To isolate a ground fault on an EST4 Signature loop, use a systematic split-and-search method to narrow the location to a specific wire segment or device. The system reports a ground fault when resistance to ground is approximately 10 k̦ or less (Page 164) [1].
Check the Ground event queue; if a device address is listed, the fault is on the positive leg of that device's input circuit (Page 164) [1].
If no address is shown, open both conductors of the loop at a point that disconnects approximately 50% of the devices (Page 165) [1].
Wait 30 to 40 seconds for the ground fault detection circuitry to respond after the fault is removed (Page 165) [1].
If the Ground event clears, the fault is on the disconnected portion; if it remains, the fault is in the first 50% of the loop (Page 165) [1].
Reconnect the loop and repeat the process at a new point-moving electrically farther if the fault cleared or closer if it remained-until the fault is isolated (Page 165) [1].
Verify the fault is cleared by measuring voltage between earth ground and logic negative, which should be 12.3 to 16.8 VDC during the 2-second test performed every 18 seconds (Page 165) [1].
