OP
accordfire
I just dislike the fact that any cable fault (open or short circuit anyhow) is going to render a whole zone of detection AND a sounder circuit useless.
About two years ago we got called by the local FO to look at a job in a care home to give an opinion as he wasn't certain it met L1 (!).
It didn't meet "L anything". Oh - the "system" we were looking at was the remains of one, in part, as the building had caught fire. There were around 9 or 10 detectors and three call points all on one twin wire zone with four maybe five G3 squashnis.
Critically, an oil fired boiler which blew up - no cut off on the oil, fortunately at the far end of the building so only took three rooms out - no loss of life, thankfully, but also turned out no FRA, un-maintained extinguishers (also inadequate number and wrong types), fire system woefully inadequate - 22 room home on single floor - one non-maintained emergency fitting stuck outside the front door (had been put in by the sparks when a recent porch had been built)....no maintenance on any of it - batteries in the panel were date stamped "Installed 03/2002".....company fitting it not identified.
That job today, is full L1 - conventional on a Haes Surveyor with Apollo heads - quarterly maintenance plus emergency lighting fully compliant, and extinguishers correct, and present. New owners, needless to say. That job was one of the first FRA prosecutions in this area.
Back to the twin-wire thing (admittedly it wasn't the fact it was twin-wire that caused the issue - more the fact that the owner at the time said it was what they could afford - while taking private rates in all 22 rooms!) .... for me, they have too many limitations for most systems, as the redundancy is built out of them - design becomes a very big issue with them, given that. As you say, a minimum of four zones - by which time, you're probably not saving that much cable over two conventional zones and two bell circuits..... (and don't get me started on 4 core PF lol).....
