Light switch wiring

[Evan Brown]

I'm doing up a house that I own at the moment after a tenant left it in a less than perfect condition at the conclusion of a long-term let.

He's managed to rip a light switch clean off the wall. The switch is for two wall up-lighters and the original wiring was a mess when I found it.

Currently I have three two-core cables at the switch - all are colour coded blue and brown for neutral and live which I think is non- standard. Anyway, two of the cables go to the first light (the terminal block behind the light has two live wires and two neutral wires going into it.) The second (furthest away) light only has one live and one neutral cable going to it.

I bought a new light switch. It's the only switch for the lights and the terminals on the switch are marked L1, L2 and Common.

I think that I need to put the feed live (from the mains) into the Common terminal. I think I then put the live wires from the other two cables into the L1 terminal on the switch and connect the neutral wires together in a terminal block so that they are unbroken from the mains. Is this correct? How do I know which live cable should go to Common as there is no black sheathed cable - only three brown cables to choose from?

I know that I should call an electrician etc. but the nearest sparky is 100 miles away and this should really be a simple job. Any advice on what to do would be much appreciated.

[jgharston]

That's the new standard, though I keep having to stop myself calling them blue and red. ;)

What I would do - as an experienced electrician, and I'm not recommending you do this unless you know you can do it safely and competently - is ensure the wires are all electrically seperated (eg by connecting them to seperate terminals of a 6-way connector block), turn the power on, and then test between brown & blue on each pair to find the incoming feed. Had to do that just a couple of days ago to find which cables coming into two pairs of sockets were the legs of the ring back to the CU.

JGH

[Mr Pounder]

He should pay for a electrician. All like take and no like pay. I wonder if the gentleman is aware that may require fire protection in his building?

>

[Evan Brown]

Ah, an archetypal Usenet moron replies. I take it you've lined up all your paper clips and alphebetised your CD collection already and have now run out of things to do. Why not go for a drive so that you can give other road users the benefit of your unmatched experience and skill through the illegal use of your horn?

There are no tradesmen within 100 miles of my property and last week I paid a locksmith =A3327 just to replace two cylinder locks in a set of French windows. =A3200 of that charge was for travel.

The wiring in the house has been in for fifteen years and was a self- install job from the start - I know the guy who used to live in the house and who did the work himself.

I'm not interested in your opinion unless it relates directly to the substance of the question that I asked and I take any advice given entirely at my own risk.

[Andy Wade]

Brown & blue ('harmonised colours') have been allowed since 2004 and mandatory since 2006. The cables are, I hope, actually 3-core with the earths sleeved green/yellow and connected together in the switch's back box.

Not quite, but it does sound as if you have the 'switch feed' type of wiring. To help confirm so, check the following:

- this is a one-gang, one-way switch (one switch for the two lights, and no other switch(es) control the same lights);

- at the light with two cables they are simply connected in parallel, brown to brown and blue to blue - this will be an incoming switched feed to the first light (from the switch) and an outgoing feed to the second light;

- at the switch, the three blues are, or were, connected together with an insulated terminal.

Assuming the above is the case the three cables at the switch will be an incoming mains feed (brown line, blue neutral), an outgoing ditto to another switch, and a switched feed for the lights.

You need to find which cable is the one that feeds the lights. Isolate the circuit and turn off all other lights on it. Ensure that at least one of the lights in question has an intact filament 'bulb' in it, not a CFL. A continuity check with a multimeter on a resistance range will then find the desired cable - you'll read the cold resistance of the lamp(s). (Confirm by removing lamps, if necessary). The other two cables will read open-circuit (or possibly a higher resistance if there's a shaver transformer or similar on the circuit).

The connections required are then:

- 2 lines, incoming and outgoing feeds, to one side of the switch (COM or L1);

- 1 line, identified as switched feed to lights in question, to other side of switch (L1 or COM);

- 3 neutrals, connect together with a terminal block, ensure no bare copper is showing, i.e. no risk of neutral-earth (or any other) shorts.

Restore power and test. If the switch works upside-down, swap L1 connection(s) to L2.

HTH

[ARWadsworth]

Odd colours for a 15 year old cable. Is it twin and earth cable or flex?

What test equipment do you have (multimeter etc)?

Cheers

[John Rumm]

Two core and earth or just two core?

That does not seem quite right...

I could understand one feed cable into the switch and two switched outputs - one to each light. However you would only have one cable terminating at each light.

