"Steve" wrote in message
...

"rrh" wrote in message
. uk...

"thankyousam" wrote in message
oups.com...
I'm adding a couple of mains fed smoke alarms to my lighting circuit.
The first one is simple enough as there is a run of cable above the
location in the hallway. I'm intending to "loop in" the smoke alarm as
you would with a ceiling rose - allbeit without a switch

I'm not sure how to build the second alarm (upstairs) into the circuit.
Can I simply spur it off the downstairs smoke alarm using three+earth
(for the interconnect)? Or do I need to "loop in" the second alarm as
well? I've tried to illustrate both. I can't see why the first method
would be a problem, just wanted to check.

Spurred: ( = T&E, ||| 3&E Interconnect)

Rose ==== Smoke Alarm 1 ==== Rose
|||
|||
Smoke Alarm 2

Full Loop In: ( = T&E, =~= 3&E Interconnect)

Rose ==== Smoke Alarm 1 =~=~= Smoke Alarm 2 ==== Rose


You can just spur it off the first alarm.

That's a bit dodgy innit? If your lighting is set up as one circuit to
cover the whole house, it may be OK but if the downstairs lights are on
one fuse and the upstairs lights a different fuse, someone could pull the
fuse for the upstairs and expect the smoke alarm to be safe to work on
when it's not.

Steve.


Can't lay my hands on the regs just now but they insist that interconnected
alarms are wired to one circuit only. Mains-powered alarms without battery
backup ("Grade E") should have their own dedicated (and preferably
non-RCD-protected) circuit from the consumer unit; mains-powered alarms with
battery backup ("Grade D") may be wired either that way or to a regularly
used local lighting circuit that is separately electrically protected.