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Q.As a building inspector, I understand Article 250 of the most recent National Electrical Code (2005 NEC) to mean that any potential grounding electrodes available to each electrical service must be bonded together into that service's grounding electrode system. But the code also says that an underground gas piping system may not be used as a grounding electrode. Some of my colleagues believe this means that gas pipes should not be bonded to the water pipes, while I believe that they should be. Who is right?

A.George Flach, former chief electrical inspector for New Orleans, responds: Gas pipes often supply equipment and appliances that are also powered electrically — such as gas-electric central heating furnaces and gas heaters with pumps used for warming water in swimming pools, or gas clothes dryers and gas ranges with illuminated ovens and spark igniters — and they may become energized by the branch circuits that power these units.

To reduce that risk, Section 250.104(B) of the 2005 NEC requires that all gas pipe be bonded. However, the NEC also recognizes the equipment grounding conductor of each branch circuit as a bonding means for the gas piping, and requires no additional bonding or grounding.

Still, there's no reason gas pipes can't be bonded to the water pipes. Gas utility companies usually equip their underground metal gas distribution systems with cathodic protection, typically with an isolation coupling or union at each customer's gas-pipe connection. Grounding and bonding of the customer-owned gas piping system won't interfere with this cathodic protection. And as the note following NEC 250.104(B) emphasizes, it's always a good idea to bond all metal piping and metal air ducts.

There are no changes to 250.104(B) in the pending edition of the 2008 NEC.