Wiring connections - Smoke and heat alarms

20 May 2009
Reaction score
United Kingdom
Hi. I intend to install a selection of ionisatio and optical smoke alarms and a heat alarm. They will be Kidde mains interlinked alarms on a dedicated circuit from a consumer box.

The alarms all come with three short (10 inch) soldered electrical tails viz. positive, negative and white interlink which will be interlinked using 1mm flat 3 core cable. All alarms will be ceiling mounted and accessible from the floor above except for one which will be a beneath a flat roof cavity but can still be accessed through the ceiling.

I should be very grateful for any comments, suggestions, etc re the following questions please:

First relates to the interlinking between the alarms. Can I connect the three tails to the flat cable using "chocolate" connections or are there better alternatives?

Secondly, I understand the link from the consumer box and the first alarm in the series should be three core but in this case 2 core plus earth. As there is no actual earth connection, I am puzzled by the purpose of the earth lead.

Many thanks in anticipation of your assistance
Sponsored Links
Use 3 core and earth for all the interlinks - keeping the earth continuity all the way through to the last one.
You can purchase 3c+e this in red for this purpose.
Twin and earth is acceptable for the CU to the first smoke head but if you buy a roll of 3c&e in red use that - sleeve the black with earth sleeve and double it up with the CPC. Sleeve the grey with blue sleeve and use that as neutral.
Sleeve the blacks used for the interlinks with brown, the grey used as neutral needs sleeved blue.
If there are any cables concealed in a wall or partition then you will need to ensure the circuit is RCD protected, but not on the same RCD as a socket circuit.
You can use terminal block if you like, you can often buy a base with a piece of terminal block in it already.
Whichever method you use you need to have the terminals in some sort of enclosure.
This work will be notifiable to your LABC under part p of the building regs if you live in England/Wales.
The correct way to fit those alarms is:
1. Fit a single gang dry lining box into the ceiling
2. Get a length of 15A terminal strip and cut of a piece with 4 connectors
3. Join the incoming and outgoing cables using the terminal strip. (L/N/E/Interlink). Use the black core as the interlink, and the grey core as neutral (with blue sleeving over the end). Green/yellow sleeve over the earth as usual.
4. Connect the supplied wiring harness to the terminal strip
5. Fix the alarm mounting plate over the dry lining box
6. Test the circuit
7. Connect alarms to the wiring connector and clip onto the mounting plate.
Don't sleeve the black with brown for the interlink. It is not a mains voltage interlink (it interlinks as an ELV signal so it can still interlink during a power failure). ELV control signals are black, so the black can be left unsleeved.
Sponsored Links
The NIC don't write the regs tho ;)
I still don't see why it is wrong to do that - it isn't as if the link wire is being used for an ELV application (if anything FELV - you wouldn't want to touch it in use!), it is mixed in amongst mains voltage conductors.
Many thanks everyone for your very interesting and helpful comments.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links