4.3 Equipment Grounding Conductors

4.3 Equipment Grounding Conductors

The primary defense against electrical shock and fire caused by ground faults is the equipment grounding conductor (EGC). Unlike the grounded conductor (the neutral), which carries current under normal operating conditions, the EGC is designed to carry current only during abnormal fault conditions. It provides a low-impedance path back to the electrical source (the service panel), forcing the circuit breaker to trip instantly when a hot conductor contacts a metal enclosure. Chapter 39 of the International Residential Code (IRC) defines the strict sizing, installation, and bonding requirements for EGCs.

Sizing the Equipment Grounding Conductor (Table E3908.12)

The size of the EGC is not based on the load of the circuit, but on the rating of the overcurrent protective device (OCPD) — the fuse or circuit breaker — that protects the circuit.

Standard EGC Sizing Rules

IRC Table E3908.12 dictates the minimum size of copper or aluminum equipment grounding conductors based on the circuit breaker or fuse size:

Note: For standard residential branch circuits (15A and 20A), the EGC is typically the same size as the circuit conductors. However, for 30A, 40A, and 60A circuits, a 10 AWG copper EGC is permitted, which may be smaller than the circuit's hot conductors (e.g., a 40A circuit uses 8 AWG hot conductors but only requires a 10 AWG copper EGC).

The Voltage Drop Upsizing Rule

A critical detail that inspectors must watch for is when circuit conductors are upsized to compensate for voltage drop (common in long wire runs to outbuildings or remote equipment).

• If the ungrounded (hot) conductors are increased in size (for example, using 10 AWG instead of 12 AWG on a 20-amp circuit to prevent voltage drop), the EGC must also be upsized proportionally in circular mils.
• Failing to upsize the EGC under these conditions is a common code violation, as a smaller EGC might not provide a sufficiently low-impedance path over the longer distance to trip the breaker.

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Installation and Identification of EGCs

EGCs must be installed within the same cable, raceway, or trench as the circuit conductors (hot and neutral). This ensures that the electromagnetic fields of the conductors cancel each other out, keeping the circuit impedance as low as possible during a fault.

• Identification: EGCs must be easily identifiable. They can be bare, covered with green insulation, or green insulation with one or more yellow stripes.
• Splicing: All EGCs entering a junction or outlet box must be spliced together using approved wire connectors (such as wire nuts) to maintain a continuous grounding path, even if the device itself is removed.

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Bonding at Metal Enclosures (E3908.13)

When a circuit enters a metal box or cabinet, the enclosure itself must be bonded to the EGC. This ensures that if a loose hot wire contacts the metal box, the box becomes grounded and trips the breaker, rather than remaining energized and posing a shock hazard.

Approved Bonding Methods

The connection between the EGC and the metal box must be made using secure mechanical fittings:

• Grounding Screws: The box must be tapped to accept a machine screw, and the grounding screw must be used for no other purpose. The screw must be green and have at least two machine threads engaged in the box.
• Grounding Clips: A listed grounding clip can be used to secure the bare grounding wire directly to the sheet metal edge of the box.
• Prohibited Fasteners: The use of drywall screws, wood screws, or standard sheet metal screws to connect grounding wires is strictly prohibited. These fasteners lack the necessary thread engagement, durability, and electrical contact surface to guarantee a low-resistance path over time.

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Grounding of Receptacles and Switches (E4002.2)

Receptacles and switches must have their grounding terminals connected to the EGC. This ensures that the faceplates and any plugged-in appliances are safely grounded.

Self-Grounding Receptacles

Typically, a green bonding jumper must connect the receptacle's grounding screw to the box and the EGC. However, there is an exception for self-grounding receptacles:

• A self-grounding receptacle features a small spring-steel clip on its mounting yoke.
• When installed in a surface-mounted metal box where there is direct metal-to-metal contact between the box and the receptacle yoke (without paper washers or drywall in between), the clip establishes a grounding path, and a separate bonding jumper is not required.
• This exception does not apply to flush-mounted boxes installed behind drywall, where the yoke rests against the drywall rather than the metal box frame.

Grounding of Switches (E4003.2)

Snap switches (light switches) must also be grounded. A grounding wire must be connected to the green grounding screw on the switch yoke, unless the switch is mounted to a grounded metal box using metal screws, which establishes a mechanical grounding connection.