Electrical wiring help

OK, I’m going to try and explain this one the best I can.

As most know, recently moved house and during the renovation they helpfully wired in cables by the front door for an external light.

Know here is where I get a little confussulded. There are two cables for a single light, now I think the term is switched live - but how do I wire it up?

Cable1 = Live, Neutral and Earth, currently is wired into the light which means the light is permanently ‘on’ (I say on - it has one of those light sensor/timers)

Cable2 = Live, Netural and Earth, and a little ‘SL’ written on it, which from chats to people down the pub mostly likely means switched live.

Just inside the door, there is a light switch that doesn’t affect any internal lights, so I am presuming this is the switch.

For those worried, there is a decent fusebox and when I turn off downstairs lighting I can work with no voltages :slight_smile:

So my question is - how do I wire up the switched live into the single terminal block that is in the actual light. I’m not going to pre-empt how I ‘think’ it should be done, I want to make sure first :slight_smile:

Thanks in advance, and yes I do have a multimeter if there is something that needs checking - and a few 9v batteries as well to test the cables with less risk :sneaky:


see if any of this helps…


a bit of gcse circuit diagrams and I think I’ve confirmed my instinct was correct, going to run through a little test with a 9v battery this afternoon.

I reckon, the cable marked SL is not connected to anything apart from the switch, so to add this switch to the circuit I need to connect the lives from the two cables together with a block, then connect the remaining cables into the light fitting, thus adding a switch into the circuit. To make it easier to visualise, imagine the second cable is a straight loop with only one colour cable through a switch. It all works then :smiley:

Ten minutes with the multimeter will confirm I think.


so u have 2 cables into the outside light? One of which is marked SL

Right… Connect the live of the permanently live cable to the neutral of the cable that feeds through to the switch backbox… and connect the switched live to the light fitting live terminal. And at the switch connect the switched live and neutral cores to the switch terminals.

It will work it you do what I say.

And I do have a bit of a grounding in Electrical circuits… I am an Electrical/Instrumentation Engineer by trade.:tiphat:

Fiend is right except with the wire colours. I’m not a domestic electrician but I think the two lives (Brown or red) should be linked in a block. Then the switch blue or black wire is live only when the the switch is on. The bulb goes between this and the feed wire neutral.
Oh and don’t forget to connect all the earth wires together and to any external metal.

I’ll be doing this this afternoon, thanks to all for comments. Quite pleased that I was right, although there is this discussion on colours but in all essence what does it matter, it’s a cable. In theory the switch wires should be a single colour, so a what goes into the switch comes out the switch :slight_smile: Well that’s my take on it anyway :lol:



Because then when the switch is off, the red (brown) wires are live and the black (blue) wires are at neutral potential. Less chance of expletives from your friendly neighbourhood sparky who often tends to work live :wink:

It would still work if you used the earth wire as a live conductor, but you wouldn’t do that now would you.

The Switched live section of the circuit is connected to the neutral circuit through the load (lightbulb)

Heres a handy diagram albeit for a light on a ceiling rose but the wiring should be the same.

do you reckon it’ll fail the test thingy and I’ll be prosecuted it I were to strip all three wires of the swith cable and put on some earth sleeving :lol:

So to confirm, I’ll go red-red ?


The biggest problem i had when doing this was that the house i am in has no earth coloured wiring! It has 2 blacks and a red (i think? or was it 2 reds and a black) so it took a bit of head scratching and making sure i labelled everything as i took it off to replace it.

2 blacks and a red thats “Crabtree Common” wiring or at least that is what we used to call it, that’s the one where its always live somewhere regardless of where the switch is set. Pull the fuse or breaker when you see that - as I found out years ago :slight_smile:

yeah, one other thing i recently found out, don’t just think that because the holes are in the same place on a replacement socket/fuse that they are the same! I managed to replace all the fused spur plates (went from white to brushed steel) and wired them up so that the sockets were still live even when the fused spur was switched off (hey, it’s not my fault there is no standard for holes on a socket wiring!)! My sparky mate wasn’t impressed when he came round to do some work and got a whack, needless to say, i was even less impressed when i got a whack from my mate also! :slight_smile:

Cheers Balrog…:tiphat:

Although my title is now E/I, I am basically a Instrument Engineer cross trained to on some electrical subjects (motors and such like). Tend to leave domestic wiring stuff to the electricians - too many regulations.

I think the is one of the rules you learn the hard way every time :lol:

The wiring in the factory i’m in now is nothing short of mysterious, the only way to be sure something is dead is to isolate the whole factory :eek:
Couple of months back we had a strange popping and fizzing sound in the middle of the workshop floor, every now and then a flash… pulled every fuse around it and it still was going… got brutal and hit the main isolator in the end. Turned out it was some old conduit running under the concrete floor, where it came up had had a hand full of cement put over it but that was letting water leak past so it had filled up with water, whatever was there originally, when it was removed they had just cut the wires and buried them. The wires lead straight back to the main buzz bar…

all done, working fine :thumbsup:

Now my ‘homing beacon’ has a proper on switch :lol:


But can to see it from the pub :wink: