Cutting and extending alarm cable problem

[Bob Eager]

MOre likely to be a NiCad or similar...

[John Rumm]

I don't know how sophisticated the "anti tamper" is - if its just a 12V hold off without any clever cable impedance change detection, then it sounds trivial to defeat.

Decide where you want the new cable to go and install it - leaving ends close to exiting cable. Strip the outer sheath of the existing cable adjacent to new cable ends, and join using a suitable terminal box[1]. Repeat at other end, now remove unwanted cable section[2]

[1] You could do a temporary bridge using a pair of IDC RJ45 sockets and a patch lead, or alternatively go for the final solution in one go. I would use something like:

one at each connection point, and bridge enough terminals with the new cable. Now strip the outer sheath from the existing cable without disturbing the wires. Punch these down into the individual terminals. At this point you should now have two parallel paths of connection, and the original wires can be cut and removed. At no time will the circuit have been interrupted.

[2] Don't just cut in one action as this could temporarily short the wires - cut each wire separately.

[Andy Dingley]

"Quite a capacitors" are now cheap and commonplace. It's also driving a high-efficiency sounder, not a bell.

As these capacitors have "building lifetime" lifes compared to lead- acid rechargeables, they're now very popular fitments to alarm bell boxes. Given the usual hassle factor of getting to the bell box, especially if its fittings are tamperproof (or simply unremovable) it can be worth changing to this sort of sounder rather than the usual pre-emptive bell box battery replacement every few years.

If your panel battery fails, the sounder goes off when the mains does. People usually fix that.

If your bell or sounder battery fails, the bell goes quiet when tampered with. This is les obvious, so it's usually ignored - even though it's a significant loss of system resistance to attack.

[Andy Dingley]

No, a _system_ is only allowed to sound for 20 minutes. A damaged or deliberately tampered with system is allowed to sound indefinitely, as there's no reasonable way the law can require it to shut up when it's damaged or comproimised from how it's supposed to work.

So the panel has a timeout after 20, but a severed bell box will keep on tweeting while the power lasts.

[Vet Tech]

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John,

Neat solution.

I have a couple of these connector boxes spare that I was going to use to extend two runs of Cat5 cable so I'll give that a go, many thanks

VT

[Man at B&Q]

Disabling then, which is the same thing as turning off that function that makes it sound the alarm.

MBQ

[Toby]

All the bell boxes I have fitted have had an internal timer in the bell box too!

[Dave Liquorice]

Yes that would work but it assumes you know which core does what in the cable. There is no standard for this and indeed there shouldn't be... A single installation or one done by the same person/company might be consistent but that is about as far as it goes.

[John Rumm]

Don't see why you need to know the function of any of the cores as long as you ensure continuity of all the wires is maintained. So bridge each wire to itself, and then cut the originals.

The difficulty may come if the cores are all the same colour - making it harder to tell which is which (although in this circumstance you could just strip all the outer from the section to be moved, and identify the cores that way)

[Dave Plowman (News)]

I've never seen a lead acid fitted to a bell box - they are usually Ni-Cads or later types. What makes used them?

[dennis]

They are also usually 12V the same as the rest of the stuff.

Don't take the cover of the strobe though as there are a few kV inside.

[JDT2Q]

An important safety tip if you intend to remove the bell box cover while up ladders and are unsure whether it will sound due to being tampered.

You will be very close to the sounder and up ladders and, close up, it should be very loud.

Your hands will probably be full too.

You natural involuntary reaction will be to draw back.

There have, I seem to recall, been instances in the past where the shock of the high intensity sound has caused the uninformed D-I-Y alarm engineer to fall off their ladders.

Just be aware and prepared for the acoustic shock and don't fall from your ladder.

[Andy Dingley]

No idea - generic tin boxes from the cheap shop when I fitted them, also some insanely expensive stuff that a friend fitted to his factory building and a fish-named locksmith came and billed them a shedload of money for annual servicing, with new batts every few years. Newer than NiCds, older than capacitors.

[Dai]

take a look on