Grounding Electrode Conductor Sizing

Grounding & BondingNEC 2023CEC Equivalent: CEC Rule 10-114

The grounding electrode conductor is the wire that bonds your electrical system to the earth through a grounding electrode. It needs to be large enough to handle the fault currents that might flow through it during a ground fault, but it also does not need to be excessively oversized because its job is different from a circuit conductor. Table 250.66 correlates the GEC size directly to the service-entrance conductor size. For example, if your largest service conductor is 2 AWG copper, the GEC must be at least 8 AWG copper. If the service uses 500 kcmil copper, the GEC must be at least 1/0 AWG copper. For parallel service conductors, you add up the total circular mil area to find the equivalent single-conductor size. There are also practical exceptions that cap the minimum GEC size for certain electrode types: a GEC to a ground rod, pipe, or plate electrode never needs to be larger than 6 AWG copper, and a GEC to a concrete-encased (Ufer) electrode never needs to be larger than 4 AWG copper.

When You Need This

Installing or upgrading a service entrance and need to select the correct GEC wire size
Running a GEC to a ground rod on a new residential construction project
Connecting to a Ufer (concrete-encased) electrode on a new commercial building foundation
Answering exam questions about grounding electrode conductor sizing — Table 250.66 is a common reference

Key Points

1GEC size is based on the largest ungrounded service-entrance conductor size, not on the load

2For parallel service conductors, add the circular mil areas to find the equivalent single-conductor size

3GEC to a ground rod, pipe, or plate: maximum required size is 6 AWG copper (or 4 AWG aluminum)

4GEC to a concrete-encased (Ufer) electrode: maximum required size is 4 AWG copper

5GEC to a ground ring: sized per the full table without the electrode-type exceptions

6Copper and aluminum columns are provided — aluminum GECs are permitted but must be two sizes larger than copper

7The GEC must be one continuous length without splices, unless using irreversible compression connectors or exothermic welding

Common Mistakes

Oversizing the GEC to a ground rod — it never needs to be larger than 6 AWG copper per 250.66(A)

Running an undersized GEC by using the electrode-type exception when the electrode type does not qualify for it

Splicing the GEC with improper methods — only irreversible compression connectors or exothermic welds are allowed

Confusing the GEC (Table 250.66) with the equipment grounding conductor (Table 250.122) — they are different wires with different sizing rules

Forgetting to add parallel service conductor areas before looking up the table — each parallel set must be combined

Exam Tip

Know the two key exceptions: ground rod = 6 AWG copper max, Ufer = 4 AWG copper max. The exam loves to give you a large service and then ask for the GEC size to a ground rod — the answer is always 6 AWG copper, no matter how big the service is.

Frequently Asked Questions

The GEC (sized by Table 250.66) connects the service neutral or equipment to the grounding electrode (earth connection). The EGC (sized by Table 250.122) runs with the circuit conductors and provides a fault return path from equipment back to the source. They have different purposes and different sizing rules.

Yes, Table 250.66 includes an aluminum column. However, aluminum must not be in direct contact with the earth or concrete, so it cannot be used for the portion of the GEC that runs to a ground rod or a concrete-encased electrode.

Inline Tools

Grounding Calculator

Size grounding electrode conductors per NEC 250

Related Code Sections

250.122Equipment Grounding Conductor Sizing 310.16Ampacity of Insulated 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.