How to Size a Grounding Electrode Conductor (GEC)?

How to Size a Grounding Electrode Conductor (GEC)?

Let’s break it down in detail based on the National Electrical Code (NEC), particularly NEC Article 250, which governs grounding and bonding.

What is a Grounding Electrode Conductor (GEC)?

A Grounding Electrode Conductor (GEC) is the wire that connects the grounding system of an electrical installation (typically the main service panel or equipment) to the grounding electrode, such as a ground rod, ground plate, or building steel. The purpose is to safely dissipate fault currents and lightning surges into the earth.

Why Is Sizing Important?

The GEC must be properly sized to:

- Withstand available fault current

- Ensure safety and compliance

- Protect electrical systems and equipment

How to Size a GEC?

1. Determine the Size of the Largest Ungrounded Service-Entrance Conductor or Equivalent

This means you first look at the size of the service conductors (hot wires) entering the building.

2. Refer to NEC Table 250.66

This table is used to determine the minimum size of the GEC, based on the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors.

Here’s a simplified version:

Note: Aluminum GECs must be one size larger than copper.

Special Considerations:

If Connecting to a Ground Rod Only (Rod, Pipe, or Plate Electrodes):

NEC 250.66(A) allows the conductor to be no smaller than 6 AWG copper or 4 AWG aluminum, regardless of service size. That's because the resistance of the ground rod limits current flow, making larger wires unnecessary.

Multiple Grounding Electrodes:

If multiple grounding electrodes are used (like rods and rebar), you still only need to size the GEC based on the largest conductor entering the building—not the total combined grounding electrode area.

Conductors in Parallel:

If you have conductors in parallel, you add the cross-sectional areas to determine equivalent size, and then refer to Table 250.66.

Example:

Let’s say your service-entrance conductors are 3/0 AWG copper.

According to NEC Table 250.66, the GEC must be at least 4 AWG copper.

But if you're just connecting to a ground rod, you can use 6 AWG copper, even if your service is large.

Visual Breakdown (based on the image):

Grounding Rod: The metal rod driven into the earth to make an electrical connection with the ground.

Grounding Electrode Conductor (GEC): The wire connecting your electrical system to the grounding rod.

Proper clamping and secure connection are essential for continuity and safety.