Okay, let's break down this grounding electrode conductor (GEC) situation for your 400A 3-phase 480V service, and address the AHJ's request. Your proposed solution is generally acceptable, BUT it requires careful consideration of code compliance.Here's the analysis, addressing each part of your proposal

Understanding the Basics (Key Concepts)
Grounding Electrode System (GES)

This is the entire assembly of grounding electrodes (ground rods, Ufer, building steel, etc.) and the conductors connecting them together. It's what ties the electrical system to the earth.

Grounding Electrode Conductor (GEC)

This is the conductor that connects the service equipment (neutral bus) to the grounding electrode system. It's a critical safety element.

Service Equipment

This is typically the service disconnect, but in your case, the meter can also be considered part of the service equipment since the service conductors terminate there.

Neutral-to-Case Bond (Service Bonding Jumper)

This is the connection that ties the neutral conductor to the service equipment enclosure (metal can). This ensures that fault current has a low impedance path back to the source, facilitating the operation of overcurrent protective devices.

Analyzing Your Proposal

You propose the following:1. Ground Rod GEC to Meter Can Neutral

Terminate the GEC from your ground rods to the neutral bar in the meter can (which is factory-bonded to the can).2.

Building Grounding System GEC to Service Disconnect Neutral

Terminate the GEC from the building's main ground bar (Ufer, fire sprinkler, step-down transformers, etc.) to the service disconnect neutral bar (bonded to the can).

Is it Compliant?

Generally, yes, with caveats. This approach adheres to the intent of the NEC for creating a robust grounding system. Here's a breakdown: Acceptability of Meter Can Termination

The AHJ's requirement for a GEC termination in the meter can is reasonable. Since the service conductors terminate there, it's a valid location for establishing a grounding connection. The fact that the meter can's neutral is factory-bonded to the enclosure is essential for this approach to work.

Separating GEC Functions

Your plan effectively divides the GEC function. One GEC handles the local ground rods, while the other handles the building's supplementary grounding electrodes. This is acceptable as long as the sizing is correct for each conductor.

Sizing of GECs is CRITICAL

This is where careful attention to the NEC is crucial.

Ground Rod GEC

The GEC connecting the ground rods to the meter can neutral must be sized according to NEC 250.66, based on the size of the unfused service entrance conductors (coming in from the utility). Table 250.66 is used to determine the minimum size. You'll use the conductors before the meter for this calculation. However, note that after you establish a grounding electrode system you do not have to size the GEC larger than a #6 AWG copper conductor to a rod, pipe, or plate electrode.

Building Grounding System GEC

The GEC connecting the building's main ground bar to the service disconnect neutral must also be sized according to NEC 250.66, based on the size of the unfused service entrance conductors. Again, this means using the conductors coming in to the meter. This GEC will connect to the various building electrodes (Ufer, building steel, etc.) connected to your main ground bar.

Important Considerations and Requirements (NEC References) NEC 250.24(C)

This section governs the grounding of separately derived systems. You likely don't have a separately derived system at the service point, but it's worth confirming.

NEC 250.24(A)(1)

This allows the neutral conductor to be connected to a grounding electrode conductor at the service equipment. Your proposal fits within this allowance.

NEC 250.50 Grounding Electrode System. All grounding electrodes as described in 250.52 that are present at each building or structure served shall be bonded together to form the grounding electrode system. NEC 250.53(C)

Deals with supplemental grounding electrodes. This applies if you have multiple ground rods.

NEC 250.64(F)

Grounding Electrode Conductor Connections. You can use irreversible compression connectors, exothermic welding, listed pressure connectors, listed clamps, or other approved means for GEC connections. Ensure all connections are properly made and listed for grounding purposes.

Recommendations1. Verify with AHJ

While your plan is generally compliant, always get written confirmation from the AHJ before proceeding. They might have specific local interpretations.2.

Accurate Sizing

Absolutely ensure the GECs are sized correctly according to NEC 250.66 based on the unfused service entrance conductor size. Oversizing is always better than undersizing.3.

Proper Connections

Use appropriate connectors (listed for grounding) for all GEC terminations. Make sure connections are clean and tight.4.

Documentation

Keep detailed records of your grounding electrode system, including the size and type of GECs, electrode locations, and connection methods. This will be valuable for future maintenance and inspections.5.

Meter socket requirements. Check with the utility company that provides the meter as they may have specific requirements that overrule the NEC.

In Summary

Your proposed approach, of terminating the ground rod GEC in the meter can and the building grounding system GEC in the service disconnect, can be compliant if you meticulously follow the NEC requirements, particularly regarding conductor sizing and proper connections. Confirm with your AHJ, size the GECs correctly, and use appropriate hardware. Good grounding is critical for safety! Flag for review