NEC 690.41 Grounding for Solar PV Systems: Equipment & System Bonding Guide

Grounding is one of the most misunderstood aspects of solar PV installation — and one of the most frequently flagged during AHJ inspections. NEC 690.41 sets the requirements for ground fault protection in PV systems, while 690.43 and 250.122 cover equipment grounding and EGC sizing.

The shift from grounded to ungrounded (transformerless) inverters changed the grounding picture significantly. Modern string inverters don’t connect either PV conductor to ground — they achieve safety through isolation monitoring instead. Understanding which type of system you’re installing determines what the code requires.

Ground Fault Protection: The Core Requirement

NEC 690.41(A) requires that all solar PV systems have ground fault protection — a mechanism to detect when a fault current is flowing through an unintended path to ground and interrupt it to prevent fire or electrocution.

Ungrounded Systems (Transformerless Inverters)

For modern transformerless inverters:

• No conductor is intentionally grounded
• The inverter continuously monitors the isolation resistance between the PV array and ground
• If isolation drops below a threshold (indicating a ground fault), the inverter shuts down and displays a fault code
• This isolation monitoring function is part of the UL 1741 listing for transformerless inverters

The installer’s responsibility:

• Verify the inverter is listed for ungrounded PV systems (the datasheet or UL certificate will state this)
• Do not accidentally ground either PV conductor — route EGC separately from the PV source circuit conductors and do not confuse the EGC with the negative conductor
• Ensure the inverter’s isolation monitoring is functioning (verified during commissioning)

Grounded Systems (With Isolation Transformer)

For systems with isolation transformers (less common in modern residential/commercial installations):

• One conductor is intentionally grounded through a Ground Fault Protection Device (GFPD)
• The GFPD monitors current in the grounded conductor
• A fault is detected when current flows in an unexpected path, triggering disconnection

Grounded systems require additional labeling per 690.5(C): conductors that are normally grounded may become ungrounded during a ground fault, creating a shock hazard. Required warning label at the inverter and service panel.

Equipment Grounding Conductor (EGC) Sizing — 690.43

All metallic parts of the PV system that are not part of the circuit conductors must be bonded together and connected to the EGC:

• Module frames
• Racking rails and posts
• Junction box enclosures
• Combiner box enclosures
• Conduit (metallic conduit is self-grounding when properly bonded)
• Disconnect enclosures
• Inverter chassis

EGC Size: NEC Table 250.122

The EGC must be sized based on the rating of the overcurrent device protecting the circuit:

For PV source circuits without an overcurrent device at the point of origin (e.g., a string of modules with no combiner fuse), the EGC must be at least as large as the source circuit conductors.

Module Frame Bonding

Module frames must be bonded to the EGC. The challenge: module frames have an anodized aluminum surface that provides corrosion resistance but also creates an electrical barrier. Bonding must pierce or bypass this anodized layer.

Listed Bonding Methods

The bonding method must be listed — general hardware store components that aren’t UL-listed for solar bonding don’t qualify.

Racking System Listing and Module Bonding

Some racking manufacturers (Unirac, IronRidge, Schletter) include module-level bonding as part of their system listing. When the racking system is used as specified in its listing, module frames are considered bonded through metal-to-metal contact with the grounded rail without additional bonding hardware. Verify this with the specific racking manufacturer’s installation instructions.

Grounding Electrode Requirements (690.47)

The PV system must connect to the premises grounding electrode system — the same rod(s), plates, or water pipe that ground the building’s electrical service.

Connection Point

The PV system EGC connects to the grounding electrode system at:

• The main service panel grounding electrode conductor
• A dedicated grounding electrode connection point listed for PV use
• The grounding electrode directly (a second listed grounding electrode can be added if required)

Do not create a separate isolated grounding system for the PV array — the array grounding electrode must be bonded to the building’s grounding electrode system.

DC Grounding Electrode (NEC 2020)

NEC 690.47(B) requires a grounding electrode for DC systems where the voltage to ground exceeds 250V for grounded systems. For most modern ungrounded (transformerless) systems, this provision doesn’t apply because neither PV conductor is intentionally grounded.

For grounded commercial systems with negative-ground designs at 500V or higher, a DC grounding electrode is typically required. Consult the specific NEC edition adopted and the AHJ’s interpretation.

Common 690.41/Grounding Mistakes

Frequently Asked Questions

What does NEC 690.41 require for solar grounding?

Ground fault protection for all PV systems. Modern transformerless inverters satisfy this through built-in isolation monitoring — they detect ground faults and shut down automatically. Older grounded systems use a dedicated Ground Fault Protection Device (GFPD) in the grounded conductor.

How do I bond module frames under NEC 690.43?

Use listed bonding hardware: grounding clips, Weeb washers, or racking systems with manufacturer-listed module bonding. The bonding method must pierce the anodized aluminum surface of the module frame. Unlisted hardware from a hardware store does not qualify.

What size EGC do I need for a solar PV system?

Size the EGC per NEC Table 250.122 based on the overcurrent device protecting the circuit. A 15A fuse requires a 14 AWG copper EGC minimum; a 60A fuse requires a 10 AWG copper EGC minimum.