Installing Solar Electric Since 1983


Case Study: Ground Fault in PV Charging Circuit

Update: The information below and in the linked page may not be accurate. Further reflection on the problem reveals one fallacy in Theory B: The charge controller should have been able to handle steady-state fault current from the PV array since it was sized to handle the PV charge current. The cause of the fire reamins a mystery.

William Miller

The National Electric Code requires ground fault protection/detection in any photovoltaic charging circuit installed on a dwelling roof. We have seen first hand how the incorporation of ground fault detection/protection can prevent fire hazards.

The following case study illustrates this clearly. The charging source are a group of used, Cariso Plains modules that the client installed himself. During the installation, a wire was pinched but the insulation was not pierced immediately. When the insulation was eventually violated, the resultant short circuit resulted in a catastrophinc failure and fire in the charge controller.

Ground fault pictures and diagrams.

Case Study: Misleading PV Ground fault indiction

The drawing linked below indicates a scenario in which a fault which is not a ground fault does not trip the correct breaker and instead trips the incorrect breaker. The fault is not cleared in this case.

Please note that this ground fault system un-bonds the negative DC bonding system. This appears to violate NEC 690.41.

Misleading ground fault indication