To troubleshoot a ground fault on the NFS-320, first identify the fault location using the onboard diagnostic LEDs and then isolate the field wiring to locate the earth connection.
Check Diagnostic LEDs: Inspect the main circuit board for active indicators. LED3 illuminates for a general board ground fault, while LED10 indicates a ground fault specifically on the SLC loop (Page 5) [1].
Verify Physical Grounding: Ensure all mounting holes are secured with a screw or standoff. This is critical to maintain the continuity of Earth Ground (Page 5) [1].
Check Hardware Switches: Verify the position of SW1, which enables or disables ground fault detection, and JP1, the ground fault jumper for SLC #1 (Page 5) [1].
Identify Fault Type: Review the panel display. "GROUND FAULT" indicates a fault within the panel or general wiring, while "GROUND FAULT LOOP x" pinpoints the issue to a specific Signaling Line Circuit (Page 69) [1].
Isolate Wiring: Disconnect field wiring from the terminal blocks (such as TB13 for SLC or TB10 for DC power) one at a time until the fault clears to identify the grounded circuit (Page 5) [1].
