Bonding jumper

Grounding and bonding get used as one word on a job site, but they do different jobs. Grounding connects the system to the earth. Bonding ties metal parts to each other so none of them can float at a different voltage than its neighbor. A bonding jumper is the piece of wire or strap that does the tying. Get it wrong and the metal in your house can sit quietly energized instead of tripping a breaker.

The one that matters most is the main bonding jumper, covered by Section E3607.5 of the 2021 International Residential Code. It is unspliced, it lives inside the service enclosure, and it connects the neutral to the metal box and the equipment grounding wires. That bond gets made once. Past the service, every subpanel keeps neutral and ground on separate bars, which is why a detached casita or shop is fed with a four-wire feeder instead of three.

Equipment bonding jumpers are the second family, and they show up wherever metal could become energized. Gas piping is the common one. Pinal County states it plainly in its residential gas bulletin: any above-ground gas piping that can become energized has to be bonded to the electrical service electrode system, and a system containing CSST needs a jumper no smaller than 6 AWG copper, run no more than 75 feet.

Main, system, supply-side and equipment bonding jumpers

The National Electrical Code names four kinds of bonding jumper, and the names trip people up because they sound alike.

• Main bonding jumper (NEC 250.28, IRC E3607.5): the single link between the neutral and the equipment ground at the service. It can be a screw, a strap, a busbar or a wire, and it is sized from the service conductors.
• System bonding jumper (NEC 250.30(A)(1)): the same job for a separately derived system, such as a transformer or some standby generator setups. It goes at the source or at the first disconnect, never both, so normal neutral current does not ride on the ground path.
• Supply-side bonding jumper (NEC 250.102(C)): bonds metal raceways and enclosures on the line side of the service breaker, where nothing yet limits a fault. That is why it is sized from the service conductors using Table 250.102(C)(1), not from a breaker rating.
• Equipment bonding jumper (NEC 250.102 and 250.104): the jumpers past the service that keep metal parts at the same voltage, such as across a fitting that does not conduct well or to metal gas and water piping. The CSST jumper above is one of these.

Which edition of the NEC applies depends on the city or county issuing the permit, so the section numbers can shift slightly between jurisdictions. The four jobs stay the same.

For example, a Cave Creek custom home with a propane range gets both. The electrician makes the main bond in the service panel at rough-in. Then a 6 AWG copper jumper runs from the steel gas pipe past the second-stage regulator back to the ground at the service. Two jumpers, two purposes, and on most jobs two different trades. The main bond is an electrician's item all day. The gas jumper is the one that falls through the crack, because the plumber sets the pipe and the electrician lands the wire.

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