Alarms: PIR's and 8 core cable

Feb 22, 2008 2 Replies
D

If two PIR's are connected on the same 8 core cable, how are these wired up? Given there are normally 6 cores to each PIR, how are two PIR's wired with one 8 core cable?



Basically I think I have managed to put a screw through the return wires to the panel. The PIR's are still getting power and the tamper circuit has not been tripped. I spoke to the guy who commissioned the alarm (the builder installed all the cables, he just connected the panel) and he said I could take out the tamper circuit and swap the return wires with the tamper at both ends. This will cure the problem, although I will no longer have the tamper protection.



If 2 PIR's are on the one cable, are the tamper wires shared? If so, I don't think I can do as he suggests??


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A

It depends heavily on the type of panel, and the type of install (sometimes internal detectors don't even get tamper protection wired to them).

A common configuration is a single tamper loop in series through all the detectors, so there will only be one pair in the cable for it, regardless of the number of sensors/zones the cable splits off to.

Sometimes there's no separate tamper circuit -- it's done with single or dual end-of-line resistors on the zone circuits, so the zone goes different resistances for OK, tripped, and tamper.

Most likely, you have the standard 6 cores you would get for one PIR, and an additional pair for just the detector circuit on the second PIR, assuming they are on separate zones (or panel inputs).

However, given the cable wasn't installed by the alarm installer, the number of cores may not match actual usage by the alarm installer.

Can you find where you put the screw through and repair it?

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D

Hi, thanks for the reply.

I put in about a hundred screws in the upstairs landing due to loose / squeaking floor boards

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