You're asking a complex question involving several code sections. Let's break it down and address your points.

Key Code Sections



690.47(A) Grounding Electrode System (PV Systems)

This section requires a grounding electrode system to be connected to the PV system equipment grounding conductors and to the grounded conductor if the PV system is grounded.

250.32(A) Grounding Electrode System at a Separately Derived Structure

This section generally requires a grounding electrode system at each detached building or structure supplied by a feeder or branch circuit. There are exceptions.

Article 250 Part III: Grounding Electrode System

Covers the requirements for establishing a grounding electrode system.

Article 250 Part VII: Methods of Equipment Grounding

Deals with how to connect equipment grounding conductors.

Your Scenario: PV on a Boat Dock Roof with Boathouse Subpanel PV array on boat dock roof Boathouse subpanel (no grounding electrode) 4-wire feeder from single-family dwelling (with a compliant grounding electrode system). Already a violation of 250.32(A) (no grounding electrode at the boathouse)Your Question: Does 690.47(A) force upgrading the boathouse grounding when adding the PV system?Analysis

This is where it gets nuanced. Here's a breakdown of my understanding and how I interpret these code sections in your situation:1.

250.32(A) Violation Exists Independent of PV

You've correctly identified that a violation of 250.32(A) already exists. The boathouse subpanel fed by a 4-wire feeder typically requires a grounding electrode. The exceptions in 250.32(B) would need to be carefully evaluated to determine if the exception apply, the most common one is the "single circuit" exception.
2.

690.47(A) and the Interconnection

This is the core of your question. 690.47(A) requires the PV system's equipment grounding conductors to be connected to a grounding electrode system. Your argument is that the PV system is indirectly connected to the house's grounding electrode system through the equipment grounding conductor run back to the main panel.
3.

Different Interpretations & AHJ Authority

Here's where opinions can differ. Some inspectors might argue that because the boathouse lacks a proper grounding electrode system according to 250.32(A), 690.47(A) essentially requires you to bring the boathouse up to code. Their logic is that the PV system MUST be connected to a compliant grounding electrode system, and since the boathouse doesn't have one, you have to install one.

Counter-Argument (Your Position)

You're essentially arguing that the PV system IS connected to a grounding electrode system (the house's), albeit indirectly through the existing circuit. Your perspective is that the addition of the PV system doesn't make the existing electrical system any less compliant than it was before the PV system was installed. You're leveraging the idea that you're not worsening an existing condition. The PV system's ground fault current path is still designed to trip the breaker in the house panel.4.

"Existing Building is No Less Conforming..." Argument

You're referencing a common interpretation that alterations shouldn't make an existing system less compliant. However, the AHJ might argue that the PV system, by its nature of adding generation at the boathouse, necessitates a compliant grounding electrode system at that location.

My Recommendation and Opinion



Conservative Approach

To avoid potential issues and ensure safety, the most conservative approach is to install a grounding electrode system at the boathouse that complies with 250.32(A). This directly addresses the existing 250.32(A) violation and arguably makes the PV system installation more robust. It also simplifies the inspection process.

Consult with the AHJ

This is crucial. Before proceeding with the installation, discuss your proposed approach with the local Authority Having Jurisdiction (AHJ). Explain your reasoning, present your code interpretation, and get their feedback. Their interpretation is the one that ultimately matters.

Consider a Hybrid Approach

If the AHJ is hesitant to accept your approach but wants to avoid a full grounding electrode installation, you could explore options like: Running a separate, dedicated equipment grounding conductor from the PV system to the house's grounding electrode. While this doesn't address the 250.32(A) violation, it provides a more direct path for fault current. Installing a ground rod at the boathouse connected only to the PV system's equipment grounding conductors (not bonded to the boathouse subpanel enclosure). This is a less desirable option and might not satisfy the AHJ.

Document Everything

Regardless of the approach you take, document everything carefully. Keep records of your discussions with the AHJ, the code sections you're relying on, and the rationale for your design decisions.

In summary

While you have a valid argument that the PV system is connected to a grounding electrode system, the lack of a grounding electrode system at the boathouse (a 250.32(A) violation) creates a point of contention. The AHJ might require you to address the 250.32(A) violation as part of the PV system installation, using 690.47(A) as justification.

Clear communication with the AHJ is absolutely essential.Important Considerations



Lightning Protection

A boat dock, especially with a PV array, is potentially vulnerable to lightning strikes. While not directly addressed by the NEC, consider the need for lightning protection.*

Corrosion: Marine environments are extremely corrosive. Use appropriate materials and methods to protect the grounding electrode system and connections from corrosion.I hope this helps you navigate this complex situation. Good luck! Flag for review