3 core smoke alarm to 2 core outdoor lighting

[wingy1978]

hope someone can help.

I am installing an outsire pir dusk dawn light which is 2 core and earth.

I am connecting it up in the loft and cant connect to a bedroom light as there is no continual live feed to it or switched circuit.

I have 2 smoke alarms 1 downstairs and 1 upstaire. I have found the cabling and cut the cable. it has a black brown eart and grey cable.The outdoor light is brown and blue. I assume the brown goes to brown and blue goes to grey I guess but this didnt work.

Can anyone help me with this. sorry

 

[electronicsuk]

If this is a dedicated smoke alarm circuit then feeding outside lighting from it is a bad idea full stop, and you should probably undo the damage you've already caused and find somewhere more suitable to take the feed from.

If the smoke alarms are already part of the lighting circuit, it will be a simple job to take the cover off one of them and identify which colour conductors do what.

 

[flameport]

What the core colours are depends entirely on the person who installed the smoke alarms. The only way to find out is to examine the connections at the start of the circuit, or the previous smoke alarm.

However:
- fixing an outside light to a smoke alarm circuit is a bad idea
- you have now disconnected your smoke alarms, so when there is a fire, they won't work
- by randomly connecting the smoke alarm cable to the new light you may have damaged it, or the smoke alarms, or both.

If you have lights on the upper floor of your house, how can there not be anywhere in the loft to connect an additional light?

 

[wingy1978]

All the lights on the top floor only have 3 cables going into the rose, earth live and neutral.

I do have an extractor fan switch in the top of the wall for the bathroom which i assume the cable goes into the loft. could I tap into this.

I have allready fixed the mess I made with the smoke alarm and all is good now thanks. just confused sorry normally i only replace whats there not add something to a circuit

 

[electronicsuk]

All the lights on the top floor only have 3 cables going into the rose, earth live and neutral.

Then it's probably been looped at the switch or using junction boxes, but the wires will still very likely appear in the loft somewhere. You just need to trace them back...