5.2.1.3 All Detectors in fault
If all the detectors connected to the Control Panel are shown with a Backup Alarm Fault the
Control Panel Interface Board should be replaced.
5.2.2 Communications Fault
Under normal operating conditions the Control Panel polls each of the detectors one at a time with the
detector responding each time. If when the Control Panel polls a detector it fails to get a response or
the response is corrupted the Control Panel will indicate a communications fault, see section 5.1.1.
Figure 137 Communications Fault
Alternatively, an inspection of the engine event log, see section 3.6, will list the event:
Comms Fault Eng X det Y
5.2.2.1 Cable Screening
A major cause of communications faults is incorrect screening of the cables.
1. Ensure that screened cables have been used for both the communications and power supply
connections between the Control Panel and each Junction Box. The outer braid surrounding
armoured cable must NOT be used as the cable screen.
2. At the Control Panel ensure that the communications and power supply cable screens are connected
directly to the earth via EMC metal glands.
3. At the Junction Box ensure that the communications and power supply cables pass through the
plastic glands and the screens are terminated in the SCN terminals in the Junction Box.
Figure 138 Control Panel to Junction Box Terminations
4. Disconnect the screens from the SCN terminals in the Junction Box. Using a multi-meter measure
the resistance between the SCN terminals and the Junction Box earth stud. The resistance
measured should be >10MΩ.
If the resistance is less than 10MΩ the Junction Box PCB should be replaced.
5. Reconnect the cable screens in the SCN terminals.
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