Hello all, right I have a problem with two way switches. This is the situation, downstairs I have a two gang two way switch (well I think its two way....) controlling the downstairs light and (With a sep. feed) the upstairs light.
So the wires downstairs are: one 2C+E switch cable, and two 3C+E linking cables Upstairs is the same the two linking cables and the one switch cable
The switches have two sets of terminals labelled L1, L2, and L3 (which I presume is COM)
Ok still with us... So downstairs the switch is wired as follows: Switch Cable: Red: L1 Switched Live: L2
So there's two sets of L1, L2, and L3 on each switching plate which each of which has one of the linking cables attached, and one also having the switching cable attached. The other light switch is wired the same with obviously the other linking cable being attached to the other switch cable.
Lights are wired using the loop in system and they are all correct I have checked that I am using the correct linking cable for each and that I have not swapped them over by mistake.
So what's wrong any one got any ideas, the only thing I can think of is that the cables got damaged but I cant see that both have been damaged. Thanks for any help J
Well, you can check the circuit by simply connecting the two wires in the switch pair together - if the light then works, the fault must be in the two way circuit. Anyway, here's the pukka circuit.
L1 L1 0===========0 0===========0============= Line | \ / | C 0================================O C \ / \ / 0===========0 0===========0============= Switch return L2 Optional L2 Intermediate
Well, since you talked about a loop in system, I assumed you'd know which these were. They are the two wires, in one cable, which go from the ceiling rose to the switch - regardless of whether a one or two way switched circuit. A line - usually red, and the switch return - usually black.
Hmm. At this point consult a qualified electrician sounds like the best advice.
As a young person of my acquaintance would have it: "unlucky".
If you can't follow that diagram, you almost certainly shouldn't be touching the electrickle wiring in your house.
On the vaguest possibility that the way Dave's drawn it somehow foxes you, but you grasp the basic idea of current flow... The "L1, C, L2" bit at the lefthand end indicate one of the two two-way switches - surely you recognise those as the labels of the terminals in such a switch, no? Same for the other group towards the right of "L1, C, L2". The little \ and / characters at the LH and RH switches show the position of the switch contacts. In a 2-way switch, the C ("Common") terminal connects to either the L1 or the L2 terminal, changing when the switch is operated.
So - ignoring for now the "optional intermediate" - the diagram shows that the "Line", "permanent live", "input" or whatever you want to call the wire which feeds the incoming current, runs to the L1 connector of one 2-way switch, and also on to the L1 connector of the other one. The "switch return", "switched live", "output", or whatever you want to call the wire which supplies the switched current to the load, similarly comes from the L2 connectors of both switches. It should be obvious from the way 2-way switches work that these 2 wires alone won't ever make the "switch return" live - the L1 and L2 terminals are never connected by the operation of the switch alone. The flow is completed by the third wire which joins the two "C" terminals. When the switches are both in the "L2" position, as shown on Dave's diagram, the light is off - neither switch makes any connection to the "line"/"permanent live" wire. If either of them is operated, the light is on: the one that's operated joins its L1, where the incoming live is, to its C terminal; current passes along the C-to-C wire to the other C terminal; and through the switch which is still in the L2 position to the "switch return" wire and on to the load. If the second switch is then moved to the L1 position, the light is off again - now the "switch return" wire has no connection to the incoming live, which is ready-and-waiting at the L1 and C terminals of both switches, but has nowhere to go. "Clearly", then, flipping either switch - but not both - reconnects the switch-return to the live C terminal of the just-operated switch: ooh, light on again.
The "intermediate" switch - which you can have any number of, to give switching at more than two points - swaps over the "perm live" and "switched live" segments, which has the effect of "reversing" whether the two end switches need to be both-the-same or each-different in order for current to flow to the load.
If you can't see what relevance this has to your particular setup, give up this time and get someone in. If you want to figure it out for another time, do some playing around either on paper, or if you prefer hands-on, a battery or suitable low-voltage power supply, bulb, a couple of two-way switches or some crocodile clips simulating same, and a few lengths of wire. (It's NOT a good idea to practice circuit understanding with 240V mains.)
What actually happens with the light is if its turned on upstairs (or downstairs) I am unable to turn it off on the other switch. I have tried one switch at a time with each one of the two linking cables to make sure that the cable isn't damaged, the switches also work as one way switches without the linking cable, any ideas where next?
Sorry I should have re read my OP as I never actually mentioned the problem so wasn't too sure where you were heading with this, as I thought I mentioned the problem but clearly didn't.
Thanks for the detailed post Stefek, I can follow what goes on in a two way switch (The days of electronics at school) I just cant work out why mines not working as a two way switch (See post below)
So in "electronics" speak, you've implemented an inclusive-OR - on when either sw passes current to the sw-return wire - rather than the exclusive-OR you wanted (sws to be in different positions for current to flow). See if you can think through what pattern of (mis)wiring would account for that. One way (and by no means the only) is if you'd swapped over the roles of the top and middle wires on Dave's diagram, i.e. wired perm-live to both C terminals and taken the sw-return from both L2s (or, indeed, both L1s). Then operating either switch completes a circuit from perm-L to switched-L, with the other having no effect.
Think it through logically, follow your hyptothesis with a bit of tracing (easier if you have a meter!), and you'll get there. Without a meter, you may *assume* you know where cables appear and disappear, but there's always the bugger factor of a hidden junction box or similar mid-circuit Surprise!
The likely reason is that if the switches are wired L1 to L1, L2 to L2 etc as in my diagram then you've wired the switch pair across the common and one of the 'L' s. I'm not sure which is common with an L 123 layout - but it should be obvious by looking at the switch - the common will be the single terminal opposite the two Ls.
Thinks
If a two gang, you're not assuming one switch has all the terminals in a line? This is the usual layout of a two gang two way switch.
Have you proved that L3 on your switch is in fact the COM terminal? Might be worth buzing out the switch with a multimeter to be sure.
Imagine what you woulf get if the terminal allocation was like below:
===============*
============*=============== Live \ \ ===============*============ Sw Return
With your live connected to what is in fact the COM terminal rather than L1. Once the switch is closed at that end nothing you cn do with the other one will make any difference.
Thanks for all the help, I finally cracked it, thanks to someone's reply that COM is the terminal on its own, so where there's L1, L2, L3 labelling L1 is infact COM why not use come I don't know.
On Wed, 29 Dec 2004 18:27:17 -0000, "John Borman" strung together this:
Exactly what my first thought was, easy when you know how!
Well, if it was called L1 then it would be L1. If it had never been called COM then you would never know, IYSWIM. When you work with these things every day it's not a problem.
You need to get yourself a DVM. Prices start at well under a fiver. That would have shown which terminal does what in seconds. Never assume anything with terminal numbering as there's no standard.
A changeover switch like this should really be labelled Com, NO (normally open) and NC (normally closed).
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