what might be wrong with this wiring?

What might be wrong with mains wiring that behaves as follows, connecting two lamps in parallel to two switches, S1 and S2.
When S1 is switched one way, everything works fine: S2 toggles the lamps on and off.
When S1 is switched the other way, the lamps are always on.
Now swap L1 and L2 inside S2, and we get
When S2 is switched one way: everything works fine: S1 toggles the lamps on and off.
When S2 switched the other way: lamps always on.
Thanks for any help with this.
There is no fault in either switch.
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On 8/21/2017 9:23 PM, Harold Davis wrote:

Someone who likes puzzles will probably come along in a minute and unravel this for you.
But personally, I would tackle it by disconnecting all the wires at the two roses and splay them out so that nothing is touching. On a good day, I might mark up the original connections, but then again I might not.
Then I would use a volt stick (or neon screwdriver or DVM) to locate the live incomer. You need the mains on for that. Mark that one with red tape, then turn the circuit off for everything else.
Figure out which rose wires go to which switches using a DVM in "ohms" mode.
There may be a pair of spare red and black wires which don't seem to be part of the circuit. They will be the ones which take unswitched live and neutral on to the next rose.
If, when you disconnect these roses, all your other lights still work then they are not feeding any other lights.
If you find some of the black wires have a red sleeve on them, God has been kind to you. The electrician is showing you where the switched lives are. (When I say red and black, I am using that term to include brown and blue, if the wiring is sufficiently recent).
With any luck you might find that the two way part has been wired up with three core plus earth cable, which also makes the diagnosis much easier.
Oh, and draw a diagram of everything as you begin to sort it out, you will get something wrong if you don't.
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My habit now is to take digital photos of stuff as I dismantle it, just in case.
--
Graeme

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And next time you won't remember it of course! I had a lot of head scratching when I put on a timer on off switch in place of one of the 2 way switches once. I mean what could possibly go wrong I thought.. Ahem. Brian
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Your description of the effects applies irrespective of whether L1 abd L2 in S2 are swapped or not. Two single pole switches in parallel behave in the way you describe. When one switch is open the other one does the toggling. When one switch is closed the lamps are on and the other switch has no effect.
--
Dave W



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The switches are in series; it's the lamps that are in parallel.
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On 21/08/2017 23:02, Harold Davis wrote:

The switches can't be in series, otherwise opening either would always turn the lamp off - and that does not match your description.
Here is how they should be wired:
http://wiki.diyfaq.org.uk/index.php/2_Way_Switching
--
Cheers,

John.
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abd

Sure. I mean the switches should be in series. I left some of the old wiring in place and am trying to work out is wrong. I tested all cables coming from both switches. I thought I did it as shown on that page. I did this before in a garage without a problem. Something strange is going on with those old wires.
Harry
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On Tuesday, 22 August 2017 00:42:41 UTC+1, Harold Davis wrote:

No, the switches should not be in series!
NT
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snipped-for-privacy@gmail.com wrote in

What's wrong with how they're done in this diagram?
<
http://i.imgur.com/B8cL27A.gif

Harry
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On Tuesday, 22 August 2017 02:28:36 UTC+1, Harold Davis wrote:

that's correct.
NT
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snipped-for-privacy@gmail.com wrote in <snip>

I would say those two switches are in series. Am I mistaken to use the word "series" in this context?
Harry
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On 22/08/2017 11:34, Harold Davis wrote:

In that particular case neither term is totally correct since you in effect have two sets[1] of series switches wired in parallel
[1] since they are single pole double throw aka "changeover" / "two way" switches.
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John.
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Thanks :)
I was thinking in the cruder terms of
(cables)..(switchbox)..(cables)..(switchbox)...(cables)
Could we say the switchboxes are series?
Harry
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>> In that particular case neither term is totally correct since you in

I mean "in series". Damned typo!
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On 22/08/2017 14:30, Harold Davis wrote:

It would seem that one of the conductors between S1 and S2 is connected to a 'live' feed from somewhere else which would give you the condition you describe.
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On 22/08/2017 14:30, Harold Davis wrote:

In the grand scheme of things it does not really matter what you call them, so long as they work!
ISTM you need to go back to basics and work out what wires you have going where, and then build things up logically when you know what you are starting with.
Do you have a multimeter so that you can test which wires are live and also which ones are connected to each other?
The first step is finding the power feed to the lamps (normally twin an earth). Then identifying the switch drop wires bwtween the roses and the switches (again normally T&E even on two way switched systems), and finally the link cables between the switches (normally 3&E).
(you can test whether two possibly connected cable ends are in reality connected if you twist the wires together at one end, and then measure the resistance between them at the other)
Needless to say (and apologies for stating the obvious), but do all the investigations and test connecting with the power to *all* circuits turned off until you have made sure you know what is being powered from where. If you accidentally short something, its much better to be operating the MCB in the CU than fiddling about with multimeter probes in the back of a switch or rose.
--
Cheers,

John.
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On 22/08/2017 02:24, Harold Davis wrote:

Nothing so its a safe bet that they are not wired like that.
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OK. I have already tested what I thought might be an offending switch by putting a new switch in its place, but that didn't affect what is going wrong. There is probably something strange happening in a small section of old wiring I left (having fully tested it before doing anything!), which comprises two lengths of 3-core coming from that switch ( and {common, unconnected, earth}). The second possibility is that there is something wrong with the similar wiring I left (again fully testing it) from the other switch. Those are the only sections I left in place other than the mains feed. The third possibility is that I failed to follow my own plan properly, so I will check everything I've done.
First I will disconnect the cabling to the first switch and replace it with a switch and test cabling. Hopefully that will solve the problem and I can then put the new cabling in place. If that doesn't work, I will recheck everything I've done. If I haven't made an error, then the problem can only possibly be the cabling to the other switch (that switch is new and works fine, and again I tested the cabling fully), which will be a nuisance to replace but it will have to be done.
The circuitry is a little more complicated than I showed. The two lights are on the ceiling of the garage and there is also an outside light in parallel, controlled by its own switch. That didn't work before, but now I have done what I've done it works fine! So the full circuit I want is this: <
http://i.imgur.com/bQ7jqnL.gif .
Harry
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Wastes cable if using TW&E.
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*If at first you don't succeed, redefine success.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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