To isolate a ground fault (defined as 10 kΩ or less to ground), you must systematically narrow down the location by selectively disconnecting portions of the data loop. If the panel displays a specific device address with the fault, the issue is likely on the positive leg of that device's input circuit (Page 212) [1].
Open both conductors of the suspect loop at a point that disconnects approximately 50% of the devices (Page 212) [1].
Wait 30 to 40 seconds for the ground fault detection circuitry to respond (Page 214) [1].
Check the GND Fault LED; if it turns off, the fault is in the disconnected portion. If it remains on, the fault is in the first 50% of the loop (Page 214) [1].
If the LED went off, move your opening point electrically farther from the loop controller. If it stayed on, move the opening point electrically closer to the controller (Page 214) [1].
Repeat this process, increasing or decreasing the number of devices on the leg, until the specific wire segment or device is isolated (Page 214) [1].
For Class A loops, disconnect the return (Loop A) terminals and jumper them to the Loop B terminals to troubleshoot as a Class B circuit (Page 210) [1].
