smoke detector wiring

[Niel A. Farrow]

HI, the TLC web site says that SD's with battery back-up can be powered from a a lighting cicuit rather than a dedicated circuit. It also says that interlinked SD's have to be on the same MCB/fuse circuit.

So, do I;

1. insert a junction box into a nearby lighting circuit power cable
2. run a cable from this jn box (1) to another jn box (2)
3. connect L, N and the interconnect wire of SD to jn box 2, and terminate E
4. connect 3 core and E to N, L and interconnect in jn box 2, and run this to the next jn box and SD (and not use the E)

Is this OK or does each SD need its own power supply. The instructions were a bit vague.

Thank you, Neil

[Frisket]

Yeah, looks about right although if you fit "fastafix" boxes in the ceiling you can do without the jb's as the smokie backplates will screw straight to them. HTH, Richard

[Christian McArdle]

They do have battery backup. You can get types that don't, but they are rare, not recommended, and require special installation techniques, like having their own way on the consumer unit.

Christian.

[David W.E. Roberts]

Confused now.

You said

"It is safer to connect to a light circuit than have a dedicated one. This is because the MCB tripping is more likely to be noticed as the lights would stop working. A dedicated smoke detector circuit going down is unlikely to be detected for weeks."

but if the smoke detector circuit has battery backup and chirps of it loses mains power then how can it go undetected for weeks?

Unless it only chirps when the backup battery is going flat.

In which case modify my query to "Why doesn't it chirp straight away? Or at least after 30 minutes or so to cover temporary off/on scenarios?"

Cheers Dave R

[Andrew Gabriel]

I suspect that after a 3 hour power cut, no such smoke detector would still be intact and working ;-)

[Gel]

AC Only alarms are not that rare, though majority sold are type with battery back up either loose battery or sealed in Lithium.

AC only are cheaper but are useless in power cut. They also under Bldg Regs must be wired on separate spur on consumer unit.

Those with battery back up can be taken off adjacent unswitched lighting circuit.

There are wiring diagrams on this web site; download "installers" pdf.

TLC sell this brand too

ww.tlc-direct.co.uk

[Gel]

[Toby]

The detectors I've fitted are mains/battery, a regular replaceable 9v alkaline. The battery is not charged, it's used as an alternate supply. You can see a green led if the mains is healthy, once a minute a red led flash shows the battery is OK. It chirps when the battery is nearing exhaustion. You don't really notice the leds except at night. If it chirped at a loss of mains then they would not be fitted! as the whole house rewire is going a bit slowly.