Identifying the cause of a Fire Call.
In NZS4512:2003 Panels, the MCP’s and Heat Detectors are indicating, and when in Fire will bring the circuit voltage down to around 11-12 volts, depending on the model of Fire Panel. In our addressable Panels, it will depend on which Conventional Interface is used. Smoke Detectors will bring the circuit voltage down to about 9-10 volts.
In NZS4512:1997 circuits, MCP’s and Heat Detectors will open circuit on operation, and so the circuit voltage will rise slightly while the circuit is in fire. If possible, use another circuit to identify the ‘normal’ voltage. Smoke Detectors will bring the voltage down to about 9-10 volts, as in the 2003 circuits.
If the voltage on the circuit is between aprox 9 and 12 volts, then the ‘Fire’ condition is still there, and you should be able to see an indication on a Detector. If it is a 1997 circuit, and the voltage is higher than normal, then you will be looking for a Heat Detector or MCP on, or ‘open circuit’.
In all cases, if the voltage on the circuit is normal, the cause of the Fire condition is no longer present. You may need to check the whole circuit for a loose or corroded connection.
FireFinder: Another cause of frustration is not being aware of how to find faults on the FireFinder addressable loop. This can be simplified for testing purposes by removing one end of the loop (usually the ‘B’ or return/In side), which converts it from a loop, to a single ended cable. You can link the Out and In (A and B) terminals together at the Loop Driver Board to prevent the loop Open Circuit fault if preferred. Loop breaks will then be more easily locatable by looking at what devices are missing, and it will also be easier to locate earth faults and Data corruption by isolating parts of the cable.
It is recommended to remove the 20 way ribbon cable from the loop driver board before disconnecting and reconnecting the loop, as this will perform a ‘soft start’ when the ribbon is reconnected. It will also cause the Panel to perform a loop test when reconnected, which will eliminate the necessity to perform a manual loop test.
Finally a reminder to sensible Tech’s: Always remember to remove all power to a Panel before adding or removing PCB’s and interconnecting cables, as most PCB’s are not ‘Hot Swappable”. Re-power by Mains, then battery whenever possible, to eliminate power surges. Also, be very careful while working on a live Panel! Many a PCB has been damaged by bared cables or screwdrivers going where they shouldn’t on a live PCB.
-Colin Oldale- Technical Support NZ