Equipment Grounding Conductor Sizing

Grounding & BondingNEC 2023CEC Equivalent: CEC Rule 10-814

The equipment grounding conductor is not designed to carry normal load current. Its job is to provide a reliable path for fault current to flow back to the source so that the breaker can trip and clear the fault quickly. Because of this fault-clearing role, the EGC is sized based on the overcurrent device that will be tripping, not on the normal load current. You find the OCPD rating in the left column of Table 250.122, and the table tells you the minimum copper or aluminum EGC size. For example, a 20-amp breaker requires at least a 12 AWG copper EGC. A 200-amp breaker requires at least a 6 AWG copper EGC. If you upsize the circuit conductors for voltage drop or other reasons, you must also upsize the EGC proportionally per 250.122(B). For circuits run in multiple parallel raceways, each raceway needs its own full-sized EGC based on the OCPD rating — you cannot split one EGC across multiple raceways.

When You Need This

Selecting the EGC size for any new branch circuit or feeder installation
Upsizing circuit conductors for a long voltage-drop run and need to proportionally increase the EGC
Running parallel feeders and need to place the correct EGC in each raceway
Answering exam questions — EGC sizing from Table 250.122 is a frequent topic

Key Points

1EGC is sized by the OCPD rating, not by conductor ampacity or load current

2Table 250.122 provides minimum sizes for both copper and aluminum EGCs

3If circuit conductors are upsized (for example, for voltage drop), the EGC must be upsized in the same proportion per 250.122(B)

4Each parallel raceway must contain its own full-sized EGC — you cannot split the grounding path

5The EGC can be a wire, a metal raceway, or a combination depending on the installation method

6Common sizes: 15A OCPD = 14 AWG Cu, 20A = 12 AWG Cu, 60A = 10 AWG Cu, 100A = 8 AWG Cu, 200A = 6 AWG Cu

Common Mistakes

Sizing the EGC based on the circuit's load current instead of the OCPD rating

Confusing the EGC (Table 250.122) with the GEC (Table 250.66) — they serve different purposes

Forgetting to upsize the EGC when circuit conductors are increased per 250.122(B)

Running one shared EGC through multiple parallel raceways instead of one EGC per raceway

Using an aluminum EGC in locations where aluminum is not suitable, such as direct earth contact

Exam Tip

The sizing rule is simple: find the OCPD rating, look up the table. But the exam will test the proportional upsizing rule from 250.122(B). If the conductors are doubled in circular mil area for voltage drop, the EGC must also be doubled. Use the ratio of actual conductor area to minimum required conductor area, and multiply the EGC area by the same ratio.

Frequently Asked Questions

The EGC's job is to carry enough fault current to trip the breaker. The breaker rating determines how much fault current is needed to open the circuit, so the EGC must be sized to reliably carry that amount. The normal load current is irrelevant because the EGC only carries current during a fault.

Yes, certain metal raceways (like RMC, IMC, and EMT) are recognized as suitable equipment grounding conductors under 250.118. However, you must ensure all connections and fittings maintain a reliable electrical path throughout the raceway.

Inline Tools

Grounding Calculator

Size grounding electrode conductors per NEC 250

Related Code Sections

250.66Grounding Electrode Conductor Sizing 240.4Protection of Conductors

This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.