On September 16, 2018 at 11:09, Brad Humphrey said...
If you use a EOL resistor 2x the normal value, then 2 circuits can be put on 1 zone in parallel and it works fine. i.e = 1KΩ is the EOL normally used, so put 2kΩ resistors at each detector.
That would get him down to only needing 3 zones for his 5 fire sensors. The increase in resistance would be enough to trip if 1 line went open.
Beyond that, you can use a zone expander if you really don't have enough zones to even get it down to that.
Well first of all I was responding to him putting all the detectors on one zone, there is no EOL scenario to cover that.
Secondly the doubling of resistor value may or may not work as you are effectively halving the change seen by the panel, in your example one leg going open circuit will not then show infinite resistance, but 2K instead of 1K. Depending on the panels sensitivity to resistance (voltage) change on the zone this may not be enough to trigger a fault condition. If it doesn’t register this fault then you have a circuit that will not trigger the panel when the detector is triggered as it has an open circuit leg, but the panel is still seeing an EOL on the other leg that is sufficient for it to think it’s all good. On a life safety system I would not be prepared to take that risk....
