The bonding jumper shall not be smaller than 6 AWG copper wire or equivalent. (7.13.2)
National Electrical Code (2011)
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. (250.104(B))
While the NFGC requires a minimum of a 6 AWG copper wire to bond CSST to the electrical ground, the NEC would allow a wire sized to handle the circuit that could energize the piping—that is the appliance rating. Furthermore, the NEC allows the use of the equipment grounding conductor (the bare copper grounding wire) to serve as the bond. In most cases, those wires will be smaller than 6 AWG—usually 14 AWG. While that size wire may be adequate for household current, it will not be sufficient to handle overvoltage situations such as transformer failures or lightning. That is why the CSST manufacturers lobbied for a change to the national codes to require bonding of all metal gas piping systems. This was partially successful at the NFGC, and work is continuing to bring the NEC toward that position. It is worth noting that a footnote to NEC 250.104(B) states, “Bonding of all piping and metal air ducts within the premises will provide additional safety.”
Another CSST technology that greatly reduces the risks of arcing is an energy-dissipating jacket that is applied over CSST piping to spread energy over a wide area. The energy dissipating properties improve the CSST’s ability to withstand damage due to arcing. The jacket also reduces the level of energy as it moves downstream, minimizing risks to regulators, appliance connectors, and other mechanical systems, all of which could contribute to the potential for fire.