Grounding of Photovoltaic Inverter and Distribution Box

Proper grounding of PV inverters and distribution boxes ensures safety, protects equipment, and stabilizes system voltages.

Key Concepts

System Grounding vs Equipment GroundingSystem grounding connects the electrical system to earth, providing a reference voltage and helping clear faults. Equipment grounding bonds all non-current-carrying metallic parts (frames, racks, enclosures) to create a low-impedance path for fault currents, ensuring protective devices trip reliably. Bonding ties all metallic components together to prevent dangerous voltage differences, while isolation may be used in transformerless inverters with ground-fault detection.

PV Inverter Grounding

Each inverter must be individually connected to the main grounding busbar; never connect inverter grounding cables in series. The chassis of the inverter must be grounded through the equipment grounding conductor, and the AC side connects to the main service panel with a single neutral-to-ground bond to avoid parallel paths and GFCI issues. Transformerless inverters often use ungrounded or floating DC arrays with electronic ground-fault detection, while solidly grounded PV source circuits remain a permitted configuration.

Grounding conductors should have sufficient ampacity, typically 25% greater than the system's maximum fault current. Copper-clad rods are preferred in high-moisture environments for durability.

Distribution Box Grounding

The distribution box must be bonded to the equipment grounding conductor and, if required, connected to the premises grounding electrode system. Auxiliary grounding electrodes at the array are optional but must be bonded to the main grounding system to prevent potential differences. Proper sizing of grounding electrode conductors follows NEC 250 rules, including 250.

66 for conductor sizing.

Practical Considerations

Line resistance of grounding conductors should be minimized (recommended