The optimal grounding points for a PV combiner box include the combiner box enclosure grounding lug, bonding busbar, array frame grounding system, and the system grounding point at the inverter or main service.

Key Grounding Points

1. Combiner Box Enclosure Grounding Lug Connect the equipment grounding conductor (EGC) directly to the combiner box's listed grounding lug. This ensures that the metallic enclosure is bonded and provides a low-impedance path for fault currents, protecting both personnel and equipment .
2. Bonding Busbar (if present) If the combiner box includes a bonding busbar, the EGC should be connected here to establish an equipotential plane. This busbar serves as a central point for bonding all metallic components within the combiner box .
3. Array Frame Grounding System The PV module frames and racking rails should be bonded to the combiner box grounding system. This connection ensures that any fault current from the array is safely directed to ground, reducing the risk of electric shock or equipment damage .
4. System Grounding Point at Inverter or Main Service The combiner box EGC should ultimately connect to the system grounding point at the inverter or main service panel. This connection integrates the combiner box into the overall grounding electrode system of the premises, maintaining NEC compliance and system safety .
5. Grounding Electrode Conductor (GEC) to Earth For large PV systems, a supplementary grounding electrode system may be required. The GEC should connect from the combiner box to ground rods or other electrodes that meet NEC 250.50 requirements. Ground rods should be driven at least 8 feet into the earth and spaced at least twice their length apart when multiple rods are used .

Best Practices

• Use Listed Connectors: Always use UL-listed compression connectors or exothermic welds for all grounding connections; do not rely on mounting screws alone .
• Avoid Ground Loops: Connect all grounding points to a single common busbar or terminal to prevent multiple grounding loops, which can cause unwanted current flow and interfere with protective devices .
• Inspect and Test: Verify continuity from the combiner box to the array frame and system ground using a low-resistance tester. Ensure all connections are torqued to manufacturer specifications .
• Material Compatibility: Avoid mixing metals like aluminum and copper without proper antioxidant gel to prevent accelerated corrosion . By following these grounding points and practices, the PV combiner box will be safely integrated into the system, minimizing the risk of faults, voltage spikes, and equipment failure while ensuring compliance with NEC standards.