Wiring Into a Lighting Circuit

[Oskool]

I’m trying to wire up a garage alarm which I want to have in the middle of the ceiling next to a light fitting. I’ve tried to connect the wires to this circuit but the alarm only comes on with the light switch (not good if a burglar has a torch).

Is there a way to do this so it stays permanently on?

There are three red wires together an earth wire and two lots of two black wires together (one with insulation tape round it).
The cable on the alarm has the standard blue, brown and green wires.

Any help would be much appreciated.

 

[Gaz the Sparky]

Connect the brown core to the three reds these will be permanely live

Connect the blue core to the blacks without tape on

Connect the green and yellow to the green and yellow

GTS

 

[Oskool]

That’s how I thought it should be but it still turns on and off with the light switch?

 

[Oskool]

Is there a way of getting it working?

 

[JohnD]

Go up to the High Street and buy yourself a multimeter for about £8, then report back and we'll tell you how to find the Permanent Live and Neutral.

 

[Oskool]

I have a multimeter, what do I set the dial to?

 

[JohnD]

AC Voltage. A range that includes 250v.

If you are working at the ceiling rose, turn off the light switch and try from each terminal that holds Red, against each terminal that holds black.

It will usually be the terminal that holds 3 red, and the terminal that holds 2 black.

You will find there is a permanent (unswitched) live and a permanent neutral. this will give you the unswitched supply that you need.

If the lamp does not have many wires in it, there may be a junction box somewhere else' perhaps at the ceiling hole, maybe hidden between the ceiling and the floor or roof above.

You mention the old light fitting has taped up wires. If you buy a new modern ceiling rose (or junction box) it will usually have plenty of terminals where you can put all the sets of wires neatly. Before taking any wires out of the old connectors mark or number them so you you can re-connect them in the same pattern (this is very important).

 

[Oskool]

Thanks for your help John, I’ve just tried it on both sets of black wires and there is no current showing on the multimeter when the light is switched off. It shows only when the lights are switched on.
Does this mean that there is no permanent live?
Like you said there is a connector block with 3 reds in it, another connector block with two black, and another connector block with two black wires.

 

[JohnD]

just to check, you have tried it with one test prong on the reds, and one prong on the blacks? And no voltage? Even against the taped-up blacks?

Can you try your tester on a known live point to make sure it is indicating correctly?

 

[Oskool]

just to check, you have tried it with one test prong on the reds, and one prong on the blacks? And no voltage? Even against the taped-up blacks? Yes that right John

Can you try your tester on a known live point to make sure it is indicating correctly? I've tried it with the light switch on and it shows voltage, would that be ok?

 

[JohnD]

Then I'm sorry, I don't know.

Try to trace the cables back and see where they pick up their current.

Also have a look behind the switch(es) and see if there is more than one red and one black there.