Grounding and Bonding at the Electrical Service:
Ground Rods, Water Pipes, Gas Lines and the Bonding Jumper

What grounding and bonding do

They’re two different jobs that use similar-looking wire.

Grounding connects the electrical system to the earth. Ground rods driven into the soil, a buried metal water pipe, or steel in the foundation concrete do that. The earth connection helps with lightning and power surges and keeps the system’s voltage steady relative to the ground.

Bonding connects metal things together: the panel, the metal water pipes, the gas piping and other metal piping. If a live wire touches a bonded pipe, the fault current has a low-resistance path back to the panel, and the breaker trips. Without bonding, the pipe can sit energized with nothing tripping, waiting for someone to touch it and a faucet at the same time.

The main bonding jumper is where the two systems meet. At the main service panel (and only there), the neutral and the ground are tied together. In a subpanel they’re kept separate. A Gladstone basement subpanel had the neutral and ground bonded together, and the same panel used a painted deck screw as its grounding screw. Subpanels get their own post later; the short version is that the neutral-to-ground connection belongs at the main service.

Ground rods and the grounding electrode conductor

The heavy bare copper wire that runs from the panel or meter to a ground rod is the grounding electrode conductor. Russ looks for it at the service and follows it where it’s visible.

The National Electrical Code, adopted with amendments in both Oregon and Washington, generally calls for a single ground rod to be backed up by a second electrode, usually a second rod at least 6 feet away, unless the one rod is shown to meet a resistance limit. Many older Portland-area houses have one visible rod. Some have none visible at all, which may mean it’s buried, or that the house relies on the water pipe.

The failures Russ wrote up were physical. A Portland property had a ground rod with a clamp on it and no wire running to it. Another Portland rod stuck up above the soil where a mower or a shovel could hit it. In Gresham, the ground wire was damaged and left exposed to more damage.

The water pipe ground and the repipe problem

For decades, the metal water line coming into the house served as a grounding electrode, and the electrical code still treats buried metal water pipe as one (it has to be supplemented by another electrode). That works as long as the pipe is metal all the way into the ground.

Repiping breaks it. When the old galvanized or copper line is replaced with PEX or other plastic, the ground clamp often stays on a short piece of copper that no longer goes anywhere. In one Portland house, the service appeared to use the original metal water pipes as its grounding electrode, and the house had since been repiped. In a Vancouver house, a ground clamp that may have been on the old water line was connected to nothing. A Lake Oswego report found a bonding jumper disconnected and hanging loose near the water heater.

The water heater jumper is its own small item. A short wire with a clamp on each end that bridges the hot and cold pipes at the water heater keeps the metal piping on both sides bonded, because the water heater’s fittings and dielectric unions can break that path.

Gas piping and CSST

Metal gas piping gets bonded too, so a fault onto a gas pipe trips a breaker. The most common finding in this whole group was a gas bonding clamp installed over paint. The electrical code calls for paint and other nonconductive coatings to be removed where a grounding or bonding connection is made. A clamp over paint may not make solid contact. Russ found this in about 10 houses, from Ridgefield and Vancouver to Tigard and Gresham.

Rust on the gas piping and meters with no protection from cars are the other common findings there. The post on rust on gas pipes and unprotected gas meters covers them.

Missing bonds came up too. A Springfield house had no visible bonding jumper at the gas meter, and a Clackamas house had the gas bonding wire disconnected and hanging.

CSST is the yellow or black flexible gas tubing common in houses built or remodeled since the 1990s. Its manufacturers require it to be bonded directly to the electrical system, because lightning striking nearby can arc through thin tubing that isn’t bonded and puncture it. Russ notes CSST when he sees it and looks for the bonding clamp. When he can’t find one, the report recommends an electrician or gas fitter confirm it.

What a home inspection can and can’t see

Russ looks at the visible grounding and bonding connections: the grounding electrode conductor at the panel and meter, any ground rods above grade, clamps on water pipes and at the water heater, bonding at the gas meter and gas piping, and the neutral and ground arrangement inside the panel when the cover is removed. He tests a representative number of outlets with a tester, which shows whether an outlet has a ground path. The posts on two-prong outlets and GFCI protection cover what those outlet results mean.

He doesn’t measure ground rod resistance, dig for buried rods or trace wiring inside walls. When a connection is missing, loose, on paint or connected to nothing, the report recommends a licensed electrician evaluate the grounding and bonding system. A house with a pool or hot tub has a separate set of bonding rules, covered in the post on pool bonding.

Older panels add their own grounding questions, and the post on fuse boxes in older homes covers one of them. To set up an inspection, you can book online.