Quick sense check of this lighting circuit

[uptown47]

Just wondered if someone could cast an eye over this lighting circuit and make sure I'm approaching this correctly. I want to run my smoke alarms from my lighting circuit. I also want a neutral at the switch so that I can upgrade to 'smart' switch in the future.

I'm going for the "two plate" method and using all 1.5mm T+E.

I realised that if I went to the switch first then I couldn't go to the light, the next switch AND the alarm. So I thought I would run from the CU to the first smoke alarm then back to the light switch then to the lights and the next switch... as per the drawing below.

Can you see anything wrong with this?

Thanks for casting an eye over it for me (and excuse the basic drawing.... hopefully it'll make sense).

 

[flameport]

That could work, but the smoke alarms also need an interconnect wire, 3C&E would normally be used for that.

I realised that if I went to the switch first then I couldn't go to the light, the next switch AND the alarm

Why not?

 

[uptown47]

That could work, but the smoke alarms also need an interconnect wire, 3C&E would normally be used for that.


Why not?

Thanks for that. The alarms are connected via RF so don't need a hardwired connection thanks. The reason I didn't think it was possible was just due to the lack of room in the switch box. Didn't want a separate junction box as it would need to be "accessible" according to the regs from what I understand so couldn't stash it in the ceiling void.

That's why I thought try and keep a maximum of 3 cables in each switch box.

Please correct me though if I'm wrong. Many thanks

 

[Adam_151]

You 'could' do it like that, but I wouldn't. I'd put a three core between the smokes even if you plan to use RF ones, just incase you have problems with the RF link with interference or signal being blocked etc, maybe not likely but it gives you a fall back after the decoration is finished! Personally I'd run a separate leg in 1mm twin to the first smoke detector and then 3c 1mm to the next, they can still be one cirucit at the board if thats what you want, you'd cause yourself unnecessary trouble looping 1.5mm through most smokes (yes it'll go, but its tight in many brands), you might as well use 1mm for the lighting leg as well, its most unlikely you actually need 1.5

 

[TimboTwo]

As pretty much all lights these days are LED, there isn't any need to use 1.5mm², 1.0mm² is ample (and cheaper). Add up the load and see. If looking to use smart switches, fit 35mm deep boxes to allow plenty of room for them.

 

[uptown47]

You 'could' do it like that, but I wouldn't. I'd put a three core between the smokes even if you plan to use RF ones, just incase you have problems with the RF link with interference or signal being blocked etc, maybe not likely but it gives you a fall back after the decoration is finished! Personally I'd run a separate leg in 1mm twin to the first smoke detector and then 3c 1mm to the next, they can still be one cirucit at the board if thats what you want, you'd cause yourself unnecessary trouble looping 1.5mm through most smokes (yes it'll go, but its tight in many brands), you might as well use 1mm for the lighting leg as well, its most unlikely you actually need 1.5

Really good points! I will run it as you say. Probably going to stick to 1.5mm though as I've got a 100m roll of that so got plenty. I watched a YouTube video on the FireAngel range and the guy on there got two 1.5mm cables into the alarm okay so hopefully I won't have a problem - maybe just tight as you say. Thanks for your great advice

As pretty much all lights these days are LED, there isn't any need to use 1.5mm², 1.0mm² is ample (and cheaper). Add up the load and see. If looking to use smart switches, fit 35mm deep boxes to allow plenty of room for them.

That's a brilliant point about the 35mm back boxes - glad you mentioned it. I'll speak to the joiner and make sure I'm not going to be left with any 25mm boxes. Thanks