Alarm Help

[slackworth]

Hi All,

I have a wired alarm system in the house which was working absolutely fine until recently but one of the PIRs has appeared to die and as a result the alarm won't arm unless I omit the area.

Two PIRs are wired to Zone 3 in the control panel and oddly The one at the back of the room works but the other at the front of the room is dead. I've purchased a new PIR to try assuming it was that and its still dead (however the 2nd PIR still works). I've tried measuring the power with a multimeter and there's absolutely nothing there which is obviously why it's not working.

At the control box there's only one set of 6 cores wired for both sensors so would assume they are wired in series however out of the working PIR I was expecting two sets of cables - one to the alarm box and one to the other sensor but that isn't the case - both PIRs have 1 wire coming out of them. I have tried wiring the "dead" sensor directly into the control panel with a short bit of wiring to test and it bursts into life no issues.

What I don't understand is quite how the sensors are wired in series if there's only one set of wires to each PIR and secondly is there anyway of fixing the wiring given its all buried underneath the upstairs flooring and no idea whereabouts it runs? If there is no way of fixing it without lifting all the floors, is there anyway somehow of knocking the "dead" sensor out so that the single sensor could work on its own?

Many thanks

 

[EightyTwo]

The power for both PIRs will be in parallel and the alarm pairs (and tampers) in series so, if there's only one cable in each, the cables must go back to a common point. This could be a junction box or within the panel itself. JBs could be long and thin like HD door contacts (about 15mm x 15mm x 70mm), flat squares (about 50x50x10mm) or larger ones about the size of a margarine tub.

Search out the common point and see if there is power. If you have some cable damage, use spare cores (or the tamper pair). If you can't track down the fault, link the alarm pair in the duff PIR (just put both wires into the same terminal). These could be labelled as C(ommon) and N(ormally) C(losed) in the PIR.

 

[slackworth]

Hi, thanks for replying so quickly!!

I'm definitely not aware of any surface mounted junction boxes which unfortunately means it's likely to be buried in the lounge ceiling somewhere between the two PIRs roughly in the middle which would make sense for wiring it into the alarm box which is on the other side of the wall.

I'll try wiring in the two wires together to see if that makes it arm. I did twist those and the two tamper wires together but it still wouldn't let me arm without omitting the zone but perhaps it needs to be on the terminal block instead. Should it work even if there is no power or is this needed for the resistance side of things so the control panel doesn't detect an open circuit?

 

[EightyTwo]

If it's wired as 4-wire (alarm pair and tamper pair), you just need to link the alarm pair together (the PIR's tamper switch will link the tamper pair). If you've got EOL resistors, you'll probably need to keep them in circuit (in this case, the two PIRs' alarm pairs are probably wired in parallel whilst the tampers will be in series).