Electrical wiring of a light

[B3any]

hi, I have a problem with the wiring in my kitchen. This weekend I attempted to wire up a new light fitting which I bought from Ikea, I think that might be the problem! I took down an old flourescent tube, and didn't pay attention to the wiring configuration and that's where the problems begin. I have 3 cables running to the light fitting in the ceiling. I wired it up all the lives to the live and all the neutrals to the neutral turned on the power at the fuesbox and the light came on, result! When I came to turn it off the circuit breaker went pop. So I played around and it kept going pop. I numbered the three cables,

1+2 light goes on and stays on, doesn't matter what I do with the switch it stays on. 2+3 Light stays off 1+3 circuit board goes pop. following constant frustration I now find that my bathroom light doesn't come on, it must be a spur off the kitchen light Can anyone give me an insight into why I can't turn my light off, and why the system keeps tripping. Cheers Nick

[Bob Mannix]

Yes, you wried all the reds together and all the blacks together.

This mean the light switch, when off, does nothing. When on it sorts live to neutral. You are lucky that the switch contacts haven't fused together (lucky in the sense you don't have to buy a new switch).

One of the cables goes to the switch. All the reds (including the switch one) are connected together. All the blacks, *apart from the one from the switch*, are connected together. The blue from the light connects to the common blacks. The brown from the light connects to the black from the switch. The black from the switch should have a red sleeve on it but probably doesn't.

[Dave Plowman (News)]

This is probably the most common thing idiots do. ;-) Those with knowledge and respect for wiring note where things went. And if you had, you'd not be asking this question. ;-)

Basically, think it through. What do the three of cables do?

The common answer is one is power in, one is power out to the next fitting, and one goes to the switch. And the switch shorts across that cable when on. Thus tripping the circuit if wired incorrectly.

So the first thing you need to do is identify which one is the switch cable. Easiest way is with a DVM using the continuity or resistance measurement. With the power off, connecting the meter between the correct line and neutral of the switch pair will show a short with the switch on, none with it off. Mark the neutral of this pair preferably with a red sleeve if the colours are red and black, or brown if they're brown and blue. Connect this cable to the *line* of the fitting. Both the other neutrals are connected together and to the neutral of the fitting. All three lines are connected to each other but not to the fitting. All the earths should be connected together and to the fitting if needed.

[John]

Try this:

need to identify which wire should have a red sleeve on it. (often missed)

[David Hansen]

On Mon, 30 Jun 2008 02:36:00 -0700 (PDT) someone who may be B3any wrote this:-

A fairly common mistake, which it is best to learn from.

Playing around is not a good way to work out what is happening. Far better to test it properly and work out which wire is which.

Others have answered this. Hopefully you have now been able to sort out the problem.

It keeps tripping because the protective device is doing what it is supposed to do. Cure the fault which you have introduced into the wiring and I imagine it will stop tripping.

[Martin Pentreath]

Hi Nick,

Many of us (certainly me) started our understanding of domestic wiring by getting equally confused about the wiring of ceiling lights, and then having it explained to us by some helpful person/website. One of my many mistakes was to take off all the three-way switches on my staircase, smugly write down the connections on a bit of old paper (there's one extra colour to add to the possible permutations), and then lose it. Even after I worked it out again I still can't say that I understand three-way switching.

Cheers!

Martin

[George (dicegeorge)]

draw a wiring diagram using lots of colours not black and white...

and get a book out of the library

[g]

[EricP]

And don't lose the bit of paper, because...............that can be very embarrassing!

Not that I have ever done that of course!

[John Rumm]

Oddly - it won't help. Chances are it has three connections - one live, one neutral, and one earth. You need 4!

1) A permanent live this connects the live in (from previous light), live out (to next light) and switch feed together. *Note that it does not get directly connected to the live on the lamp - or you won't be able to turn it off* 2) You also need a neutral connection for neutral in and out (you can use the one on the lamp for this) 3) you need and earth connection (ditto - join all earths together using the supplied terminal) 4) and you need switched live. This is the (probably black) wire that comes back from the switch - connect this to the live terminal on the lamp.

[Dave Plowman (News)]

L1 L1 0===========0 0===========0============= Line | \ / | C 0================================O C \ / \ / 0===========0 0===========0============= Switch return L2 Optional L2 Intermediate

[John]

Is "3 way" correct terminology? Isn't it still 2 way - with an intermediate switch? If you added 3 intermediate switches - would you call it 5 way?

[Martin Pentreath]

Don't know what the official answer is, but what's the "two" in two- way referring to if it's not the number of switches involved??

Thanks Dave for the diagram, I remember studying something like it at the time, and still not feeling much wiser, although it helped to get it working. I don't think I was cut out to be an electrician.

[John]

The switch has 2 outputs from one common.

[jgharston]

=3D=3D=3D=3D=3D=3D=3D=3D0=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Line

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3DO C

=3D=3D=3D=3D=3D=3D=3D=3D0=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Switch retu= rn

It's three *point* or *location* switching. A switch in three different locations. Each switch still only switches to *two* positions, or ways. The confusion arises because with a two-point switching circuit you use two two-way switches, and so everybody ends up calling it "two-way switching".

This is why, whenever I have the opportunity, I replace any combined outlet & junction wiring with a seperate junction box with a single cable to the outlet.

-- JGH

[John]

It's three *point* or *location* switching. A switch in three different locations. Each switch still only switches to *two* positions, or ways. The confusion arises because with a two-point switching circuit you use two two-way switches, and so everybody ends up calling it "two-way switching".

This is why, whenever I have the opportunity, I replace any combined outlet & junction wiring with a seperate junction box with a single cable to the outlet.

-- JGH

A good idea - but access is often a limitation - and you are also introducing additional connections (which could loosen). I don't like the design of junction boxes - they seem stuck in a "design time warp"

[Dave Plowman (News)]

Basically, each terminal on the switch is labelled as I've shown and all you have to do is connect those terminals as in the diagram. Same way as you'd wire up a plug. Hopefully.

[cj]

We ancients were taught like this if it helps. a switch interrupts a circuit and can be used to disconnect said circuit or change its path to a different location or WAY. Switches can be grouped together to form GANGS. So a 1 way switch can only stop or start flow in 1 WAY whist a 2 way switch can change flow to 2 different WAYS and a 3 way 4 way etc whilst 2 switches together in the same housing are a 2Gang switch and 3 a 3 Gang.

As for the lighting circuit as there is only 1 common source of output the circuit is 2 way with intermediate switching as the extra switches are intermediately placed in the circuit and can be numerous.

Memories of a question posed by my instructor years ago.Regarding a lighthouse.(but that's another thread)

Seems they may teach the theory differently these days but the outcome is the same .(you can switch the light on or off from various points.)

CJ

[John]

Excellent (although when two way switches are grouped on a plate as a 2 or 3 gang - it is normally a manufacturing /inventory convenience - they are often used as one way)

[Paul Matthews]

Should be easy. Power off & disconnect all at the fitting. Light switch to on poition and use a meter to check which pair are shorted. Confirm bt switchig switch off and making sure no longer shorted.

P.

[Andy Wade]

The switch is obviously the cable identified as no. 3 in the original post. No. 1 is the incoming feed, no. 2 is a looped feed out.