House alarm PIR sensor issue

Discussion in 'Tech Talk' started by Cupoftea, May 28, 2021.

  1. Cupoftea

    Cupoftea New Member

    Yep, looks like a cable issue, you know that the power cores are OK, so you could take readings again, but use either the red or black to the greens and yellows in turn, this would tell you if just one core is broken or both.
    If just one then there is a possible way to bodge a working pir.
    The zone/alarm cores are basically a -ve coming out of the zone terminals and returning to the zone terminals.
    So you could, theoretically loop the -ve in the pir to one side of the alarm contact, and use a good core, yellow or green, to the other side of the alarm contact, and bring this into the relevant return terminal for that zone.
    No guarantees that this will work on your panel, I have done it in the past, depends on the panel, and it would be suck it and see as to which zone terminal it returns on, normally the right hand side one.
    Even more preferable is to run a new cable, but obviously I don't know how easy that would be to achieve.

    Right. I see. That makes sense. So, if (for eg) the yellow was fine (and green broken), keep the yellow in the PIR and at panel as it is, disconnect the green at the PIR/panel ends, and use a small piece of core to loop from the black core to the 'hole' (sorry) where the green previously was in the PIR and in the panel itself, sharing the black wire for both the -ve of the power and the alarm circuit.

    Are there any risks with this do you know?

    I'd rather not run new cable as it'd show up (would have to run it along the walls), but I suspect that's going to be needed. Btw, the power to one of affected sensors has now gone. Might be wrong but this might suggest some mouse or so activity (no recent building work done). Not sure if the fact that the wires are plastered over might cause them to decay.

    Thanks again for the tip.
  2. Rulland

    Rulland Screwfix Select

    No risks, unless of course you short +ve to -ve, then you'll blow a fuse, other than that you've nowt to lose by trying it.
    If some of the cable route is in lofts or voids I'd suspect rodent damage, meeces love alarm cable, seen loads damaged, and yours sounds like it's progressing, which again suggests damage at spaced intervals and not a straight slice through the whole cable.
  3. Cupoftea

    Cupoftea New Member

    No risks, unless of course you short +ve to -ve, then you'll blow a fuse, other than that you've nowt to lose by trying it.
    If some of the cable route is in lofts or voids I'd suspect rodent damage, meeces love alarm cable, seen loads damaged, and yours sounds like it's progressing, which again suggests damage at spaced intervals and not a straight slice through the whole cable.

    Yep, some of it does run under floorboards.

    Thanks again for the tips.
  4. Rulland

    Rulland Screwfix Select

    Not a problem, that's why we're all here :)
  5. Sparkielev

    Sparkielev Screwfix Select

    My mistake was reading it as solid lights on panel not pir
    Rulland likes this.
  6. Cupoftea

    Cupoftea New Member

    Hi Rulland,

    Just an update.

    Twisted each of the alarm wires (green/yellow) in turn together with the black earth at the PIR end and tested for continuity at the panel in each case. Got continuity with the green/black twisted together (not with the yellow). Disconnected the yellow from the PIR then, using one of the cores from some alarm cable, bridged across from the yellow connection to the earth connection in the PIR. Then bridged across from the earth to the yellow side of the circuit for the zone for that PIR at the panel. Tested for continuity at the zone in the panel and now showed continuity (hadn't before).

    Set the alarm. PIR still showing solid red at the alarm keypad! (btw, the keypad seems to make a funny chirping noise alongside it's usual beep beep beep.)

    I know you said it might not work - depending on the panel (think I've done it correctly). Perhaps that the case.

    Thanks again.
  7. Rulland

    Rulland Screwfix Select

    Hi, couple of things to try now, one, try the return core from the pir in the other zone terminal, see if that makes a difference, if not try a link in the zone terminals, we're basically shorting that zone out at the panel and telling it that there is a normally closed circuit there, albeit just a link, either way it'll give us more info.
    I can't guarantee what the outcome will be with trying to fool the panel zone by using the ,-ve looped through, as I said earlier, but if the panel still shows the zone as 'active' even when there is a hard wired link in that zone, it suggests to me that the panel is faulty.
  8. Cupoftea

    Cupoftea New Member


    "...try the return core from the pir in the other zone terminal, see if that makes a difference"

    Sorry, not 100% on this. Currently I have (in the panel) on the L-H side of the zone the green (seems to be OK) core and on the R-H side a bridge from the -ve of the panel. Should I try to swap them, or just put the green in the R-H side along with the bridge from -ve?

    Think I might have already done the 'linking' out of each of the affected zones test (see test #5 above).

