Fire alarms 2 core and 4core?

[Kev2632]

Can anybody explain exactly the difference between using 2core/4core to wire a fire alarm system, does the cables always go back to the controller? how is it connected when 4core cable is used?, is some of the cores joined through at the detectors/ call points?

 

[sparky3366]

got it in one...

 

[Kev2632]

got it in one...

what do you mean?

 

[sparky3366]

I do it for tidyness and ease of install, and yes cores are joined through in the call points/detectors...

 

[Kev2632]

I do it for tidyness and ease of install, and yes cores are joined through in the call points/detectors...

i suppose it saves you on time wiring two separate runs of cable yea? and does it always get wired back to the controller yea?

 

[sparky3366]

depends on the system...usually from the panel to the 1st device...then out to the next. eol devices/resistors fitted on the last sounder & call point/detector as required. Mind its a while since I have fitted any so technology might've changed...

 

[Kev2632]

depends on the system...usually from the panel to the 1st device...then out to the next. eol devices/resistors fitted on the last sounder & call point/detector as required. Mind its a while since I have fitted any so technology might've changed...

Ahh right i see, but on some systems it requires it to go back to the panel yea?

 

[sparky3366]

none that I have fitted...just like a radial circuit...

 

[Kev2632]

none that I have fitted...just like a radial circuit...

emm i thought some circuits had to go back to the control panel ... ?

 

[dubsy001]

Ive done a few fire alarm jobs now, you can have radial circuits for instance sounder circuits, there must be more than one sounder circuit incase one fails. The fire alrm circuits that return to the fire alarm panel are generally addressable systems. As for wiring in 4 core i dont think its good practice to use this as if a cable is broken, damaged or cut you will lose the remaining fire alarm circuit. When ive installed fire alarm ive always used 2 core. The last time i looked at the fire alarm regs (5839) i believe dont remember there being many definitive instructions, "it was more we recommend"
Im not to clued up on these regs so if im not quite correct i do apologise.

 

[alarm man]

in simple terms its easier to use 4-core when extending a loop more so if its a long or tricky run,it saves running 2 cables,1 pair will extend the loop from the device your connecting from and the other pair will come back and re join the loop,

 

[a1guvner]

in simple terms its easier to use 4-core when extending a loop more so if its a long or tricky run,it saves running 2 cables,1 pair will extend the loop from the device your connecting from and the other pair will come back and re join the loop,

Definately and look like a neat job that you can turn around quicker

 

[The Finch]

One thing to point out though bs5839 doesn't like you to use 4 core and prefers the use of 2 2 cores it's all to do with that they call the critical signal path and so on, up dig out my papers and find the correct reasons, basically they say stand a better chance if 1 2 core is damaged by whatever means then still got some cover on the other whereas if 4 core theres the potential to loose more

But as mentioned earlier it's sometimes neater and easier for jobs especially additions to existing systems

As for circuits going back to the panel as a ring or staying radial depends on the system, typically an addressable system will be wired as a ring or loop in fire speak back to panel, conventional standard systems go from the panel pick up devices then at the last point have an end of line which varies from a resistor or diode to active units with capacitors and little mini circuit boards then your sounders or bells again wired as seperate radial circuits