Abstract: A fault detection system comprises a photo voltaic (PV) source responsive to incident sunlight to generate output power along output conductors. Control circuitry monitors to PV source and disables output power from the source in response to detection of a fault condition. The PV source may be situated on the roof of a structure and includes an array of modules. One or more controllers monitors the output of the PV modules and a combiner is electrically connected to an output of each controller for combining DC output power from the modules into a combined PV source power output. The combiner is capable of disabling the PV source power output upon detection of a fault condition by any of the controllers, and an override switch is preferably displaced from the PV source at a remote location.