Earth cable used for twin wire system

[Guest WayneSut]

Hi i recently did a service on a two wire system fire alarm and noticed the the cable used for the zones was wired in twin and earth cable, does this have to be replaced as it also provides the supply to the multi sensor heads which incorparates the sounder also? Any advice you could send me on this subject would be much appreciated, thank you Wayne

[CWEENG]

The short answer is that,

For installations in non domestic buildings, twin and earth cables normally used in normal electrical installations is not suitable or compliant with the requirements for the installation of Fire Detection and Alarm Systems. A system installed in this way would not be compliant to BS5839-1.

With a bit more info about the site and the installation I would be able to point you in the right direction as how to proceed and what recommendations you will need to be making to your client so that he can make the decision on what to do.

[green-foam]

If its a two wire system each unit with its own integral sounder and wired in twin and earth, the probability is that it has been installed by an electrician, which then brings into question is the alarm actually suitable for its location, and what else is wrong.

I would also have to ask, if you serviced it, what is your normal job? sorry, but I can not help but wonder why you are asking such a question if you are servicing a fire alarm.

[Guest Darren]

Hi I am servicing a fire alarm in a hmo property with students in. The sounder circuit are wired in fire resistant cables but the zone circuits are in twin and earth. All detectors are suitably sited and in working order. I was always under usumption this was ok. But I have differently lately. Can I still pass this system 

[AnthonyB]

Before 2002 it was still permissible for detection circuits to be not fire resistant as long as sounder circuits were fire resistant, although most legitimate and competent installers had been wiring all FR for years.

After 2002 all new systems and any extensions or alterations to existing systems had to be in FR.

An existing system need not be upgraded unless a risk assessment determines otherwise, however it keeping non FR cable it's important to have the panel in 'Short Circuit = Fire' mode - this is why the use of non FR cabling used to be allowed as in the old days panels worked on a short creating a fire signal not a fault in case the detection cabling was damaged by fire before a call point or detector was operated. A modern panel will normally as default only give a fault on short (as all cabling is expected to be FR) but most decent makes can be set to SC=F for use on older systems.

[Guest Twin and earth used]

I have a old conventional unit looking to upgrade.  However the sensors and sounders are wired up to twin and earth cable.  It's large care home and to replace them to fp200 would be disruptive.  Can I just leave the twin and earth cable in place? Will it still pass the service inspections and regs. The cabling was installed in 1990s I think 

[AnthonyB]

Absolutely not and it didn't comply at the time of installation either and is exceedingly dangerous in a care home where evacuation is progressive and the integrity of the alarm system is critical.

The sounders should have been in FP as a minimum and the panel set to SC=F. If you are upgrading the system should be to current standards with full FP wiring.

A way to avoid disruption is to use wireless fire alarm technology https://www.safelincs.co.uk/wireless-fire-alarm-systems/