Isolating smoke alarms

28 Mar 2009
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United Kingdom
I want to install two mains operated, interconnected smoke alarms (one on each floor). I don't have a free slot available on my conusmer unit so I want to connect them to the lighting circuit.

The 17th edition on-site guide says smoke alarms may be "supplied from a local, regularly used lighting circuit (there should be a means of isolating the supply to the alarms without affecting the lighting)".

Can anybody please give some guidance on how/where to isolate the smoke alarms? Surely you wouldn't want to have a switch somewhere that lets you turn off the supply? I though the whole point of wiring them into the lighting circuit was to prevent them from being switched off and forgotten about.

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A key operated switch in a prominent location and of the type where the key cannot be removed in the OFF position. Fix a large tell-tale to the key to ensure it can be seen as being in the switch.

Wire an emergency light with the supply to the alarms. This will then illuminate on its batteries all the time the alarms are isolated. Also useful if there is a total power failure when lights may be needed.
With emergency lights in some buildings the spec is to fit a neon next to the key operated switch. The switch would be a 2 way type, with one way feeding the em lights and the other the neon. The neon will be on when the lights are on test. This makes it obvious the switch is off.

An MK 2 gang grid yoke and front with a neon and 2 way key switch is what would typically be used.
Brilliant, this solves my problem. I hadn't seen the keyed switches before. I've searched on google and found some the the MK grid ones.

Thanks for the info!
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It's domestic, I'm refurbishing my 3 bed house. The electrical inspector from building control is coming around soon so I'm trying to make sure I do everything according to the regs.
Is this lighting circuit sharing sharing the same RCD as any of the socket circuits?
it's just you..

it's perfectly possible to rewire a house or do some electrical work and re-use the CU providing it's fairly new..

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