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Building Code Reference

Got a CEC 250.104 correction?

Gas water pipe bonding

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CEC 250.104 requires that all metal water piping and metal gas piping in a building be bonded to the electrical grounding system. A bonding jumper connects those metal pipes to the grounding electrode conductor, the neutral conductor at the service, or the equipment grounding bus in the main panel. This keeps the piping at the same electrical potential as the grounding system — so if a fault energizes the pipe, the current has a path back to the source and the breaker trips instead of the pipe becoming a shock hazard. Residential and commercial permits commonly get flagged on 250.104 when the bonding jumper isn't called out on the electrical or plumbing plan sheets.

How to fix it

  1. Identify every metal pipe run that needs bonding

    Walk the gas and water piping systems on your plans. Any metallic water piping (including cold-water supply, hot-water supply, and recirculation loops) and any metallic gas piping must be bonded. This includes gas lines to appliances, BBQ stubs, and fireplace branches. Plastic or PEX piping does not require a 250.104 bond, but any metal stub-outs or valves connected to plastic supply lines may still need to be bonded if they're capable of becoming energized.

  2. Size the bonding jumper per Table 250.102(C)(1)

    CEC 250.104(A)(1) requires sizing the water pipe bonding jumper using Table 250.102(C)(1), based on the size of the largest ungrounded service-entrance conductor. For a 200A service with 2/0 AWG copper service conductors, that table requires a 4 AWG copper bonding jumper. For a 100A service with 4 AWG copper conductors, an 8 AWG copper bonding jumper is the minimum. Gas piping is bonded under 250.104(B) with a conductor sized per Table 250.122. Don't write "bonding jumper per code" on your plans — state the actual wire gauge. That's what the plan-checker needs to sign off.

  3. Mark the bonding attachment point on the electrical plan

    Show where the bonding jumper lands. Acceptable connection points include: the grounding electrode conductor, the grounded service conductor (neutral) at the service entrance, or the equipment grounding bus in the main panel. The plan-checker needs to see both ends of the bonding jumper — where it clamps to the pipe and where it terminates in the panel or on the GEC. Add a leader note on the electrical panel elevation or riser diagram pointing to the bonding connection.

  4. Add a bonding note to the plumbing plan as well

    Don't rely on the electrical plan alone. On the plumbing plan, mark the location where the bonding clamp attaches to the water pipe and the gas pipe. The preferred attachment point is on accessible piping, within 5 feet of where the pipe enters the structure from the meter or street, before any branch points. Note the clamp type (listed bonding clamp, not a hose clamp or wire nut). Plan-checkers cross-reference both sheets and will flag a mismatch between the electrical and plumbing plans.

  5. Add separate callouts for gas and water piping

    CEC 250.104(A) covers water piping. CEC 250.104(B) covers gas piping. They're both required, but a plan-checker may call out whichever one is missing if you only show one. Put separate callouts on your plans: one for the water pipe bonding jumper and one for the gas pipe bonding jumper. If they both terminate at the same panel bus, note that clearly. For example: "2 separate bonding jumpers, 4 AWG copper each, both terminate at main panel equipment grounding bus" is the kind of specific note that passes plan check without a follow-up question.

  6. For ADUs, trace the bonding back to the right panel

    If the ADU has its own subpanel, the bonding jumper on the gas and water piping serving the ADU can terminate at the ADU subpanel's equipment grounding bus. Size that bonding jumper under CEC 250.104(A)(2) or (A)(3) for the ADU, not from the main service entrance conductor. Show the full path on the ADU electrical plan: pipe clamp location, wire gauge, and panel termination point.

  7. Confirm the bonding clamp will remain accessible

    The bonding clamp must be a listed fitting and the attachment point must remain accessible after construction is complete. No hose clamps, no field-fabricated lugs, and no concealing the clamp behind drywall without an access panel. If the only feasible pipe location is inside a wall cavity, note an access panel on your plans. Otherwise move the clamp to the utility room, garage, or crawlspace where an inspector can verify it without cutting drywall.

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Why you got flagged

Plan-checkers flag CEC 250.104 most often because the bonding jumper simply doesn't appear anywhere on the submitted plans. The electrical plan shows the service panel, branch circuits, and grounding electrode, but there's no note or detail indicating a bonding jumper from the gas line or cold-water supply to the grounding system. The plumbing plan shows the pipe runs but doesn't reference electrical bonding. Neither sheet mentions it, and the plan-checker has no way to confirm it will be installed.

A second common trigger is that the bonding jumper is shown on one sheet but doesn't meet sizing requirements. CEC 250.104 requires sizing the bonding conductor per Table 250.66 based on the service conductor size — not just a "10 AWG jumper per code" note. If the note doesn't reference the correct table or doesn't specify the conductor size, the plan-checker will flag it for clarification.

Gas service upgrades and water heater replacements are also frequent sources of 250.104 corrections. When a contractor pulls a permit for a gas line extension or a new tankless water heater, the plan-checker reviews the full bonding path. If the existing plans show no bonding jumper on the gas line, the correction letter will call it out and require documentation that the bond exists and meets current code.

ADU projects get hit on this regularly because the accessory unit often has its own subpanel. The 250.104 bond on any metal piping serving the ADU must connect back to the appropriate grounding point. If the electrical plan for the ADU only shows the subpanel feeder and not the bonding jumper on the gas and water piping, the plan-checker flags it.

The official code

California Electrical Code (Title 24, Part 3) — California Building Standards Commission

Read the source →

Common questions

Does CEC 250.104 apply to PEX water piping?
No. CEC 250.104 applies to metal piping systems, not plastic or PEX. If your water supply is all PEX or CPVC from the meter to the fixtures, there's no 250.104 bonding requirement on those plastic runs. That said, if you have metal stub-outs, a metal water heater tank, or metal ball valves inline with plastic tubing, those metal sections can still become energized during a fault. Ask your inspector whether any isolated metal components in an otherwise plastic system need bonding — most OC jurisdictions follow the CEC as adopted without modification for this section, but inspectors may have specific preferences for how isolated metal fittings are handled.
Can the gas pipe and water pipe share one bonding jumper?
No. CEC 250.104(A) covers water piping and 250.104(B) covers gas piping separately. Each requires its own bonding conductor. You can't daisy-chain a single wire from the water pipe to the gas pipe and then to the panel. The plan-checker and field inspector will flag it. Both conductors can terminate on the same equipment grounding bus in the main panel, but they need to be separate runs from each pipe system back to that bus.
What wire size do I need for a 200A service bonding jumper?
For a 200A service with 2/0 AWG copper service-entrance conductors, Table 250.66 in the CEC requires a 4 AWG copper bonding jumper for both the gas and water piping. If your service conductors are aluminum, use the aluminum column in Table 250.66 to look up the required size. State the actual AWG number on your plans rather than writing "per code" — plan-checkers expect to see the specific conductor size called out so they can verify the Table 250.66 calculation without doing it themselves.
Where should the bonding clamp be installed on the pipe?
Attach the bonding clamp on accessible piping, within 5 feet of where the pipe enters the structure from the street or meter, before any branch points. The clamp must be a UL-listed pipe bonding clamp sized to the pipe OD — not a hose clamp or improvised fitting. The connection point must remain accessible after all finish work is done. If the pipe will run inside a wall, plan for an access panel or move the bonding clamp location to an accessible area such as a utility room, crawlspace, or garage before the wall closes.
Do I need a bonding jumper on a water heater replacement permit?
Yes, you may. When you pull a permit for a water heater replacement, the plan-checker and inspector review the gas and water piping connected to the unit. If no bonding jumpers are documented on the submitted plans, you'll get a correction to add them. On a simple water heater permit this is usually fast to resolve: add a callout to the plans showing bonding jumper locations and wire sizes. CrossBeam flags this automatically on water heater permit reviews for $25 before you submit, so you can catch it before the correction letter.
What's the difference between bonding and grounding under CEC 250?
Grounding connects the electrical system to the earth through grounding electrodes such as ground rods, the metal water service pipe used as a grounding electrode, or concrete-encased rebar. Bonding under CEC 250.104 connects metal piping systems to the grounding system so that all metal in the building stays at the same electrical potential. If a fault energizes a gas or water pipe, bonding gives the fault current a low-impedance path back to the panel, which trips the breaker instead of making the pipe a shock hazard. Both grounding and bonding are required by CEC Article 250 and they serve distinct but complementary functions.

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