I could also understand one into the switch and one out, with the out feeding the first light, and that having a second cable to feed the second. That would match what you see at the lights but not the switch.

You seem to have both - which suggests there more going on that at first meets the eye.

It could be that they have wired the switch in the "loop in" style you would normally use at a ceiling rose. Then one cable will be the mains in, the second will be mains out to the next light on the circuit, and the third would be the switched feed to the first wall light. The first light having an additional cable to feed the next one.

Possibly, but given my comments above probably not.

Not sure why you would expect there it be a black cable (assuming this is all wired with new colours)?

Turn the power off to the circuit and disconnect all the wires. Take the bulbs out of the fittings, make sure if they have any additional switches in the fittings themselves they are turned on. Using a multimeter on an ohms range measure the resistance between the two pins on the bulb holder. You should see open circuit. Now short the L&N of one of your cables together. If that is the connection to the light, you will see low ohms when you repeat the resistance measurement at the bulb holder. If not unshort that pair and try the next. Repeat until you find the feed to the lamp. At this point I would also check the resistance at the second lamp location. Chances are you will see the short there - this would suggest that the first lamp feeds the second. If its not also shorted, then see if this lamp is fed from one of the other cables by the same process as above.

Assuming you ultimately find its loop in wires (one in, one out, one switched out). Then you would have all neutrals joined in a separate terminal. The Live in and Live out joined at COM, and the switched live out in L1 (you could of course reverse the function of L1 and COM or use L2 instead of L1 and it would make no practical difference)

[John Rumm]

Wrong group old bean, uk.i_am_helpless.pay_to_get_a_man_in is thatway ->

[Skipweasel]

Er - this is usenet - you'll get opinions of all shapes and flavours, many unrelated to the original question and some tangential to the point of obscurity. Unless you like being very frustrated, I'd get used to it, if I were you.

As to the wiring...your best bet is to work it out from first principles on a bit of paper. The fundamentals are that the flow (yeah, I know it's AC) goes from the circuit breaker through the switch and the bulb to the neutral. Sometimes the switch is before the bulb.

Since the chances of any self-installed wiring following a set colour scheme are slim, it really is going to be down to chasing wires through and making a few educated guesses which you then test to see which was right.

[jgharston]

Yes, re-reading there's something odd there. "I have three two-core cables at the switch" "Two of the cables go to the first light"

I think I subconciosly edited that to "two of the cables go to the lights, ie:

SUPPLY / BRN -------o/ o--+-BRN----------------* BLU ---------@--+-|-BLU----------------* LIGHT | | | +-BRN----------------* +---BLU----------------* LIGHT

which my testing method would identify the supply, the two others are the lights. Similar to:

However...

That suggests this:

SUPPLY / BRN ---+-o/ o----BRN--------------+--* BLU -+-|---@------BLU------------+-|--* LIGHT | | | | | +--BRN----> TO NEXT | +--------------* +----BLU----> CIRCUIT +----------------* LIGHT

ie, this:

Which needs John's more involved testing to identify the switched light feed and the loop-out feed to the next circuit.

JGH

[alan]

Hang on - this is the pc riddled heath n safety UK Ltd! Is he even allowed to look at the cables without risking a prison sentence!

[Tabby]

Something is wrong with this picture. At an absolute minimum, one of the cables to the switch should have an earth wire.

Imho its necessary that you find out what's going on with the cables before connecting them up. If you don't make the effort to determine this,

- you're connecting up a circuit that you know is non-compliant with wiring regulations

- a switch ripped of the wall is a good hint that when wired up it didnt work, or possibly worse

What I would do: I'd expose the light fitting wiring and use a multimeter to trace the wires to/from the lights. I'd then use the multimeter to find out what's going on with the other cable/flex or 2. Ideally you should then replace the feed with 3 core and wire it all up.

Switches with common, L1 and L2 work as an ordinary on off switch when you use common & L1. It dosent matter which terminal is which.

You need a multimeter, assuming you can do this without endangering anyone.

[BartC]

Why?

A HMO might require fire-doors and such but this sounds an ordinary tenanted property.

[Mike Humphrey]

That can't be right - the brown/blue colour code for fixed wiring came in between 2004 and 2006 (see

so this wiring can't be more than 7 years old.

Mike

[The Other Mike]

Unless this 'fixed' wiring is flex...