    Hoping I've not been too unclear with the terminology ('panel'). Just in case it's not been clear, at the actual panel (battery, circuit board with all zones etc), where I've been doing all the testing, is in the cellar and the 'keypad' (where you enter the code to set/unset the alarm) is next to the front door. I've not touched the keypad at all, but it is here that the 'red' lights for each zone are showing (inc. the ones that are solid red for the zones in question), and the 'beep' tone (with additional chirping) is coming from, if that makes sense.
  9. Cupoftea

    Cupoftea New Member

    Dear all,

    May be tempted to look inside the (separate from the panel) keypad next to the front door.

  10. Rulland

    Rulland Screwfix Select

    You need to link the -ve at the pir to one side of the alarm connections in the pir, then the good core to the other, then at the panel zone terminals try that returning good core in one side then the other, to see if the zone goes clear.
    The keypad just takes data on this system so it shouldn't cause any issues mate.
  11. Cupoftea

    Cupoftea New Member

    Right, thanks. That makes sense (just out of interest, do the core colours normally indicate which is the returning one?)

    Sorry to ask a stupid question, but when I swap the good core to the other side of the alarm connection I obviously also swap across the -ve core to the side where the good core had just been?

  12. Rulland

    Rulland Screwfix Select

    At the pir the alarm connections are basically just a switch, it doesn't matter which side you loop the -ve to and the good core, it'll still work.
    The one that will make a difference is at the zone in the panel, it sends a -ve out and expects to see it return, the question is, which one is the return, trial and error, only two permutations, if the zone light doesn't go off in either terminal, then it's a good indication that the panel could be faulty.
    If you link directly between the zone terminals with a short bit of wire and the light stays on then the panel isn't seeing the zone go clear, best guess, new panel.
  13. Cupoftea

    Cupoftea New Member

    Thanks for the explanation.

    Have linked the affected zones out at the panel previously, as you suggest. The keypad behaved normally (zone went clear). Lit solid red again when I reconnected the PIR.

    Will try swapping the green and -ve around in the panel. Thanks again.
  14. Rulland

    Rulland Screwfix Select

    You don't need to loop a -ve at the panel, one of the terminals is already that the question is which is which.
  15. Cupoftea

    Cupoftea New Member

    Right. At the moment the green core is in the left terminal and the -ve ( bridged from the -ve side of the power) in the right. Shall I just remove the -ve altogether and put the green one in the right, then try to set the alarm with the keypad and see if the PIR has cleared?

  16. Rulland

    Rulland Screwfix Select

    Yep, just try the green in one then the other and see if you can set mate.
  17. sparky steve

    sparky steve Screwfix Select

    You proved it was a wiring issue in #6. You linked out affected zones.Then you stated panel behaved normally! Then you stated you connected the affected PIRS on a short lenth of cable, and again you stated the PIRS were working as expected! You then concluded your original wiring to the affected sensors was indeed faulty!

    Just to reiterate. You removed the wiring for the two affected PIRS at the panel. You then linked out both affected zones. You then
    tested the panel & it behaved normally.
    Then you removed the links from the affected zones, then connected short lenths of cable to the PIRS and connected the new short lenths of cable to the said zones.
    You then indicate both panel and PIRS work/function as they should.
    Therefore this indicates you have a fault on the existing cables.
    Last edited: Jul 7, 2021
  18. FlyByNight

    FlyByNight Screwfix Select

    Just to answer that point: NO there is no standard. Installation companies tend to have their own preferred scheme and even then when you get to 8 core, the one or two of colours occasionally change.

    Some always use Red & Black for 12v & 0v, others chose Brown & Blue, have also come across Yellow & Green. Just keep the same in use throughout.
  19. Cupoftea

    Cupoftea New Member

    Yep, that's what I concluded also. Rulland's helpful suggestion was to test if one or both cores of the alarm circuit were faulty. The point of this was not just to find that out for the sake of it, but, if one of the two cores was still intact it might be possible to use that intact core and the -ve of the power circuit to create an alarm circuit for that PIR (bridging across from the -ve to the zone terminal in the panel - Rulland admittedly referred to this as a bodge, but suggested it still might work, and be safe). On testing I did get continuity with one of the cores and the -ve, so, connected as above (intact core and -ve), re-checked continuity and closed the panel. But, the problem was still there, even though I now appeared to have a closed alarm circuit. That was the bit I was confused about.
  20. Cupoftea

    Cupoftea New Member

    Thanks. Tried this but didn't solve the problem (just the green in each terminal for that zone in turn, with black completely removed)

    Just to re-iterate, I tested for and got continuity at both the panel and PIR with green core and black -ve core fix, so not sure why this didn't fix the open circuit issue. Must just be that the panel won't have it.

    Have also had this green/black -ve fix in a spare zone on the panel and the solid red showed up under that zone on the keypad when I went to set it.

    Will now have a measure to see how much alarm cable I need, and hope that will fix the issue.


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