Bonding Jumper
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Main bonding jumper: what it means for the Texas exam

Bonding Jumper editorial teamSources checked 3 min read

The main bonding jumper is the connection, in the service equipment, between the grounded conductor, usually the neutral, and the equipment grounding conductors and enclosure. It is the one point where the fault path from the building's metal parts joins the conductor that runs back to the utility transformer. It is often a green screw or strap.

Inside a service panel: a neutral bar and a separate equipment grounding bar, with a strap between them labeled main bonding jumper, the incoming neutral from the utility, and a fault arrow running from a metal box onto the grounding bar, through the jumper and back out on the neutral
One bond at the service. Fault current crosses it to get back to the transformer.
Use this diagram

Why it is needed

When a hot conductor touches a grounded metal box, current flows on the equipment grounding conductor back to the panel. To reach the source and complete the circuit, it has to cross onto the neutral, which runs back to the utility transformer. The main bonding jumper is that crossing. Without it, the fault current would have only the earth to return through, the current would be too small, and the breaker would not trip. See bonding vs grounding.

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Only once

The neutral and the equipment grounding system are joined at the service and, for a separately derived system such as a transformer, at that system by its own system bonding jumper. They are not joined again downstream. In a subpanel the neutral bar floats, isolated from the enclosure, and the equipment grounds land on a separate bar. If the two were bonded in a subpanel, normal neutral current would split onto the equipment grounding conductors, raceways and enclosures, putting current on metal people touch.

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Sizing

The main bonding jumper is sized under 250.102 from the size of the service conductors, not from Table 250.122. A manufacturer's screw or strap supplied with listed service equipment is the usual form. Our grounding electrode conductor sizing guide shows how the sizing tables differ.

  • System bonding jumper. The same job at a separately derived system.
  • Equipment bonding jumper. Joins parts of the equipment grounding path, for example around a flexible fitting.
  • Supply-side bonding jumper. Bonds metal parts on the line side of the service disconnect.

Common mix-ups

  • Bonding the neutral in a subpanel. It belongs only at the service or derived system.
  • Thinking the jumper is the GEC. The grounding electrode conductor runs to the electrode; the main bonding jumper stays inside the equipment.
  • Removing the green screw at the service. That breaks the fault path.
  • Calling the neutral a ground. It is the grounded conductor and carries current every day. See neutral conductor.

On the Texas journeyman exam

The main bonding jumper sits in the services, service equipment and separately derived systems area, 10 scored items across both portions under the PSI bulletin. Study to say where the bond goes, why it is not repeated, and which section sizes it.

Practice it

Every term in this set is in the electrical terms glossary.

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Not affiliated with or endorsed by TDLR, PSI or NFPA. NEC and National Electrical Code are registered trademarks of NFPA.

Sources

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Facts checked 26 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.

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