Why Might a Solar Installation Fail NEC Grounding Inspection?

Insufficient Grounding Connections

Incorrect or missing grounding connections are a common cause of solar installation failures during NEC grounding inspections. According to NEC 690.5, a ground fault current path must be provided from the inverter or charge controller to the service equipment ground. This path is typically achieved through a grounding wire, but it must be properly sized, connected, and secured to ensure a reliable ground fault current path. A minimum 6 AWG copper grounding wire is recommended for most solar installations, and it should be connected to a grounding electrode, such as a rod or plate, in accordance with NEC 250.52.

Incorrect Bonding Between the Inverter and Service Panel

Another common issue is incorrect or missing bonding between the inverter and the service panel. NEC 250.30 requires that the inverter be bonded to the service equipment grounding system, which typically involves connecting the inverter’s grounding terminal to the service panel’s grounding busbar. This bonding connection must be made with a minimum 6 AWG copper conductor, and it must be sized to carry the maximum short-circuit current rating of the inverter. Failure to make this connection can result in a failed NEC grounding inspection.

Grounding System Design Requirements

NEC 690.5 also requires that the grounding system design must ensure that ground fault currents can be safely and reliably cleared. This involves designing the grounding system to have a low enough impedance to allow the ground fault current to be cleared within a reasonable time frame. A common rule of thumb is to design the grounding system with an impedance of 3 ohms or less. This can be achieved by using larger grounding wires, shorter grounding paths, and multiple grounding electrodes. By following these guidelines, solar installers can ensure that their installations meet the NEC grounding requirements and pass inspection.