I asked a builder to replace a plaster-board wall, and to do that he
disconnected the light switch. When he reconnected it, he seems to have
connected it up wrong. It was one of those switches for a hall light, so
that you can switch it on/off at two locations.

It ought to be simple enough to sort out, but the builder got into a panic
and seems to have reconnected all the wires at random, including opening the
ceiling rose and possibly fiddling with the wires there.

Of course, all the wires are buried in the walls/ceiling and none of them
are colour coded correctly any more. I think the original wiring may have
been done quite a long time ago.

I feel I ought to be able to sort this out myself, as I have a degree in
Physics.

Is there a normal layout for these switches, as it seems to me there could
be more than one way of wiring it to achieve the desired effect?

Is there a trouble-shooting guide?

I suppose I could start off by producing a chart of what happens when the
lights are switched on/off. In a nutshell, the light can be switched on at
either switch, but then it has to be switched off again at the same switch.

The builder put a new switch on the new wall. I have checked that it has a
common and two other contacts marked L1 and L2. This looks like the right
sort of switch to me.

Anyway, any help would be appreciated.

Thanks

Geoff

In article ,
GB wrote:
Is there a normal layout for these switches, as it seems to me there
could be more than one way of wiring it to achieve the desired effect?

This might help. Check the wiring on the other switch for colours.
Swapping L1&2 doesn't matter.



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

--
*The most wasted day of all is one in which we have not laughed.*

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
GB wrote:

Is there a normal layout for these switches, as it seems to me there
could be more than one way of wiring it to achieve the desired effect?


This might help. Check the wiring on the other switch for colours.
Swapping L1&2 doesn't matter.




That a very complicated diagram, even for a physicist. This is a bit
simpler, taking out all redundant lines:


L1 L1
0===========0
| |
Live ========0 0 ====================== Lamp
=========Neutral
\ /
0==========0
L2 L2
switch1 switch2


john2

GB wrote:

[...]
Is there a normal layout for these switches, as it seems to me there could
be more than one way of wiring it to achieve the desired effect?

There are two standard methods for wiring two-way switching. If your
wiring is reasonably modern, in flat twin-and-earth (and
triple-and-earth) cable, this reduces to one standard method. Dave
Plowman will be along shortly to post his usual diagram.

The builder put a new switch on the new wall. I have checked that it has a
common and two other contacts marked L1 and L2. This looks like the right
sort of switch to me.

Look at the other 2-way switch and ensure the the colours of the 3+E
(red, yellow, blue) cable are connected the same way at both switches.

One of the switches will have a second cable, this time only 2+E (red &
black, and the black should sport a red sleeve). Here the two wires
connect across the L1 and L2 terminals (either way round). Neither
should connect to the COMmon terminal.

All earths should have green/yellow sleeving and be connected to the
earth terminals in the back box (also to any earth terminal on the
switch itself, e.g. for a switch with a decorative metal front plate.

--
Andy

john2 wrote:

That a very complicated diagram, even for a physicist. This is a bit
simpler, taking out all redundant lines:


L1 L1
0===========0
| |
Live ========0 0 ====================== Lamp

\ /
0==========0
L2 L2
switch1 switch2


Yes, but that's the *other* standard method, only used if you're wiring
using singles in conduit. Dave's diagram is far more likely to be what
the OP actually needs.

--
Andy

Is there a normal layout for these switches, as it seems to me there could
be more than one way of wiring it to achieve the desired effect?

There are indeed a number of ways of wiring these things. However, the best
and most common method was shown by Dave Plowman. John2 produced a different
method which has significant disadvantages, but is still regularly found,
especially in older installations.

It may help us to indentify which method if you explain what cables are
present at each point. Ignore any earth conductors. Only count proper
coloured and insulated conductors. Please tell us how many 2 or 3 conductor
cables are at each switch and the ceiling rose.

Christian.

In article ,
john2 wrote:
That a very complicated diagram, even for a physicist. This is a bit
simpler, taking out all redundant lines:


L1 L1
0===========0
| |
Live ========0 0 ====================== Lamp
=========Neutral
\ /
0==========0
L2 L2
switch1 switch2

Your way involves jointing a cable somewhere in most installations. Mine
doesn't.

--
*I don't suffer from insanity; I enjoy every minute of it.

Dave Plowman London SW
To e-mail, change noise into sound.

Thanks all for the help. I'm not currently staying at the house, so I will
need to go over to check it out. I'll report back later.

Yes, but that's the *other* standard method, only used if you're wiring
using singles in conduit. Dave's diagram is far more likely to be what
the OP actually needs.

I was trying to draw a basic circuit diagram to get the point across,
rather than a physical wiring diagram which is a lot more complicated.
Ah well....


john2

In article ,
john2 wrote:
Yes, but that's the *other* standard method, only used if you're
wiring using singles in conduit. Dave's diagram is far more likely
to be what the OP actually needs.

I was trying to draw a basic circuit diagram to get the point across,
rather than a physical wiring diagram which is a lot more complicated.
Ah well....

Most recent wiring uses the switch pair from a ceiling rose method, so
that both these wires arrive at the one switch on a two way circuit. Your
diagram suggests you need to joint one wire to feed the two way circuit
between the switches if this is the case. If someone doesn't understand
how a two way circuit works this only really adds confusion as they're
likely to do just that.

--
*The early bird gets the worm, but the second mouse gets the cheese *

Dave Plowman London SW
To e-mail, change noise into sound.

I have now checked the wiring at both switches and the ceiling rose

Ceiling rose:

Two black wires come in, one with a red sleeve - connected to opposite poles
of the bulb holder.

Also, two red wires come in, connected together in a spare terminal, not
connected to anything else.


Switch 1:

Red to common
Blue to L1
Black to L2


Switch 2:

2 red wires connected to common
Black to L1
Different black wire+ blue wire connected to L2

I am afraid that without testing it all out with a continuity tester, I am
not at all clear what is connected to what.

In article ,
GB wrote:
Ceiling rose:

Two black wires come in, one with a red sleeve - connected to opposite poles
of the bulb holder.

Also, two red wires come in, connected together in a spare terminal, not
connected to anything else.


Switch 1:

Red to common
Blue to L1
Black to L2


Switch 2:

2 red wires connected to common
Black to L1
Different black wire+ blue wire connected to L2

I am afraid that without testing it all out with a continuity tester, I
am not at all clear what is connected to what.

You can't blow a fuse by experimenting, so I'd try moving one of the red
wires in SW2 to LI. If that doesn't work, try moving the other one.

--
*If I throw a stick, will you leave?

Dave Plowman London SW
To e-mail, change noise into sound.