Two-way light switch - Sorted, thank you all.

[Eric The Viking]

First-off, I'm trying to understand the fault condition.

I think I have got it.

The dining room is incorrectly wired.

It is behaving as if:

A: there is a THIRD switch somewhere, and the dining room switch is between that and the kitchen switch (see below).
B: at least two lives have been commoned to the kitchen switch, and the dining room switch is (incorrectly) inserted in one of them.

I'm on a tablet presently (at the breakfast table). Have to go sit at my PC to work in a few minutes, so I'll knock out a diagram then.

Whatever it actually is, your sparks is a pillock, and it is, most definitely, incorrectly wired up. It _might_ be a simple matter of altering the wiring to the dining room switch, or the switch itself might be the wrong type (and someone bodged it when they realised that).

Some single switchplates (really old or very cheap) only have two contacts - they are make or break and are not changeover. For twin switches, both need to be changeover (three terminals).

For three or more switches (usually only in stairwells), any switches in the middle are CROSSOVER (with four poles). They are specials: The switch always has two connections through it, but when operated they cross over:

State 1: A(in)--->A(out), B(in)--->B(out)

State 2: A(in)--->B(out), B(in)--->A(out)

The exact state of play in your house would be revealed by proper testing, but it's easy to guess at several mistakes that would give the symptoms you describe.

E.

PS: it's also possible that some real silly person has put the kitchen switch in the neutral (return) from the bulb. I didn't consider that initially, as you really have to be a total numpty to manage that one (and it is truly dangerous). I still cannot imagine how any sparks could say "that's correct" however it was actually achieved.

 

[Deejay]

Morning all

Anything could have gone wrong. In fact, more than one thing could be wrong. Chas and Eric have the solution in that you have to buzz out the wiring to find out what's happening.

First thing I would do is make sure that you have two way switches in both rooms.

My memory isn't what it used to be , so with anything like this I take pictures of the existing, put labels on each wire as I take them off and sketch where they came from on a bit of paper.

Once you have a switch out, test it for continuity from the Common terminal to both L1 and L2.

When you have all the wiring disconnected, buzz it out and you'll know which wires are in which cable and can re connect them correctly, assuming that you have enough conductors to do it properly.

Cheers

Dave

 

[Eric The Viking]

Here's a diagram or three:

Note: I deliberately haven't tried to show real-world wiring (yes, you NEED triple+earth (four core) cable!), as the way it looks behind the switches will depend on where the live comes in, and what, if any neutrals are passing through.

What I suspect happened is that during the last rewire, the owner belatedly asked for two switches for the dining room (you can see why - getting ready to come into the dining room with a full tray, forgot the light, etc.). The sparks explained that would mean digging out the cable to the dining room light switch (to replace it with triple+earth, or add an extra conductor), and that was considered unacceptable. So it was bodged - you could do wrong #1 by altering stuff in the joist (junction) boxes between the floors, but you'd still need three wires to the kitchen switch.

It also could have been done during a kitchen refit. Imagine a similar discussion.

If wrong circuit #1, it's annoying but not dangerous. If wrong #2 it's potentially nasty (unexpected live wiring).

The third-switch wrong variant is much the same, but with the third switch where the wire-to-wire joint is. The reason I mention it at all is that it would be nice to assume someone once did it properly, and the wrong switch was a later DIY bodge, but I fear that's not the case. I'll leave working out that switch logic, as an exercise to the reader!

 

[Sawdust Sam]

This is likely the issue, shame it’s american switches but the principle is the same, one of the switches is wired incorrectly.

https://m.youtube.com/watch?v=LozeRVU7YKU

 

[Deejay]

Afternoon Steve

PM sent

Cheers

Dave

 

[Eric The Viking]

This is likely the issue, shame it’s american switches but the principle is the same, one of the switches is wired incorrectly.

https://m.youtube.com/watch?v=LozeRVU7YKU

All very well, except his terminology is wrong (whichever side of the pond you live).

Both are two way switches (the toggle lever only has two positions), and single-pole, but one has a changeover function, the other is just single-pole make-break.

A "three way switch" actually has a centre position too, and isn't used in house wiring normally. You might see them for garage door openers "up--off--down", for example. In my former career it was also common for one side to be latching and the other to be momentary,

He's thinking of three-port valves in plumbing (or not thinking much at all), and those are really mis-named anyway.

The trouble with Steve's, er, trouble, is that it may be very hard to correctly wire the incorrect switch, if that switch uses plastered-in wiring that's only twin+earth. Unless there is a conduit of some sort (or it's studwork, which is unlikely on the ground floor), you'd have to channel the wall (and make good afterwards), and probably also lift several boards upstairs to finish the job.

The target audience for that video is a scary thought, too.

 

[Phil Pascoe]

I spoke to a friend, a motor electrics man one lunch time and he told me he'd spent the morning trying to find something on a car. I asked why he didn't have a manual for it and he said he had the full manual complete with diagrams - the diagrams showed him where in the scheme of things the part was (which he knew), but not where on the car it actually was. It's a little like a London underground map - you know whether a station is before or after another one, but not where it actually is.
Many wiring diagrams I've seen are a bit like this, they show individual wires - but not necessarily whether the wires are actually in the same cable.

