Twin wire fire alarm.

[Tom Sutton]

How do you make a twin wire fire alarm (http://www.assured-ltd.co.uk/fire-protection/fire-alarm-systems/twin-wire-fire-alarms/) conform to BS 5839:1 especially clause 12.2.2 (j) system integrity?

[Bill J]

Twin-wire systems are quite common, albeit by many names.

They are non-addressable systems, which have Callpoints and Detectors on a radial circuit acting as the triggering circuit.

Once the Zone has activated, the same cable is then used to activate sounders.

So the trigger devices and fire alarm devices are on one circuit (per zone), so one fault only affects one circuit.

As long as more than one zone containing trigger devices AND sounders is installed, then 12.2.2 (j) is satisfied.

Most Twinwire type panels also have separate sounder circuits, although rarely used.

I hope this makes sense.

Bill



 

[Tom Sutton]

Thanks Bill, I was asked does a twin wire fire alarm conform to the BS 5839 in relation to clause 12.2.2 especially (j) which says "In the event of a single open circuit or short circuit fault on any circuit that serves the fire alarm sounders, at least on single fire alarm sounder, normally located in the vicinity of the CIE, should still sound correctly if a fire alarm condition occurs anywhere within the building."

I was a former artist in burnt clay not a sparky so I told him I could not help him, but I am interested and would like to find an answer.

The way I read it, is if there are more than two radial circuits and at least two of the circuits have the first device, a sounder located close to the CIE that would comply. Also if there is a dedicated sounder circuit and only one sounder is fitted close to the CIE,  followed by as many radial circuits as you chose that would comply.

I am sure there are more configurations especially if you use ring circuits but, if this is correct then that is all I need to know.

[AnthonyB]

The kit easily complies - as long as the installer has a clue!

I surveyed a site with a proper fire alarm engineer as the RP was worried their general spark had done a half job and almost all the systems (which were standard 4 wire panels) all having 1 sounder circuit and one unit fitted out with part 6 Grade D kit located such that they might as well have not bothered!