Alarm installation - cable type query

[Guest rjenkins]

I've only recently joined this group & I've been browsing through the existing posts, generally looking for hints & ideas in preparation for replacing an old & nasty alarm installation at a house I just bought.

One of the other threads in this topic mentions cable types & it has me puzzled. I've started a new post rather than hijack the other thread.

Just out of curiosity, why isnt alarm cable screened or twisted pair.

Because EVERY core in the cable has to be SAME length. In TP cables pairs are twisted in specific manner and therefore are not suitable for alarm applications.

It can be manufactured as screened. I can provide you with this kind of cable if no-one volunteers to.

In UK you HAVE TO USE UK TYPE ALARM cable which politicians have decided to be BEST for the alarm systems.

(remainder trimmed out).

I don't follow the reasoning on this.

In any good twisted pair data cable, the two cores in each pair will be very closely matched in length. There will be some difference in length between different pairs due to the different twist pitch of each pair, but it will only be a few percent.

The normal cable used for alarm systems is fairly cheap & nasty stuff, it's nothing like the quality of a generic industrial 7 x 0.2 multicore. (But it's also nothing like the price..)

Alarm systems are mostly DC, I would guess that the highest frequency involved will be the serial comms between the keypads and the main alarm unit, and this is probably 1200 or 9600 baud at most.

Gear like this that is designed to work on unscreened and untwisted cable is surely not going to be affected by even large differences in the lengths of cable cores.

Are there actually any specific fixed requirements for the type of cable used in alarm systems, or is there just a minimum specification?

I can understand that CW1308 & CAT5 installation cables etc. are not suitable as these are single strand and far more likely to fail under vibration or flexing, but beyond being reasonable quality stranded core, what is required?

I was specifically planning to use screened twisted pair for linking the keypads to the main unit on my new installation, so I am very curious about this!

[ian.cant]

I am not well enough edumacated to give you the specific reasons why one cable v another type should be used.

However i am edumacated enough to know that BS4737 (the british standard for intruder alarm installation) states that Alarm cable is to be used, its doesnt say dont use cheap and chatty cable, just alarm cable, as supplied by alarm system wholesalers nationwide.

I am sure there many good reasons why that is, you may use whatever you like but us proffessional installers have to install to the relative British Standards.

As for using shielded twisted pair, some systems do have the the data lines run in this type of cable, as specified by the manufactures. General alarm cct's should be run in alarm cable, i guess thats why they call it alarm cable.

[Guest]

it is UK reg's that say for example that cores _have to be same length_ . I do _not_ see any electrical benefit in that thou.

Also it has to be tinned multistrand cable. This i do not disagree with. At all. I have personally used (because here in coldshire it is completely OK) CAT3 (CAT5 is too tough and weak) telephonecable that is single strand. In permanent installations it is ok but if there is vibrating / bending then naturally the choice will be multistranded. You also have to be extremely careful when stripping the cores. There are thou special tools for that purpose. BUT in UK it is AGAINST REG's.

Reg's in UK also say what kind of material the cover of the cable has to be. How resistant for heat etc.

That's why i underlined in that previous post that in UK you USE UK type alarm cable. Nothing else. Thou some people here use belden cable ( i have heard so ) which is TP as i have understod it.

[Guest]

Im curious - you know alarm cable exists - yet you think you can invent another system for doing things, why change anything when the proper cable already exists???

This is a reason why I dont like people doing DIY systems, because when they start false alarming it gives the industry a bad name, and it just makes people ignore them even more.

[Guest rjenkins]

I'm an electronics designer & programmer (of industrial embedded controllers, radio data links, machine tool & factory automation controls etc.) with 25+ years experience.

I have no formal knowledge of the specific regs & requirements of alarm systems beyond basic common sense & good practices, hence the questions!

I'm also a Radio Amateur datacomms enthusiast, so this place is a rather hostile environment for anything that's not proof against fairly high levels of pulsed RF..

From what I have been able glean via Google about BS4737 Section 3.3 (which appears to be the bit covering cables?) the specs for the cable appear to be limit values - such as minimum insulation thicknesses & maximum resistance - not absolute fixed values. (At least those are the most frequent 'brag points' in manufacturers spec sheets).

If this is the case, any cable that meets or exceeds these criteria is automatically compliant with the standards.

If anyone has access to BS4737 or it's successor, I'd appreciate an outline of what it states in the cable specs..

Just stating it says 'use alarm cable' is something of a circular argument, as all the manufacturers data I've found states that their (alarm) cable 'Meets the requirements of BS4737 Section 3.3' or something to that effect.

I don't want any possibility of faults or false alarms due to RF or other electrical interference, plus I have lots of part reels of various screened 7x0.2 & 16x0.2 multicores, which have the same or better specs that normal alarm cables.

[Stealth]

Go buy some 8 core alarm cable!

[Guest]

LOOK - Does it matter!

The MANUFACTURERS of their OWN panels specify a maximum of SCREENED alarm cable in hostile environments, they dont say run CAT5 or telephone cable with tin foil wrapped around it grounded to a 3 foot spike buried in the ground do they!!

Alarm cable - usually 8-core, and where necessary screened, is perfectly fine and as stated in hostile environments 8 core screened alarm cable is perfect.

Where is everyone going on this??

Im off outside to see if I can make my cars wiring out of tin foil - JUST FOR FUN.

[Guest]

Basically its as I thought, YOU have part reals of cable, so YOU want to re-write the book on how alarms are installed and to what standard.

Im sorry for being harsh I really am!

But you are just trying to justify your own shortfallings and you want to save money so you dont have to buy the proper cable.

I appologise again for my frankness - and mods please delete or repremand me - but what I speak is the TRUTH.

[ian.cant]

I'm an electronics designer & programmer (of industrial embedded controllers, radio data links, machine tool & factory automation controls etc.) with 25+ years experience.

With your qualification your clearly better edumacated than me!

Ive already stated what the recommended cable is to use and your questioning that so clearly your going to use whatever cable you have "lying around".

I understand why you would consider using a shielded cable in the circumstance you have described, no doubt you will and it will work electrically of course.

Your plan falls flat on its face though as none of the sensors or control panels will be shielded, as far as i am aware no one makes equipment for the security alarms market that is protected from strong radio signals.

My advice to you would be to use the manufactures cable recommendations and if your not happy with that take it up with them.

[Guest]

I think we want to be carefull about jumping down this guys throat like I did, so again I appologise for that, but my opinion has not changed, the way I expressed myself could have been better I admit.