One of the comments I caught briefly after that video was a guy saying he made a living correcting jobs done by people who followed videos like that.

 

[Woody2Shoes]

I've only speed-read this thread so apologies if I've missed it already.

One of the keys for my understanding of 2-way switching is that there are switches called "intermediate" switches - these are necessary in the intermediate positions between the first switch and the lamp. As described here:

https://socketstore.co.uk/articles/what ... te-switch/

I wonder if someone has swapped an intermediate switch for a "normal" one and maybe this is a source of the problem?

Cheers, W2S

 

[MikeG.]

I've only speed-read this thread so apologies if I've missed it already.

One of the keys for my understanding of 2-way switching is that there are switches called "intermediate" switches - these are necessary in the intermediate positions between the first switch and the lamp. As described here:

https://socketstore.co.uk/articles/what ... te-switch/

I wonder if someone has swapped an intermediate switch for a "normal" one and maybe this is a source of the problem?

Cheers, W2S

No, no. You're own link says that relates to 3 way switching, not two way. Two way switching doesn't involve intermediate switches.

Where there are obviously professional electricians giving their expertise in a thread on electrickery, the wise just watch from the sidelines and learn a bit. When even they get it wrong, people will realise I was right all along, and it is simple witchcraft.

 

[Sawdust Sam]

This is likely the issue, shame it’s american switches but the principle is the same, one of the switches is wired incorrectly.

https://m.youtube.com/watch?v=LozeRVU7YKU

All very well, except his terminology is wrong (whichever side of the pond you live).

Both are two way switches (the toggle lever only has two positions), and single-pole, but one has a changeover function, the other is just single-pole make-break.

A "three way switch" actually has a centre position too, and isn't used in house wiring normally. You might see them for garage door openers "up--off--down", for example. In my former career it was also common for one side to be latching and the other to be momentary,

He's thinking of three-port valves in plumbing (or not thinking much at all), and those are really mis-named anyway.

The trouble with Steve's, er, trouble, is that it may be very hard to correctly wire the incorrect switch, if that switch uses plastered-in wiring that's only twin+earth. Unless there is a conduit of some sort (or it's studwork, which is unlikely on the ground floor), you'd have to channel the wall (and make good afterwards), and probably also lift several boards upstairs to finish the job.

The target audience for that video is a scary thought, too.

Well you may be right but I believe it likely you are wrong. As I’ve said one of the switches is likely wired incorrectly rather than there being a missing wire.

We really need Steve to ping up some photos of each switch showing the terminals etc to bottom it out. Regardless of the terminology the video shows the issue clearly.

 

[Steve Maskery]

Thank you guys for all your input. But I've been out walking today (go a bit lost as the sun was going down, starting to panic but all good in the end, now bent double in pain and anguish), tomorrow I'm cooking and partying, NYD I'm away, probably, so I won't be in a position to do anything until Tuesday, but I will open it all up and share the horror.
S

 

[Eric The Viking]

... As I’ve said one of the switches is likely wired incorrectly rather than there being a missing wire.

Those things are not mutually exclusive.

I think it is the "wrong" switch in the dining room and it's wired up incorrectly (there is a missing wire between the switches).

The "wrong" diagrams I posted will replicate the symptoms Steve described. And the dining room being wired as if it's a single switch circuit makes complete sense as that's how it would have originally been done.

I'm not a betting man, but I think it's highly probable. But like many people who deal with electrickery I have learned there is no legislating for idiots. It's entirely possible that something even more bizarre is going on.

 

[Sawdust Sam]

... As I’ve said one of the switches is likely wired incorrectly rather than there being a missing wire.

Those things are not mutually exclusive.

I think it is the "wrong" switch in the dining room and it's wired up incorrectly (there is a missing wire between the switches).

The "wrong" diagrams I posted will replicate the symptoms Steve described. And the dining room being wired as if it's a single switch circuit makes complete sense as that's how it would have originally been done.

I'm not a betting man, but I think it's highly probable. But like many people who deal with electrickery I have learned there is no legislating for idiots. It's entirely possible that something even more bizarre is going on.

Your wrong diagrams may replicate the fault but I’ve never seen any wired as such in all my years as a sparky although I’ve not been in that game for many years now. In my experience the switches likely worked correctly once and someone has removed them at some stage in the past and then reconnected them incorrectly. Although not impossible I think it less likely there will be a missing wire between the switches, time will tell I guess.

To be clear there is no requirement to use a single 4 core cable for 2 way switching although it is an option, you can also use two core and earth ra5her than 3 core and earth. All your diagrams would normally be wired with T&E rather than 3C and E.

Your switch suggestion and the missing wire would replicate the issue but that would mean the install wasn’t completed by a sparky and has never worked, possible I suppose.

 

[CHJ]

Gents, none of the pontificating about wiring 'possibles' is going to help Steve sort his problem out.

