Bonding is provided primarily to prevent a possible electric shock hazard for persons coming into contact with the gas piping and other metal objects that are connected to the grounding system, but which may be energized at a different level of electrical potential. Gas piping can become energized by an electrical fault in the branch circuit of a gas appliance connected to the piping system. Nearby lightning strikes can also result in an unbalanced voltage build-up and a resulting high electrical potential difference. That potential can cause an electrical arc between the gas piping and another nearby metallic system such as the copper water piping or electric wiring or structural steel. The arc may cause damage to certain gas tubing systems.
NEC® REQUIREMENTS The NFPA 70, National Electrical Code requires all above ground metallic piping (water, gas, electrical conduits, etc.) be bonded. Article 250 in the NEC® contains extensive coverage for the grounding and bonding of electrical and other metallic systems. The specific types of grounding electrodes and acceptable methods of bonding gas piping systems to them are found in Sections 250.52, 250.70 and 250.104(B).
The NEC® requires that all separate grounding electrode systems (including lightning protection systems) be bonded together to establish an equal potential state between these systems. NEC® Section 250.104 (B) requires that any metal piping including gas piping that is likely to become energized be bonded to the grounding electrode system. The NEC® also states that bonding of metallic systems, as a general practice, will provide additional safety.
DEFINITIONS The following terms and definitions are commonly used to describe technical requirements: Bonded (Bonding): Connected to establish electrical continuity and conductivity. Bonding Jumper: A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected. Grounded (Grounding): Connected (connecting) to ground or to a conductive body that extends the ground connection. Grounding Electrode Conductor: A conductor used to connect the system grounded conductor or the appliance to a grounding electrode or to a point on the grounding electrode system.
Grounding Electrode System: The NEC® describes the grounding electrode system and its installation in Sections 250.50 to 250.53. Electrodes can be a metal rod/pipe/plate driven into the ground; the metal frame of a building; buried metal water piping; a ground ring of copper wire; or a concrete encased foundation electrode. Buried metal water piping can not be used as the sole grounding electrode, but must be bonded to a second grounding electrode such as a driven rod (250.53).