I agree Don, the code panel has not made it easy for us when they have subjective rules in the book. since I'm looking at it from the Inspector side, I might lean towards bonding the gas line "just in case" no, not really. I know inspectors who want the I-beam in a residential basement bonded because their are NM cables laying on top of it. I think they are over doing it for sure. I am very comfortable with the bonding offered with the equipment grounding conductor of the branch circuit to the appliance. Even Bob's example of the #18 gauge conductor in the appliance cord. There are tons of NM cable branch circuits out there with reduced EGCs. Hey, it's very common for the EGC to be smaller than the grounded or ungrounded conductors. With a gas fired appliance using solenoids it's possible to energize the gas line and this bonding is necessary. There are very few gas fired appliances that don't use electricity.
