Grounding and Bonding for PV Systems: A Comprehensive Guide to NEC 690 Part V

Properly grounding solar PV systems is one of the most critical aspects of a safe and reliable installation, governed by Part V of NEC Article 690. This process involves two distinct but related concepts: system grounding, which connects current-carrying conductors to the earth for voltage stabilization, and equipment grounding, which bonds all metallic components to prevent shock hazards. Key components in this process include the Equipment Grounding Conductor (EGC) for fault current paths and, in some cases, a Grounding Electrode Conductor (GEC) to connect to a grounding rod. Modern installations frequently use a functionally grounded inverter with an ungrounded PV array, a shift from older solidly grounded system designs. Adhering to the nec code book ensures that listed grounding and bonding devices are used to maintain electrical continuity, protecting both people and the expensive solar panel generator equipment.

The Foundation: Grounding vs. Bonding in Solar Installations

For any master electrician or journeyman electrician, understanding the distinction between grounding and bonding is fundamental. While often used interchangeably, they serve different purposes under the National Electrical Code. Grounding is the act of connecting an electrical system to the earth, primarily to limit voltage spikes from lightning or utility surges. Bonding, on the other hand, is the process of connecting all non-current-carrying metallic parts of an equipment or enclosure together to create a continuous low-impedance path. If you need a refresher, our articles offer a deep dive into grounding vs. bonding as defined by NEC 250 and the specifics within NEC Article 250.

In a solar PV system, the goal of this combined effort is twofold: personnel safety and equipment protection. Proper bonding ensures that if a fault occurs and a metal frame becomes energized, the current has an immediate path back to the source, tripping the overcurrent device and preventing a dangerous shock hazard. Grounding helps stabilize the system’s voltage relative to the earth. While Article 250 provides the general rules, NEC Article 690, Part V, modifies and adds specific requirements for the unique characteristics of a solar panel generator.

Decoding NEC 690 Part V: System Grounding Approaches

NEC 690.41 outlines the permitted system grounding configurations, giving installers different approaches based on the equipment used. The choice between these systems impacts everything from safety device requirements to overall system efficiency.

Solidly Grounded Systems

A solidly grounded system is a traditional design where one of the DC conductors (typically the negative) is intentionally connected directly to ground. This approach requires the installation of a ground fault protection device (GFPD), as detailed in NEC 690.41(B). This device is designed to detect and interrupt low-level fault currents that may not be high enough to trip a standard overcurrent device but could still pose a fire risk. The GFPD monitors for current imbalances and will disconnect the faulted circuits to ensure safety.

Ungrounded PV Arrays and the Functionally Grounded Inverter

The modern trend in residential and commercial solar is the use of an ungrounded PV array paired with a non-isolated, transformerless inverter. In this setup, neither the positive nor negative DC conductors are bonded to ground. Instead, the system relies on a functionally grounded inverter. This type of inverter doesn’t have a direct, solid connection to ground. Instead, it uses advanced electronics to monitor the system and establish a ground reference for operational and safety purposes, such as fault detection. If a ground fault occurs, the inverter detects it and ceases operation. This design, often referred to as a “non-isolated system,” has become popular due to higher efficiencies and lower costs.

Equipment Grounding: Ensuring Electrical Continuity

According to NEC 690.43, all exposed non-current-carrying metal parts of PV modules, racking, and enclosures must be bonded together and connected to an equipment grounding conductor (EGC). This is non-negotiable and is a frequent point of failure in inspections. Deficiencies in system and equipment grounding are a common issue that can impact system performance and pose a risk of electric shock.

The Critical Role of the Equipment Grounding Conductor (EGC)

The Equipment Grounding Conductor (EGC) is the backbone of equipment safety. Its job is to provide a reliable, low-impedance path for fault current to travel from the site of the fault back to the power source, allowing the overcurrent protection device to operate quickly. The EGC must be sized according to NEC 250.122, based on the rating of the overcurrent device protecting that circuit. An undersized EGC is a serious hazard, as it can fail during a fault condition.

Array Mounting System Bonding and Listed Devices

Ensuring PV module grounding and proper array mounting system bonding is crucial for maintaining electrical continuity across the entire array. Early installation methods required running a copper wire and individually attaching it to every single module frame—a time-consuming and expensive process. Today, the industry relies on listed grounding and bonding devices that are certified under UL 2703. These components, such as specialized clips, washers, and bonding jumpers, are integrated directly into the racking system. As rails and modules are assembled, these devices pierce the anodized coating of the aluminum frames, creating a secure and reliable bond from module to module and down to the main equipment grounding conductor. This dramatically simplifies installation while ensuring a code-compliant bond. Following the manufacturer’s instructions for these devices is essential for a safe system.

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The Grounding Electrode System (GES)

The Grounding Electrode System (GES) is what connects the entire electrical system to the earth. This is typically accomplished via one or more grounding electrodes, such as a driven grounding rod or a concrete-encased electrode.

Sizing the Grounding Electrode Conductor (GEC)

When a DC grounding system is required, a Grounding Electrode Conductor (GEC) is used to connect the grounded conductor of the solar equipment to the grounding electrode. The sizing for this conductor is determined by NEC 250.66. For detailed guidance on this, our articles provide a complete walkthrough on sizing the GEC based on 2023 updates and how to use NEC Table 250.66 effectively.

