Hi trust you are familiar with bs5839 pt1/6 and have training cert. cause if not your P/L insurance won't cover you!
If you 'design' the system you need design liability cover, and if fire occurs & for any reason alarm fails to operate correctly you need 'Efficacy' insurance or you become liable for cost of ALL loses!
Sorry to lay that on you but NAPIT/ECA etc insist on such cover if you do Fire/intruder alarms, for your own protection.
It costs a bit more on your yearly overheads but is really worth it, amazing how many leckies are under insured.
However in answer to your post 4 wires are simply 2 for detectors and 2 for sounders which can be either run seperately as 2X2core &cpc or as 1X4core& cpc if 'stacking' detectors on sounder bases.
All wiring must be in Flameproof low smoke cables such as FP100/Firetuf etc.
Not sure about '3Wire system' you refer to, not in this century anyway.
As for 2 wire combined systems where both sounders and detectors share same pair of wires YUCK! nice idea but rubbish equipment imho will never install anymore.
Only 2 wire system any good is addressable type which are ok until it needs extending later, need reprogramming etc, hassle,
good luck Sparx
I did mine at Crawley college which is part owned by ECA and was available at short notice, (maybe it was quicker as a member).
Lots of 'colleges' advertise in 'Professional Electrician' mag, don't know what courses who offers though, must say I haven't noticed any Fire alarm or emergency lighting ones of late.
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