Hi, new here so hope this is going to the right thread. The alarm panel will not sound if the system is "Unset" and the Aux supply to the PIR's is removed. It is usual however, for the "Tamper" loop to be a 24hour and it will usually initiate an internal alarm if the circuit broken. The only reason I mention this is that it would be unusual for only a supply pair of wires in a cable to be severed without generally knackering the rest of the conductors in the cable.
If the alarm has been installed by a reasonably competent person, the colour codes used should be the same for all alarm loops of the same type. If the alarm has been wired "Conventional" and not "End of Line resistor" then it usually follows that each zone is wired to a single PIR or door contact. Although, it is possible to wire several detectors in series in conventional mode, EOL mode has to have individual loops. The tamper loops are all connected for all zones in series and connected to the "Global tamper" terminals on the board. The 12V supply for the active detectors (PIRs Shock sensors, Break-glass etc) are all connected in parallel. It is usual, but not obligitory, to use the red and black wires of the 6 core cables for the 12V supply. These are usuall brought into a "Choccy block" connector and all reds go together and all blacks go together. A pair of red and black then go from the choccy block to the 12V Aux on the control panel circuit board.(The terminals on the board are a bit small and you can't get more than a few wires in them, hence the choccy block if you have a lot of active or processing detectors). If you only have 2 or 3 PIR's then the wires may be connected directly into the circuit board terminals.
You need to separate all the red wires from this terminal and test each one in turn with an Ohmeter (Resistance meter) to the black terminal. (You can leave all the black wires connected.) You are looking for a fairly high resistance, kilohms range. If any show low Ohms or zero, then that is the circuit that is at fault. Again, if the guy that fitted it was reasonably competent, the cable ends should be identified as to which zone it feeds.
You can disconnect this loop from the panel, link out the tamper and zone terminals with short pieces of wire or a cable staple to allow the zone to be temorarilly bypassed. Check the output from the "Aux 12V" and ensure the 12 VDC is present. If not, check and replace fuse if necessary). Return the panel to service whilst you trace the cable / end element and check for shorts.
Hope this info helps. ( I'm a registered Texecom installer, feel free to ask if you need any further info).
Good luck,
Nat.
