Security Light Wired Off 13A Ring Main

[macman81]

I've just discovered that the outside security light (a double spotlight with PIR) at the back of my house has been wired to the upstairs ring main. It's mounted about 12ft up the back wall and is supplied by a cable running off a double socket in the back bedroom, and then out through the wall.
I only found out because I had the downstairs lighting circuit off to do some other work, nipped out the back for a break and realised the light was still coming on.
The light itself is well up out of harms way but has a master switch just inside the back door. In order to make this safe what are my options please? To take a feed from the ground floor lighting circuit would involve a lot of destruction of decorations etc. All I can think of is to fit a switched FCU with a 3A fuse alongside the existing double socket and take the power from there.
Or is there another way of doing it?

 

[Lectrician]

Adding an FCU is the best option.

Is the switch in the kitchen possibly already an FCU?

 

[macman81]

No, I took a look, it's just a conventional one-way switch.
So could I just replace the existing switch with a switched FCU? But doesn't that mean that the circuit is still potentially allowing 13A up to the incoming side of the switched FCU? I thought that the FCU had to be on the supply cable rather than on the switch cable?
The ways it's been done is to run the switch cable from the light down the back wall in conduit, and then through the wall to the switch by the door. i.e. the switch is not wired in line, it's on a switch cable.
P.S. Just put the ladder up to check the rating of the security lights. They're only 120W each, so he can't have done this to avoid overloading the lighting circuit. It's just been done this way to get easy access to the supply.

 

[plugwash]

what size is the cable?

 

[macman81]

I'd need to double check in daylight, but it's either 1 or 1.5mm. Certainly not 2.5mm T&E.

 

[plugwash]

A switched FCU next to the existing socket does seem like the best soloution then.

 

[macman81]

What about Lectrician's point about swapping the existing switch for a switched FCU? Well, he didn't exactly say that, but that was what I inferred from it.
PS: I just rechecked the cable, the light is definitely wired in 1.5mm.

 

[macman81]

Can I just check one detail on this please? I'm now installing the FCU next to the double socket, must I use 2.5mm T+E to spur the socket up to the FCU, then OK to use the existing 1.5mm T+E transferred over to the FCU from the socket?

 

[plugwash]

Yes, 2.5mm from the socket to the FCU. The existing cable is ok after the FCU.

 

[macman81]

Thanks. I thought this would be a simple job but it's turning into a bit of a whodunit-or maybe a 'whowiredit'?
I took the front off the double socket that I assumed the light had been spurred from (because that socket is about a foot above and a foot to the right of where the light cable goes in through the back wall-the entry hole is just below 1st floor floorboard level). But that box contains only the ring main (2 cables). I then checked the other socket in that room which is another 3 ft to the right. Same thing-no spur cable. There are no other sockets on the back wall of the house where it could be spurred from. I rechecked and the light is definitely run off the upstairs ring main.
The only thing I can think of is that the spur has been run from a junction box under the floorboards before the ring main reaches the socket? Is this the only possibility, as I'd rather not take up the fitted carpet, floorboards etc to find I'm still wrong?
If I'm right, do I still correct this by rerouting it via an FCU?

 

[macman81]

Can anyone assist me with this please?

 

[MarkBarl]

As the switch is downstairs and it's powered from the Upstairs ring, is there a socket upstairs above where the switch is? It could be that they took the spur from there. Otherwise, it does sound like they tapped into the ring circuit with a JB. Have you got a cable detector that you could use to try to trace where the supply to the light switch comes from?

 

[ban-all-sheds]

But doesn't that mean that the circuit is still potentially allowing 13A up to the incoming side of the switched FCU?

Why do you think it would be 13A?

PS: I just rechecked the cable, the light is definitely wired in 1.5mm.

Is that the size of the cable running to the switch as well as from it?

But that box contains only the ring main (2 cables). I then checked the other socket in that room which is another 3 ft to the right. Same thing-no spur cable.

Have you actually checked that, i.e. you're sure that both of those sockets are on the ring, and that neither of them is already a spur?

The only thing I can think of is that the spur has been run from a junction box under the floorboards before the ring main reaches the socket? Is this the only possibility, as I'd rather not take up the fitted carpet, floorboards etc to find I'm still wrong?

It could have been connected anywhere.

One or both of those sockets could themselves be spurs.

It could have been done badly, it could have been done using who-knows-what bits of cable, it could be non-compliantly concealed somewhere - you won't know until you find the cable that runs to the switch.

If I'm right, do I still correct this by rerouting it via an FCU?

If you're right. But you need to know that you are, not hope.

 

[Veglen]

macman, you probably don’t want to hear this but my advice would be to roll a small area of the carpet back in the room above where the cable goes through the wall.

Re-lift the disturbed boards to locate the cable and follow it to its origin.

When the connection method and location have been found can you consider the correct and safe alternative!

V

 

[macman81]

Mark-no, the downstairs switch is in a single storey rear extension, no upstairs socket above that! Yes I have a cable detector, will try that, didn't think it would work though floorboards.
ban-sorry, I meant to say 32A. Yes, switch cable is all 1.5mm. Yes, sure both sockets are on the ring and not spurs, I did a continuity test on both to be sure.
Veglen-yes I know you're right, I was just trying to vainly convince myself there was another option.
As a stopgap, would it be any safer to replace the switch with an 3A FCU until I can get this sorted out?