On an MXL system, loop-related troubles typically refer to either network communication failures or faults on a Notification Appliance Circuit (NAC). Network Loop A Failure or Network Loop B Failure indicates that the Style 7 primary or secondary RS485 MNET network loop has failed (Page 148) [1].
If the message is Signal Circuit Loop Open, the NAC has a broken wire or a missing EOL device; Signal Ckt Loop Shorted indicates a short circuit, an incorrect EOL value, or notification appliances that are not polarized or are connected backwards (Page 149) [1].
To clear the message from the display:
Acknowledge the condition by pressing the [Tab] key or entering the AT [Return] command (Page 19) [1].
Physically resolve the underlying wiring fault, such as repairing an open circuit or correcting the polarity of appliances (Page 149) [1].
Note that unlike the XL3, the MXL does not have a loop disarm feature (Page 20) [1].
