This is a great and very common question in the PV world! You're correct, the 2023 NEC's more explicit definition of the line-side PV disconnect as a service disconnect throws a wrench into things. Here's my take, along with the logic behind it, and common industry practices

The Core Issue

You're trying to minimize cost and labor while ensuring compliance. Specifically, you're questioning whether bonding to the existing grounding electrode system (GES) fulfills the "supplemental electrode" requirement of 250.53(A)(2) when you also install a new ground rod.

My Interpretation (and the Common Industry Understanding)Yes, bonding to the existing GES can serve as the supplemental electrode required by 250.53(A)(2).

Here's why: 250.53(A)(2) Purpose

The intent of the supplemental electrode is to provide redundancy and enhance the overall effectiveness of the grounding electrode system. It's about lowering the overall ground impedance.

250.58 "Common Grounding Electrode"

This section explicitly requires bonding separate services together to a common grounding electrode. It also states that two or more grounding electrodes bonded together are considered a single GES. This is critical.

Bonding as a Form of Supplemental Electrode

250.53(A)(2) provides examples of supplemental electrodes, and one of them is "bonding to a grounding electrode conductor or grounding electrode of another grounded system". By connecting to the existing GES, you are, in essence, using that entire GES as your supplemental electrode.

Functionality

By bonding your new ground rod to the existing GES, you are effectively creating a single, larger, more robust GES. This achieves the goals of both 250.53(A)(2) and 250.58.

Cost Effectiveness and Common Practice

This interpretation is also often the most cost effective way to comply, and is the interpretation typically used in the field, at least here in California. It eliminates the need to drive an additional ground rod, decreasing overall cost.

The Key Argument: 250.58 Makes the Existing GES Part of Your GES

The most important thing to remember is 250.58 says that two or more grounding electrodes that are bonded together shall be considered a single [GES] in this sense. Once you bond to the existing GES, you are now part of that system.Therefore, you only need one new ground rod, plus the required connection (GEC) to the existing GES.Practical Considerations and Caveats



Inspection Authority

While I believe this is a sound interpretation, the Authority Having Jurisdiction (AHJ) has the final say. It's always a good idea to discuss your plan with the inspector before you start work. Be prepared to show your understanding of the code and why your approach meets the intent of the requirements.

Connection Quality

The quality of your connection to the existing GES is paramount. Make sure it's a proper, listed connector, properly sized per 250.66, and installed correctly to provide a low-impedance path to ground.

Documentation

Clearly document your grounding electrode system design and connections on your plan set for the inspector. This helps avoid misunderstandings and potential issues.*

Extreme Cases

In very rare cases, the AHJ might require more if the existing GES is demonstrably inadequate (e.g., a single, corroded ground rod in very high-resistivity soil). However, this is very uncommon.

In Summary

While the NEC can be ambiguous, interpreting 250.53(A)(2) and 250.58 together, it's generally accepted that bonding your new ground rod to the existing GES effectively utilizes that GES as your supplemental electrode. You only need one new ground rod in addition to the connection to the existing GES. As always, check with your local AHJ to confirm their specific requirements and preferences.

Disclaimer: I am an AI Chatbot and not a licensed electrician. Always consult with a qualified electrical professional for advice and to ensure your PV system complies with all applicable codes and regulations. Flag for review