GEC and EGC are two of the most commonly confused abbreviations in the NEC. They're both "grounding conductors," they're often discussed in the same breath, and they're sized from two completely different tables. Mixing them up is an easy way to misread a code requirement.
GEC: Grounding Electrode Conductor
The grounding electrode conductor (GEC) is the conductor that bonds your electrical service to the grounding electrode system — ground rods, a metal water pipe, or a concrete-encased electrode. The required GEC size scales with the size of your service-entrance conductors, not your panel's amperage rating directly, and its minimum size comes from NEC Table 250.66.
Table 250.66 also caps GEC size for specific electrode types regardless of how large the service is: rod, pipe, or plate electrodes never require larger than 6 AWG copper (250.66(A)), and concrete-encased electrodes never require larger than 4 AWG copper (250.66(B)).
EGC: Equipment Grounding Conductor
The equipment grounding conductor (EGC) does a different job. It connects the metal frames and enclosures of electrical equipment — panels, motors, appliance housings — back to the system so that a fault current has a low-impedance path to trip the breaker, rather than energizing the equipment's metal parts and creating a shock hazard. EGC sizing is governed by NEC Table 250.122, and unlike the GEC, it is based on the rating of the circuit's overcurrent device (the breaker or fuse), not on the service-entrance conductor size.
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Look up the minimum GEC size for your service-entrance conductor size.
The Core Difference, Side by Side
| Aspect | GEC | EGC |
|---|---|---|
| Connects | Service to the grounding electrode (ground rod, water pipe, concrete-encased electrode) | Equipment metal frames/enclosures back to the system |
| Sized from | NEC Table 250.66, based on service-entrance conductor size | NEC Table 250.122, based on the overcurrent device rating |
| Size caps | 6 AWG copper max for rod/pipe/plate electrodes; 4 AWG copper max for concrete-encased electrodes | No blanket cap — scales with breaker size per Table 250.122 |
How to Read NEC Table 250.66 for the GEC
Find your service-entrance conductor size (copper or aluminum) in the table's left columns, then read across to find the minimum required GEC size. For example, 2 AWG through 1/0 AWG copper service conductors require a 6 AWG copper GEC; 250 kcmil through 500 kcmil copper service conductors require a 2/0 AWG copper GEC. GEC size is based on the size of the service-entrance (or largest ungrounded) conductors, not the panel's amp rating directly — two services rated at the same amperage can require different GEC sizes if they use different conductor sizes to achieve that rating.
Why the Distinction Matters
- They use different tables: Looking up an EGC size in Table 250.66, or a GEC size in Table 250.122, will give you the wrong answer.
- They're driven by different inputs: GEC size follows the service-entrance conductor size; EGC size follows the branch or feeder overcurrent device rating.
- The GEC has hard caps that the EGC doesn't: A rod/pipe/plate electrode GEC never exceeds 6 AWG copper, and a concrete-encased electrode GEC never exceeds 4 AWG copper — the EGC has no equivalent blanket cap.
- Both are required, and both do different safety jobs: The GEC ties the system to earth; the EGC gives a fault path back to the source so the breaker trips.
Frequently Asked Questions
Q: What is a grounding electrode conductor (GEC)?
A: The grounding electrode conductor (GEC) is the conductor that bonds your electrical service to the grounding electrode system — ground rods, a metal water pipe, or a concrete-encased electrode. Its minimum size is set by NEC Table 250.66, based on the size of your service-entrance conductors.
Q: What is an equipment grounding conductor (EGC)?
A: The equipment grounding conductor (EGC) is the conductor that connects the metal frames and enclosures of electrical equipment back to the system so a fault current has a path to trip the breaker, rather than energizing the equipment's metal parts. EGC sizing is governed by NEC Table 250.122, based on the rating of the circuit's overcurrent device.
Q: How do I read NEC Table 250.66?
A: Find your service-entrance conductor size (copper or aluminum) in the table's left columns, then read across to find the minimum required grounding electrode conductor (GEC) size. For example, 2 AWG through 1/0 AWG copper service conductors require a 6 AWG copper GEC; 250 kcmil through 500 kcmil copper service conductors require a 2/0 AWG copper GEC.
Q: Why is my GEC smaller than expected for a large service?
A: Table 250.66 includes size caps for specific electrode types. A GEC connecting only to rod, pipe, or plate electrodes is never required to be larger than 6 AWG copper, even on very large services, per NEC 250.66(A). A GEC to a concrete-encased electrode is capped at 4 AWG copper per 250.66(B).
Q: Does GEC size depend on panel amperage or wire size?
A: GEC size is based on the size of the service-entrance (or largest ungrounded) conductors, not the panel's amp rating directly. Two services rated the same amperage can require different GEC sizes if they use different conductor sizes to achieve that rating.
Disclaimer: While our articles and tools are designed to align with the National Electrical Code, always check with local building inspectors and licensed electrical contractors before initiating physical installations.