I know nothing, but have a look here:
The wording of the description suggests that it could be used in the situation you describe. (I rather hope someone else, someone who knows something, comes along in a minute and agrees or disagrees.)
If you take your feed to the first alarm via a DP switch close to the CU, and then feed the switch from the same breaker as the lighting circuit then you can meet the requirement.
You could also do something similar from a ceiling rose position, again via a DP switch.
Subsequent alarms can be powered from the first via a 3&E that also carries the interlink signal.
It would meet the requirement for isolation, however it would also end up tucked into a ceiling void somewhere and hence would not be that convenient for maintenance purposes.
So thats an unusual bit of wiring around the CU then?..
Now what way do they want that done and what colour?..
Scary .. absolutely scary:(...
Hummmm.....
I don't think they have thought this out all that carefully...
Not especially - its not uncommon to provide isolating switches for all sorts of appliances of even clusters of appliances. For example you may have all your outside lights powered from the downstairs lighting circuit, but with an isolator that enables them to be independently turned off. As long as you label the switch, all should be clear. (in fact a keyswitch might be a good idea here)
The intention being that you can work on the alarm circuit and not have to turn off all the lights to do so.
Personally I would treat the interlink wire as a switched live[1] - much as you would treat the return from a switch. Hence flag it with brown sleeve on a harmonised colour 3&E, or red on a old colour one.
[1] Which for most alarms it probably is - although one should allow for the possibility that it may carry proprietary signalling with some brands of alarm.Seems to work ok for thermostats... ;-)
Why so?
We are doing a similar project and on certain doors have added electromagnetic catches linked to the detectors, so that the doors can be kept open but will automatically close if the alarm is triggered. The weirdest side effect is that the first indication I had of a day- time power cut was the sound of doors slamming shut.
Jonathan
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