NEC EGC Size Chart: How to Select the Right Equipment Grounding Conductor

An electrician on a commercial job opens the ground wire sizing table and discovers that a 200 A overcurrent device requires a 6 AWG copper equipment grounding conductor (EGC) — even when the phase conductors are oversized. That number does not come from an ampacity table; it comes directly from the EGC size chart in NEC Table 250.122. This distinction is easy to overlook, but it is critical for safe, code-compliant installations.

The EGC is not a current-carrying conductor during normal operation. It exists to carry fault current back to the source so the circuit breaker can trip quickly. Because the breaker’s rating sets the amount of energy the conductor may need to handle, code rules tie the EGC’s minimum size to that rating rather than to the load. In this article, we will break down the EGC size chart, explain how to read it, and connect it to the grounding components you will actually install.

What Is an Equipment Grounding Conductor?

An equipment grounding conductor provides a low-impedance path from the exposed metal parts of electrical equipment back to the service grounded conductor or ground bus. It is the conductor that clears ground faults by enabling the overcurrent protection device to open the circuit. The NEC defines the minimum size in Table 250.122, based on the rating or setting of the automatic overcurrent device in the circuit ahead of the equipment.

The EGC is different from a grounding electrode conductor (GEC), which connects the system to earth electrodes such as grounding rods. The EGC is also different from a grounded neutral conductor. This confusion is common, and mixing them up can lead to undersized conductors and unsafe installations.

EGC vs. GEC: Why the Size Charts Are Not Interchangeable

Many installers mistakenly use the grounding electrode conductor size chart (NEC Table 250.66) for equipment grounding. The two tables serve different purposes:

• EGC (Table 250.122): Sized by the overcurrent device rating. It is the fault-clearing conductor between equipment and the source.
• GEC (Table 250.66): Sized by the size of the largest ungrounded service conductor. It bonds the system to the earth electrode.

An EGC can be larger than a GEC in some installations, and vice versa. Always confirm the application before selecting a conductor from either chart.

EGC Size Chart: NEC Table 250.122

The chart below shows the minimum equipment grounding conductor sizes for copper and aluminum conductors, based on overcurrent protection ratings. This is a simplified version of NEC Table 250.122; always verify against the current adopted edition of your local code.

Notice the logic: higher overcurrent ratings require larger EGCs. The conductor does not need to be sized for the load itself; it needs to survive a ground fault until the breaker operates. A 100 A circuit can use an 8 AWG copper EGC even if the phase conductors are 1 AWG or larger. That surprises many people, but it is correct under NEC 250.122.

How to Apply the EGC Size Chart in Practice

Using the chart is straightforward once you know the branch circuit or feeder overcurrent device rating. Follow these steps on every project:

1. Identify the overcurrent protection rating for the circuit. This is the breaker or fuse protecting the equipment.
2. Locate that rating in the left column of Table 250.122.
3. Choose the correct material column based on whether the EGC is copper or aluminum/copper-clad aluminum.
4. Adjust for conductor upsizing when the phase conductors are increased for voltage drop or other reasons. The EGC must be proportionally upsized in cross-sectional area.
5. Verify installation conditions, including temperature ratings, corrosion resistance, and mechanical protection.

For a 400 A circuit with copper EGCs, the chart gives 3 AWG. But if the phase conductors were upsized from 500 kcmil to 750 kcmil, the EGC would need to be increased in proportion to the change in conductor area. A common rule of thumb is to increase the EGC by the same ratio as the phase conductor area increase. This protects the EGC from experiencing excessive fault-current heating when circuit conductors are larger than the minimum.

Always confirm the actual code rules with the authority having jurisdiction. Local amendments can change or restrict certain sizes, especially for PVC-coated conductors or systems with high available fault current.

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Copper vs. Aluminum Equipment Grounding Conductors

The EGC size chart lists both copper and aluminum conductors. Copper is the traditional choice for its high conductivity, corrosion resistance, and mechanical strength. Aluminum and copper-clad aluminum are lighter and less expensive, but they require larger sizes due to lower conductivity. The chart reflects this difference: an aluminum EGC is typically two AWG sizes larger than copper for the same overcurrent protection.

When selecting aluminum conductors, pay close attention to termination points. Aluminum is more susceptible to oxidation and thermal expansion, so terminals must be rated for aluminum, and an antioxidant compound may be required. For direct burial or wet locations, copper-clad or tinned copper is often specified to reduce galvanic corrosion.

The soil type and environmental conditions matter just as much as the conductor material. In acidic or saline soils, a bare copper EGC may corrode faster than a properly insulated conductor. Many design engineers prefer copper-clad steel grounding rods for earth contact, while using copper for the EGC run to equipment. The combination provides both corrosion resistance and high fault-current capacity.

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Practical Installation and Product Considerations

The EGC size chart provides the minimum cross-sectional area, but a code-compliant installation also requires proper mounting, cold-water pipe bonding, and clean terminations. A loose clamp or undersized connection can turn a correctly sized EGC into a dangerous failure point. When you build a grounding system, match the conductor sizes to the overcurrent protection and use approved clamps and busbars for every splice or tap.

For industrial panels, a tinned copper busbar is often the best way to consolidate several EGCs and avoid clutter. Busbars help keep the installation organized and make it easy to verify conductor sizes during inspections. They also simplify the addition of new circuits in the future.

If your project requires a ground rod to supplement the electrode system, remember that the rod’s size is determined by the GEC table, not the EGC table. The bond between the EGC and the grounding electrode system is just as important as the conductor itself. Use a split-bolt connector or an approved grounding clamp to ensure low resistance and long-term reliability.

Many installers ask whether the EGC needs to be in the same raceway as the phase conductors. Generally, the answer is yes. Keeping the EGC in the same conduit reduces impedance and improves fault-current return. It also prevents magnetic heating in metal raceways. When routing separate, all bends must be long sweeps to avoid insulation damage.

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The EGC size chart is not a suggestion; it is a safety requirement. By sizing the equipment grounding conductor according to the overcurrent device rating, you ensure that fault current has a reliable path to trip the breaker. Taking the time to read the chart correctly, compare copper and aluminum options, and install the conductor with quality fittings will protect both equipment and people.

For a complete grounding system, pair the EGC with the right grounding conductors and rods. Review the grounding conductor selection guide on our site, and if you need deeper guidance on rod installation, our grounding rod guide covers practical steps. Every element of the system works together, and a properly sized EGC is the first line of defense against electrical faults.