Don,
On a two wire zone the devices, pull stations, heat heads or smoke detectors short out the wires and call in an alarm but if a wire breakes off none of the devices downstream from the break will work.The solution is that the system is designed to supervise or monitor the wires and if there is a break in the wire it sounds a trouble. The way it works is the end of the line resistor connects the two wires at the very end allowing a lowered voltage to constantly flow through the loop. This voltage is not enough to triger an alarm but it is detected by the system and asures that the wires are OK. To triger an alarm the device will short the two wires togeather and the loop passes full voltage back thus an alarm. Hope this makes sense.
Dave T.
