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
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.
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
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 £327 just to replace two cylinder locks in a set of
French windows. £200 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.
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
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.
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
- 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
- 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.
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)
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:
BRN -------o/ o--+-BRN----------------*
BLU ---------@--+-|-BLU----------------* LIGHT
which my testing method would identify the supply, the two others
are the lights. Similar to:
That suggests this:
BRN ---+-o/ o----BRN--------------+--*
BLU -+-|---@------BLU------------+-|--* LIGHT
| | | |
| +--BRN----> TO NEXT | +--------------*
+----BLU----> CIRCUIT +----------------* LIGHT
Which needs John's more involved testing to identify the
switched light feed and the loop-out feed to the next
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
- you're connecting up a circuit that you know is non-compliant with
- 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
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
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