Do PV Systems Need a Separate Grounding Rod?

A common point of confusion is whether a separate grounding rod is required at the array. According to NEC 690.47, a separate DC grounding electrode is generally not required for functionally grounded PV systems connected to a building that already has a code-compliant GES. The array’s equipment grounding is achieved via the EGC run with the output circuit back to the main service panel, which is already connected to the premises grounding electrode system. While installing an additional, or auxiliary, electrode at the array is permitted by NEC 690.47(B), it is not mandatory and must be bonded to the main GES to prevent voltage potential differences between different parts of the system. For more information on installation specifics, see our guide on how to install a ground rod per the NEC.

Step-by-Step: Verifying an Equipment Grounding Path

1. Identify Components: Systematically identify all metallic components that must be bonded. This includes PV module frames, racking rails, the DC combiner box, inverter chassis, and any metal enclosures for components like a DC-to-DC converter.
2. Confirm Listed Devices: Verify that all hardware used for bonding—such as clamps, lugs, and splices—are listed grounding and bonding devices certified to UL 2703 and are being used according to the manufacturer’s installation manual.
3. Check Mechanical Connections: Physically inspect all bonding connections. Ensure that mounting clamps, bonding jumpers, and lugs are torqued to the manufacturer’s specifications. Loose connections are a primary cause of failure.
4. Test for Electrical Continuity: Use a multimeter or digital low-resistance ohmmeter (DLRO) set to a low-ohms scale. Test the path from the metallic frame of the furthest module in the array back to the ground bus bar in the inverter or combiner box. While a reading of less than 0.1 ohms is a common industry benchmark, always consult manufacturer specifications or industry standards for the acceptable resistance threshold to confirm a solid bond.
5. Inspect the EGC: Visually inspect the main Equipment Grounding Conductor (EGC) from the array to the point of connection with the premises grounding system. Confirm it is correctly sized per NEC 250.122 and that its terminations are secure.
6. Document for Inspection: Take photos and make notes of the grounding methods used. This documentation is invaluable for demonstrating code compliance to the AHJ (Authority Having Jurisdiction).

Key Considerations and Common Pitfalls

Proper electrician training must emphasize avoiding common installation errors. According to data from the Institute for Building Technology and Safety (IBTS), wire management failures occur on 38% of PV projects, and these failures can lead to earth faults that reduce productivity and pose serious safety risks. Here are some key points to watch:

• Improperly Secured Conductors: Wires rubbing against sharp edges of the racking or module frames due to wind or thermal expansion can lead to insulation failure and ground faults.
• Ignoring Manufacturer Instructions: Using listed components incorrectly, such as over-torquing a bonding lug or using it with an incompatible module frame, voids its listing and creates a weak point.
• Corrosion: Using incompatible metals (e.g., a copper lug directly on an aluminum frame) can cause galvanic corrosion, which degrades the electrical connection over time. Always use tin-plated lugs and stainless steel hardware designed for this purpose.
• Incorrect EGC Sizing: Failing to size the EGC based on the overcurrent protection device rating is a critical safety mistake.
• Misunderstanding System Type: Confusing the requirements for a solidly grounded system with those of an ungrounded PV array can lead to incorrect or missing components, such as a GFPD where one is required.

Primary Sources

• NFPA 70, National Electrical Code (NEC), Article 690
• UL 2703, Standard for Mounting Systems, Mounting Devices, Clamping/Retention Devices, and Ground Lugs for Use with Flat-Plate Photovoltaic Modules and Panels

Frequently Asked Questions (FAQ)

What is the difference between an EGC and a GEC in grounding solar PV systems?

The Equipment Grounding Conductor (EGC) bonds all metallic, non-current-carrying parts of the system together and provides a path for fault current to return to the source. The Grounding Electrode Conductor (GEC) connects the system’s grounded conductor (in a grounded system) or the GES to the earth via a grounding electrode, like a ground rod.

What is bonding, and does it mean the same as grounding in a solar panel generator system?

No. Bonding connects metallic parts to each other to ensure they are at the same electrical potential. Grounding connects the system to the earth. Proper bonding is what allows the EGC to safely clear a fault, while grounding protects against external voltage events like lightning. You can explore this topic in-depth in our article comparing grounding and bonding.

Is a separate grounding rod always required for a PV array?

No. For most modern, grid-tied systems using a functionally grounded inverter, the array’s equipment is effectively grounded through the EGC connecting it back to the building’s main electrical service, which already has a grounding electrode system. An additional electrode at the array is permitted but not required by the NEC.

How does the 2023 NEC code book change PV grounding requirements?

The 2023 NEC continues to refine and clarify grounding rules. A key change is in NEC 690.43(C), which now explicitly states that equipment grounding conductors are permitted to be run separately from the PV system conductors *within* the PV array. However, where the PV system circuit conductors leave the array, the equipment grounding conductors must comply with 250.134, which generally requires them to be run in the same raceway, cable, or otherwise with the circuit conductors. This revision provides clearer guidance for routing the EGC in different parts of the installation.