As I've just posted on another thread and paraphrase here:-

With any process, piece of equipment, system or circuit that is not working as expected no amount of theory or expounding of pet theories is going to solve it. Until some accurate measurements of components ....*.... are done then it is unlikely to get sorted.

* in this case Steves actual wiring configuration and switch servicability.

 

[Steve Maskery]

Well I have eliminated one thing, the switch in the dining room is OK. I have continuity between COM and L1 in one position and between COM and L2 in the other.

However, there is something else inside the back-box that I don't understand. There is a black wire joined to a yellow wire with a choc-block, completely independent of the switch plate.

I haven't time today to do any more, I should have a cake in the oven by now and I haven't even been shopping yet.

 

[Eric The Viking]

Steve, this looks right (or at least sensible). In your picture, these should be:

• Red* (switch common): incoming live from the ceiling (either the rose or a joist box).
• Red & Blue: to the kitchen switch.
• Yellow: Final switched output up to the ceiling rose (from the kitchen switch), which becomes...
• ... Black*: final switched live to light fitting

* These two together are most probably a single twin+earth going up to the ceiling rose.
Old wiring colour conventions have been used, so it's not recent.

On the face of it, this all looks correct, or at least plausible, and the correct type of switch is being used, so Sam is right about this bit.

E.

 

[Sawdust Sam]

Well I have eliminated one thing, the switch in the dining room is OK. I have continuity between COM and L1 in one position and between COM and L2 in the other.

However, there is something else inside the back-box that I don't understand. There is a black wire joined to a yellow wire with a choc-block, completely independent of the switch plate.



I haven't time today to do any more, I should have a cake in the oven by now and I haven't even been shopping yet.

Ah progress, ETV post above describes how it’s wired but it is a strange way of doing it, what we need now is a similar pic of the switch connections in the kitchen switch before we can definitely resolve.

Here’s my best guess though based on a few assumptions that may or may not be right.

In your pic of the wiring in the switch you have an old T&E cable, one core is red and one black. This is old code cable and my guess is that this was the original switch and it was a simple single way switch with the live (red) coming to the switch common and the black being the switched live going back to the light fitting.

At a later date the owner decided a second switch in the kitchen would be useful and so the easier option is to run a three core and earth cable between the existing switch in the dining room and the new two way switch in the kitchen.

Now normal protocol when doing this wiring mod is to replace the original one way switch in the dining room with a two way switch (as you now have) and then connect the existing (old) red and black wire to L1 and L2 in the new two way dining room switch.

Now the new 3 core cable at the dining room switch is connected so that one core is connected to each of the switch terminals, common,L1 and L2. So in the dining room switch ignoring earning you would have two wires in each of L1 and L2 and a single wire in common. Normal protocol would have it that the cable in the common terminal is yellow.

Now the other end of the 3C &E cable in the new kitchen 3 way switch is simple connected one wire to each of the three switch terminals. The critical bit being that the same coloured wire must be connected to the common terminal in BOTH SWITCHES, ie the yellow core.

You could connect it as above and do away with the terminal block connecting the yellow and black wire at present and that’s what I would do. Here’s the wiring diagram to do as I suggest it should have been done ( note I’d use the yellow wire as common rather than red as shown below )



What I think you now have is the kitchen switch wired incorrectly and the yellow wire in the kitchen switch connected to L1 or L2 rather than the common terminal. If that’s the case then swapping the yellow and one of the other (red or blue) wires so yellow is in the common terminal will solve your switching problem.

 

[Eric The Viking]

In the kitchen:

• Yellow should go to common,
• Red and blue (crucially, from the same triple+earth to the dining room switch), to the other two switch terminals. It doesn't matter which way round.

As Sam says, I suspect red in the kitchen is connected to the common circuit instead. That's more usual use of the colours, and might explain why your recent sparks said it was OK - it looks like it is (in the kitchen).

When you put matters right, it doesn't matter if the switch is replaced upside down - this can be handy if the wires behind have been cut too short.

E.

PS: In case there is any really interesting wiring mistake still lurking, check everything is dead (isolated), with prods and a meter, between all switch terminals and earth, before starting to swap the wires over. If using a digital meter, there may be a few residual volts, but anything much above 10V would be cause for concern. Put the meter on a 250V AC range (or higher - it's 400V AC on my most commonly used meter).

PPS: Sam beat me to it whilst I was typing, and with a good diagram too!

PPPS: I'd also check the single choc-block connector in your picture of the dining room switch, too. The sparks put tape round it to no good purpose really, but the black wire has a bare bit - either stripped-back too much or because it's loose. that will be live when the light is on, but could just about touch a faceplate screw when it's all together, in which case it will trip something, probably.

 

[Steve Maskery]

The Yellow wire in sD is not connected to COM, it's connected to a choc-block to a black wire. In the switch itself, COM and L2 are Red, L1 is Blue.

 

[Eric The Viking]

Yellow goes to common in the KITCHEN. Leave the dining room alone, apart from checking that choc block.