splitting cables

[sarebearmeeks]

I have a new spotlight bar that has earth, live and neutral connections but my ceiling wires have 3x red, 3x black and 2xgreen/yellow cables coming from it, which one do I put in the new light and what do i do with the others? thanks

 

[plugwash]

ahh removing light fittings without noting down the connections: this should be on the list of most common newbie mistakes

one of your cables brings in power

one takes power out to the next light

the third one runs to the switch.

the reds of the three cables should be joined together but not joined to the light

all green/yellow wires go to the earth terminal of the light

the blacks of the wire from the mains and the wire going to the next light go to the neutral terminal of the light fitting.

the black from the switch (which should be sleeved red but often isn't) goes to the live terminal of the light.

if one of the blacks is sleeved red then this is almost certainly the switch cable and you can proceed as above.

if not then you have the problem of identifying which wire is which. Whilst not at all difficult for someone reasonablly familiar with a multimeter this is a bit tricky to explain to someone who knows almost nothing about electricity.

 

[sarebearmeeks]

Great thanks, I haven't dismantled the wires yet wanted to check first so I will go home and check the wires and get back to you.(no access to internet at home I'm in a cafe!) Don't worry I won't do anything until I'm absolutely sure I don't want to die!

 

[Panjandrum]

Don't worry I won't do anything until I'm absolutely sure I don't want to die!

Until you are sure absolutely sure you don't want to die, it would probably be best if you were to stay put in the cafe.
Sorry to point this out, but the occasional bit of overlooked punctuation brightens my day - thanks.

 

[felix]

Unless somebody has seriously mis-wired your light fitting, Plugwash has correctly identified the functions of the wires in it. Here's the extra bit of information you need:

1) The earth terminal will be obvious and will never be live.

2) The terminal with three red wires in it will always be live whether the switch is on or not.

3) The terminal with two black wires and one old light wire (if still present) will never be live. It's the neutral line.

4) The terminal with the single black wire and the the other old light wire will be live only when the switch is on but there's a catch here. Because of capacitive coupling across the switch cable, most meters will show some voltage on this terminal if there is no light fitted. Neon screwdrivers will also glow but not as brightly as they do on the live terminal.

You will see that you need some means of checking for live terminals, namely a meter or a neon driver - and I mean a proper mains rated neon driver with an insulated blade, not some cheap piece of junk off a market stall.

And since you're new to electrics, here's a some valuable advice for working on live circuits:

1) Don't do it unless you can't avoid it, as in this case.
2) Wear rubber soled shoes.
3) Always be aware of what your other hand is doing. Holding onto earthed metal with one hand while you prod around a live circuit with the other is a really bad idea. The best place to put it is in your pocket.

Perhaps I've put you off the whole measurement business. In that case try this. Isolate the circuit at the fuse box and connect a simple, two wire bulb holder between the single black wire (switched live) and the paired black wires (neutral). Put a bulb in it then switch on at the fuse box. If the wall switch controls this light correctly then you have the right pair of terminals for your new lights. Nothing nasty can happen, even with the most diabolically mis-wired circuit, though you might get some strange effects, like the light won't come on/go off or it comes on dim and so do some others. If anything like this happens I suggest you get an expert in to sort the whole mess out.

Assuming that the test goes well, connect the brown wire(s) of your new lights to the switched live terminal (single black remember), blue to neutral and green/yellow to earth. Needless to say you do all this with power off.

 

[sarebearmeeks]

Ok I have isolated what is what, the cable from the previous light, the next light and to the wall switch. There are three wires in each cable, one black, one yellow and green and one black. One of the black wires is the 'live' one but is not tagged but was fed into the switch terminal on the ceiling rose. With the new light fitting am I right that this 'live' black wire is to go into the live terminal block and the other two black wires into the neutral and all three earths into the earth terminal. this leaves the three red wires which I was advised to leave, how should I leave them, i.e taped with insulation tape?

 

[plugwash]

the three red wires need to be connected to each other.

a piece of chock block is the usual way of doing this.

 

[sarebearmeeks]

Hi there thanks for all yr help, sorry to go on i just want to double check everything i do before I do it! What is chock block? Is it what was originally holding the wires in the ceiling rose? I take it i cannot just strip and twist the wires together? Also can you please confirm that i have the right wires going into the right places (assuming that I have the right wires to begin with) Black'live' into the live socket, 2 x black wires from the (previous and next light) into the neutral and then all three earths into the earth plus the three red wires not attached to anything but each other. thanks for yr help

 

[eswdd]

choc block = connector block

see also the sticky topic in this forum, there is a pic on page 2 or 3

 

[sarebearmeeks]

page 2/3 where?!

 

[eswdd]

top of the electrics uk forum is a sticky "for reference" topic. on page 3, post 4 is a piccy, also here: //www.diynot.com/forums/viewtopic.php?t=7553&postdays=0&postorder=asc&start=30

 

[securespark]

1) The earth terminal will be obvious and will never be live.

2) The terminal with three red wires in it will always be live whether the switch is on or not.

3) The terminal with two black wires and one old light wire (if still present) will never be live. It's the neutral line.

1). Until there is a fault condition.

2). Unless the fuse has blown or been removed, or the mcb tripped.

3). Unless you split them with the circuit live, and a light on elsewhere.

 

[ban-all-sheds]

I take it i cannot just strip and twist the wires together?

No - you must never do that.

 

[felix]

First off, my thanks to securespark. My three comments were based on everything being wired up and working correctly; something which I know is not always true. I'll choose my words more carefully from now on, eg "these SHOULD never be live". I once worked on a house where the neutral return from the upstairs lights went to the downstairs circuit and vice versa. I had the downstairs fuse out and my trusty neon showed all wires dead. Then I separated two neutrals --- Moral: never trust anybody else's work. Test, test and test again.

To sarebearmeeks: You're nearly home and dry. Those three remaining red wires must be connected to each other or not only will your new light not work but quite a few others won't work either. Chocolate block is quite cheap. You get it in a long strip from any electrical shop and cut off what you don't need - in this case most of it! It does come in different sizes so get some big enough to hold all three wires in the same hole. Incidentally, I like to put all the wires in from the same side and use both screws on them.

 

[ban-all-sheds]

my trusty neon showed all wires dead.

Here's another moral for you - never use a neon tester for anything other than turning screws....