Short definition
A plastic pipe ground bridge (more formally, a bonding jumper) is a copper conductor — typically #6 AWG for residential service — that bridges a plastic section of metal water or gas piping. Required by NEC 250.104 when a plastic union, filter housing, dielectric union, or PEX splice interrupts otherwise-metal piping, to maintain electrical bonding continuity across the system.
What it is
NEC 250.104(A) requires the metal water piping system in or on a building to be bonded — electrically connected — to the service equipment grounding bus. The point isn’t grounding (a path to earth); it’s bonding (keeping all metal at the same electrical potential), so a fault doesn’t put one part of the metal system at lethal voltage relative to another.
When a plastic component breaks the metal continuity — a plastic-housing whole-house water filter, a dielectric union at the water heater, a PEX repipe section, or a stretch of CPVC — the metal sections on either side are no longer electrically connected. NEC then requires a bonding jumper to bridge the gap and restore continuity.
The conductor is typically #6 AWG copper for a residential 100–200 amp service (per NEC 250.66). Bonding clamps go on the metal pipe upstream and downstream of the plastic component.
The same rule applies to gas piping in NEC 250.104(B) — see CSST.
Why it matters to a homeowner
You’ll see this most often at the water heater (where dielectric unions are common) and after PEX repipes that retain some metal sections. The condition the rule protects against: during an electrical fault, current flows through the metal pipe system to find ground. If the system is fragmented by un-bridged plastic sections, different metal segments end up at different voltages. Someone touching two formerly-bonded metal items — a faucet and a drain, the water heater and the tub — gets shocked through the body during the fault.
Adding a bonding jumper is a cheap, code-compliant fix. The hardware is $20–$50; an electrician adding one during another visit is $100–$200. Standalone, $150–$300.
When you’ll encounter this term
- Installing a whole-house plastic-housing water filter — install bonding jumper at the time of install if the upstream and downstream pipe is metal
- PEX repipe with metal remaining at the water heater or other points — a jumper around the PEX section maintains the original ground path
- Adding a dielectric union at the water heater — jumper required to maintain continuity (the dielectric union is intentionally non-conductive)
- Inspector during electrical work flags missing jumpers as code violations
Common variants and disambiguation
- Bonding jumper across plastic (this term) vs. bonding the whole metal water system to ground (the broader 250.104(A) requirement). The jumper handles a specific gap; the broader requirement is the system-level bond at the panel.
- Bonding (electrical connection between metals) vs. grounding (path to earth). See electrical grounding via water pipe.
- Bond clamp on the water main vs. bond clamp around a plastic filter or dielectric union. Both serve the same continuity purpose; different physical locations.
Common failure modes
- Missing entirely after a PEX repipe. No jumper added; system bonding fragmented.
- Wrong wire size. #14 or #12 used where #6 is required for typical 100–200 amp residential service.
- Corroded clamps. Bonding fails silently after years.
- Clamp on painted pipe. Paint isolates the bond; clamp doesn’t make electrical contact.
- Loose set screw. Vibration or settling loosens the clamp over time.
- Confused with grounding electrode. Homeowner thinks the bond is the ground; actually it’s just maintaining continuity. The grounding electrode (rod, Ufer, water pipe) is separate.
Cost data
- Bonding clamp + #6 wire kit: $20–$50.
- Electrician install during another visit: $100–$200.
- Standalone install: $150–$300.
Washington note
Washington adopts the NEC via WAC 296-46B. The bonding rules (NEC 250.104) transfer in by reference. WA L&I requires a licensed electrician for paid bonding work, with an electrical permit for changes to the bonding configuration.
For a homeowner who wants to verify what exists today: at the water heater, look for a copper conductor clamped to the metal pipe upstream of the dielectric union (or unions, hot and cold) and connected to the metal pipe downstream. At a whole-house plastic filter, look for the same — copper jumper from upstream metal pipe to downstream metal pipe. Photograph for your records during routine maintenance.