Smoke detectors Wiring

Joe100w · Posted: Sun Apr 05, 2009 3:32 pm Post Subject: Smoke detectors Wiring

I am fitting two smoke detectors. One upstairs and one downstairs. Also I am putting a heat detector in the kitchen.

These will be on their own circuit without RCD.

1) Should I interconnect all of them?

2) Should I have two dedicated circuits - 1 for upstairs and 1 for groundfloor.

3) Planning to use Type B 6 A MCB

Would like your knowledgeable views.

Cheers.

breezer · Posted: Sun Apr 05, 2009 4:07 pm Post Subject: Re: Smoke detectors Wiring

Joe100w wrote:

1) Should I interconnect all of them?

depends on the make / model

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RF Lighting · Posted: Sun Apr 05, 2009 4:14 pm Post Subject:

Will any of the circuit wiring be concealed within a wall or partition at a depth of less than 50mm?

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wingcoax · Posted: Sun Apr 05, 2009 4:43 pm Post Subject:

Taking what RF said into consideration, Yes you should interconnect them, that way when one goes off they all go off so you dont miss the noise.
If you have a spare way in your CU then yes you should wire through their own mcb.

flameport · Posted: Sun Apr 05, 2009 4:47 pm Post Subject:

One circuit for all. 6A will be plenty (even with 3, the total current will be far less than 1A).
Interconnect all of them (providing they can be - get another type if not)
Heat detector in kitchen, Optical detector downstairs, Ionisation detector upstairs. All of the type with backup batteries.

2core + earth from CU to the 1st detector. 3core + earth between the detectors.
With the 3 core, Black = interconnect. Grey = neutral (with blue sleeve). Brown = Live.

No RCD on the circuit if possible. If the cables can't be concealed more than 50mm deep, use BS8436 cable such as this.
If you must have an RCD on it, connect them to a lighting circuit so that if the RCD trips, people will notice.

Joe100w · Posted: Sun Apr 05, 2009 4:50 pm Post Subject:

wingcoax

Yes I have two spare connection in the Consumer unit.

The wire is running in the ceiling spaces downstairs and up airing cupboard to loft for upstairs.

Have not bought the actual detectors yes and the wiring is sort of there but not finished yet.

Thanks

sparkyspike · Posted: Sun Apr 05, 2009 7:53 pm Post Subject:

If your smoke alarms are interconnected with battery back-up, then I would wire the circuit into an RCBO on the non-RCD side of the CU. The alarm will tell you if it is low on battery or has no power and the power will only be interrupted if there is a fault on the smoke alarm circuit. If you put the alarm on a shared circuit or common RCD, then it can lose power when there is a fault elsewhere.

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Eng33 · Posted: Sun Apr 05, 2009 8:03 pm Post Subject:

Very useful thread, answers just about all the Q's I had on the subject...

flameport wrote:

One circuit for all. 6A will be plenty (even with 3, the total current will be far less than 1A).
Interconnect all of them (providing they can be - get another type if not)
Heat detector in kitchen, Optical detector downstairs, Ionisation detector upstairs. All of the type with backup batteries.

2core + earth from CU to the 1st detector. 3core + earth between the detectors.
With the 3 core, Black = interconnect. Grey = neutral (with blue sleeve). Brown = Live.

No RCD on the circuit if possible. If the cables can't be concealed more than 50mm deep, use BS8436 cable such as this.
If you must have an RCD on it, connect them to a lighting circuit so that if the RCD trips, people will notice.

Only other I have is can you recommend a brand(s) of interconnected smoke detector? Would prefer a low profile / slim type.

Thanks.

flameport · Posted: Sun Apr 05, 2009 9:36 pm Post Subject:

I normally fit these ones:
http://www.tlc-direct.co.uk/Main_Index/Fire_and_Smoke/Smoke_Alarms_Mains_Lithium/index.html

Not the cheapest, but they have a 10 year warranty and no batteries to replace, ever.

As for low profile - probably doesn't exist. They have to be where air can circulate, otherwise they wouldn't work.

Eng33 · Posted: Sun Apr 05, 2009 9:44 pm Post Subject:

flameport wrote:

I normally fit these ones:
http://www.tlc-direct.co.uk/Main_Index/Fire_and_Smoke/Smoke_Alarms_Mains_Lithium/index.html

Not the cheapest, but they have a 10 year warranty and no batteries to replace, ever.

As for low profile - probably doesn't exist. They have to be where air can circulate, otherwise they wouldn't work.

Many thanks. Just realised the extra depth comes from the additional pattress, but not necessary if wiring access from above - which I do have (bungalow).

flameport · Posted: Sun Apr 05, 2009 9:47 pm Post Subject:

If mounting direct to the ceiling, fit a single gang dry lining box into the ceiling (this is where the wiring connectors go), and the detector then fixes to the dry lining box.

bongos · Posted: Mon Apr 06, 2009 10:37 am Post Subject:

When wiring smokes and lighting circuit, is it acceptable to go to the smoke alarms first and then continue onto the lights with a L/N/E from the last detector?

flameport · Posted: Mon Apr 06, 2009 8:41 pm Post Subject:

bongos wrote:

When wiring smokes and lighting circuit, is it acceptable to go to the smoke alarms first and then continue onto the lights with a L/N/E from the last detector?

Probably no regulation to prohibit that (perhaps the one about dividing an installation into separate circuits?) , but seems a shoddy way of doing it. If you are installing cables in for a new smoke alarm circuit, its no extra effort to pull in another T+E at the same time.