Judging by the responses to NECA’s online “Code Question of the Day (CQD),” gas piping and its use in bonding and grounding sure generated controversy and explosive comentary. The following questions and answers should clarify what many readers are asking.
QUESTION: How do I size the bonding jumper used to bond metal gas piping?
ANSWER: Section 250-2(c) requires the bonding to be to the supply system grounded conductor. I understand that as meaning that the sizing should be done according to Section 250-66. Section 250-104(b) requires that the bonding be to the grounding electrode system, which I consider also to mean in accordance with Section 250-66.
There is some argument regarding the use of Section 250-104(c), which requires other interior metal piping to be bonded in accordance with Table 250-122, based on the rating of the circuit that may accidentally energize the piping. My opinion is that metal gas piping is not included in Section 250-104(c) for other reasons. It may be run on the outside as well as the inside of the building, and its exposure to lightning would require it to be sized according to Section 250-66. It may be difficult to pinpoint which circuit(s) have the potential to energize a metal gas pipe run through a building.
QUESTION: When I connect the gas piping to my clothes dryer or to any other grounded gas-fired appliance with electrical components, isn’t the metal gas piping system in the building automatically grounded and the requirements of Section 250-104(b) satisfied?
ANSWER: Many people believe that, but I am not one of them. The gas piping system is undoubtedly grounded by means of the equipment grounding conductor connected to the gas appliance, but how can we say the requirements of Section 250-104(b) are satisfied? This section clearly requires that the metal gas piping be “electrically continuous and bonded to the grounding electrode system.”
Relying on an appliance to ensure electrical continuity is incorrect. Removal of the appliance would eliminate the bonding of the entire gas piping system. For this reason bonding by means of the equipment grounding conductor run to the appliance does not meet the requirement of bonding metal gas piping “to the grounding electrode system.”
QUESTION: Does the National Electrical Code require interior metal gas piping to be grounded?
ANSWER: Section 250-2(c) reads as follows: “Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials, such as metal water piping, metal gas piping, and structural steel members, that are likely to become energized shall be bonded as specified in this article to the supply system grounded conductor or, in the case of an ungrounded electrical system, to the electrical system grounded equipment, in a manner that establishes an effective path for fault current (italics added for emphasis).”
Based on that wording, the answer is either “yes” or “maybe.” The difficulty is in the wording “that are likely to become energized.” At this point, it appears to be a judgment call for the “Authority Having Jurisdiction.”
Section 250-104(b) reads as follows: “Metal Gas Piping. Each aboveground portion of a gas piping system upstream from the equipment shutoff valve shall be electrically continuous and bonded to the grounding electrode system.”
This appears to take the “maybe” out of the answer. This section’s requirements are explicit in that not only interior gas piping, but also that each portion of an aboveground gas piping system shall be bonded to the grounding electrode system. This includes exterior as well as interior metal gas piping.
What to me appears to be a conflict between these two sections may be rectified in the 2002 edition of the NECA proposal to delete from Section 250-2 the words “that are likely to become energized.” This was submitted as a proposal and accepted by Code-Making Panel No. 5. We will have to wait and see if this proposal survives the code-making process and becomes a part of the 2002 Code.
QUESTION: You said in one of your CQD answers that the gas piping system should be bonded to the electrical supply system grounded conductor. I believe you should have said bonded to the grounding conductor. There is a difference. The 1999 NEC Handbook Section 250-104(b) says that it should be bonded to the grounding electrode system. What does all this really mean?
ANSWER: Yes, I said metal gas piping should be bonded to the supply system grounded conductor. The supply system grounded conductor is the conductor that is intentionally grounded. The supply system grounded conductor is terminated at the neutral bar in the service equipment and is intentionally grounded by means of the main bonding jumper, which is the screw with the green head or the jumper that connects the neutral bar to the equipments metal frame or enclosure. This is not the grounding conductor as you suggest. The grounding conductor is the one used to connect noncurrent-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode, or both, at the service equipment or at the source of a separately derived system.
Section 250-104(b) does require that metal gas piping should be bonded to the grounding electrode system. This can be done by terminating at the neutral bar, or any of the electrodes in the grounding electrode system. It is important to understand that Section 250-52(a) does not permit a metal underground gas piping system to be used as a grounding electrode.
QUESTION: When I bond to a gas pipe am I grounding it? If so, does bonding always mean grounding?
ANSWER: I would prefer saying that you bond a gas pipe to something rather than saying you bond something to a gas pipe. Article 100 defines bonding as “the permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed.” Bonding does not always mean grounding. Metallic parts used in or at a swimming pool are bonded together to form a common bonding grid but, there is no requirement that the common bonding grid be connected to any grounded or grounding conductor.
Conclusion: Natural gas and electricity don’t mix. A gas leak in conjunction an electrical spark may be fatal but if we inadvertently energize a metal gas pipe that has not been grounded, then we may electrocute someone who touches that gas pipe and a grounded surface. So choose your poison, I prefer the grounding of metal gas pipes.
TROUT is a technical consultant for Maron Electric Company of Chicago, and he is chairman of the National Electrical Code-Making Panel 12, representing NECA. He is also the principal author of Electrical Contractor
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