You're touching on a common point of confusion and a potential area of misinterpretation. Let's break it down: GEC (Grounding Electrode Conductor)

This connects the service equipment (like the main panel) to the grounding electrode system (like a ground rod or water pipe).

EGC (Equipment Grounding Conductor)

This runs with the circuit conductors (hot and neutral) to ground non-current carrying metal parts of equipment (outlets, appliances, etc.) back to the service.You're quoting

250.122, which specifically addresses Equipment Grounding Conductors (EGCs), not Grounding Electrode Conductors (GECs). 250.122 is about the size of the ground wire in a circuit. This section dictates the minimum size of the EGC based on the rating of the overcurrent protective device (circuit breaker or fuse) protecting the circuit. If the OCPD is rated to 30A, the EGC must be at least #12 AWG copper.

Grounding Electrode Conductors (GECs) are covered by 250.66. This section outlines the minimum size of the GEC based on the size of the service entrance conductors.

Key Differences and Why it Matters



Purpose

GECs and EGCs serve different purposes in the electrical system. The GEC grounds the system, while the EGC grounds equipment.

Sizing

The sizing rules are different and based on different criteria.

Consequences

Using an undersized GEC can compromise the overall grounding of the electrical system, potentially increasing the risk of shock or fire. Using an undersized EGC can compromise equipment grounding, increasing the risk of shock.

So, is a #12 GEC legal for a 30A service? NO. Section 250.122 refers to EGCs, not GECs. The size of the GEC depends on the size of the service entrance conductors. You have to reference 250.66 for the proper sizing. For example, if you have 2/0 copper service entrance conductors (typical for 200A service), you'd need a #6 copper GEC to a ground rod, and a #4 copper to a water pipe.

Why the Inspector Might be Harassing Your Guy



Confusion

The inspector might be confusing the GEC with the EGC or vice versa.

Misunderstanding of 250.66

Your guy might be incorrectly applying 250.122 to the GEC.

Local Amendments

Some jurisdictions have local amendments to the NEC that are stricter than the national code. It's always important to check for local variations.*

Not enough information

The inspector may not have been provided with enough information to determine proper sizing.

What to Do


Clarify

Politely clarify the distinction between GECs and EGCs with the inspector. Ensure that all assumptions are correct.2.

Refer to 250.66

Show the inspector the relevant table (250.66) and explain how you determined the GEC size based on the service entrance conductor size.
3.

Check Local Amendments

Research local amendments to the NEC in your jurisdiction.4.

Escalate (If Necessary)

If you believe the inspector is incorrect and is misinterpreting the code, you may need to escalate the issue to a higher authority within the inspection department.

In Summary:

Don't confuse 250.122 (EGCs) with 250.66 (GECs). The #12 THHN wire is acceptable for the EGC when the OCPD (overcurrent protective device) is rated to 30A or less. You must size the GEC to 250.66, which is based on the size of the service entrance conductors, not the OCPD rating. Flag for review