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

[Steve Maskery]

Evening chaps.
My dining room light is switched from two locations. I have a switch in the dining room (sD) and another in the kitchen (sK)

sK works as it should, that is to say if the light is off, it switches it on, and if the light is on it switches it off.

However. sD only works if sK is in just one of its two positions. In the other sK position, sD does nothing.

Now I do understand how two-way switching works, I used to teach o-level physics, but I don't understand this. Is it wired incorrectly somehow or is it a dodgy switch, and if so, how do I identify which one? sK is a triple-switch plate, two of which are 2-way. The other 2-way circuit works as it should.

BTW, this hasn't suddenly started happening, it's been like it since I moved in, I've just never done anything about it.

All help gratefully received.

 

[MikeG.]

It's witch-craft, Steve. Drown your cat and tie it's body to your chimney. You'll be fine.

 

[Brandlin]

it is wired incorrectly.

You should have 2 way switching in both switches and 4 core cable running between the two switches (traditionally red, black, blue and yellow)

My initial bet is that you dont have 4 core cable running between the switches. This would give you the situation you describe above.

Assuming you have everything cabled as required, it sounds as though you either have a poor connection in Sk meaning that one of the Sk switch positions is not creating a continuous contact.

As always if you don't know what you are doing, then don't. etc.

 

[CHJ]

Think the only sound way to sort it is to isolate the circuits from the supply and continuity check the wiring to determine if it's switch cross-over wiring, links to-from ceiling rose or faulty connection.

So many ways circuit may have been envisaged by someone in the properties' past history when older wiring systems were the norm.

I had similar problems with a 3 Way switched lighting circuit on our stairs that had been permed by someone with another 2 way circuit in the co-located triple switch units in hallway housing yet another two way circuit.
Any one of 5 switches would actuate or switch off a light in a totally unrelated location.

 

[user 4112]

I’m not a domestic sparks but have been involved in wiggly amps all my working life. Brandlin's 4 core cable sounds a little over kill. Have a look at this for a simpler wiring diagram.

https://www.google.co.uk/search?q=2...AUIESgB&biw=725&bih=518#imgrc=4B7d-6OvjdcSnM:

My current house had one light operated from 3 switches, clearly the previous occupant hadn't heard of intermediate switches. What fun I had sorting that out.

 

[Phil Pascoe]

You need an earth and three others for two way switching in normal household wiring - surely it can be done other ways, but some of them seem more complicated than just starting with four core.

 

[Steve Maskery]

Thanks chaps. I would expect 4-core, that makes sense to me. I'll have a peek inside in daylight.

Mind you, after what I've found today in another, afterthought, part of the house (think 1970s Batik), I'm not sure I want to know.

Thank you all.

 

[Brandlin]

I’m not a domestic sparks but have been involved in wiggly amps all my working life. Brandlin's 4 core cable sounds a little over kill. Have a look at this for a simpler wiring diagram.

https://www.google.co.uk/search?q=2...AUIESgB&biw=725&bih=518#imgrc=4B7d-6OvjdcSnM:

No, its NOT overkill. 4 core cable (sometimes called three core+ earth) is the only way to make 2 way switching work!
Every one of the diagrams you link to shows the use of 4 core cable!
If you really dont know what you are talking about then its probably best NOT to advise others!

Steve Maskery - Your switching should be arranged as shown in the diagram below.

The fault you are describing is because ... Imagine connection 1-1 in the diagram is missing. when the left hand switch is in the 1 position, it doesn't matter which position the right switch is in there is no current able to flow from the left switch to the right. Now put the left switch in the 2 position and the current flows to the right hand switch. If the right hand switch is in position 1 then the circuit is broken and the light is off. If the right hand switch is then put into position 2 the light comes on.

Its simply been incorrectly wired using standard three core cable. You can tell if this is the case, as each of the switches should be of the "2 way" type, and should have FIVE terminals labelled L1, L2, (COM)mon, (N)eutral and (E)arth. There are two ways of wiring the switches depending on whether the lighting ring is cabled as "loop-in" or "direct". In either case all of the terminals should have wire connected to them. But whichever way it is meant to be cabled - If you have an empty terminal then this is whats wrong!

It is possible to get this fault also because of a discontinuity in the cable. You may have 3 core plus earth cable running and correctly wired, but a faulty switch, bad connection at the brass terminal or a break or discontinuity in the manufactured cable. All of these are rarer, but i have seen them all over time. Only last month when wiring up my router table I found a 4m length of flex with a discontinuity in the brown wire. it can sometimes take you ages to find that!


form your description its clear you know something of wiring but i would advise if you aren't absolutely sure what you are doing.... then find someone who is.

 

[Steve Maskery]

I did actually ask (and paid) a "proper" sparky to check this for me and he said everything was alright. It was when I wasn'r very well and I can't actually remember the details, but it doesn't work now any better than it did then. I'll see what I can determine.

 

[CHJ]

No, its NOT overkill. 4 core cable (sometimes called three core+ earth) is the only way to make 2 way switching work!
Every one of the diagrams you link to shows the use of 4 core cable!
If you really dont know what you are talking about then its probably best NOT to advise others!

.

Glad you are not the sparky quoting me to fix anything in my property, more than half the lighting feeds and switching wiring is twin & earth 3/029 and separate single core 3/029, (Red & Black).


Steve has the house been rewired since metrication of wiring? Your house is considerably older than mine so unless it has been rewired since we changed to metric wiring there is a very good chance it has no 4 core wiring.

 

[Phil Pascoe]

... more than half the lighting feeds and switching wiring is twin & earth 3/029 and separate single core 3/029, (Red & Black) ...

So from the point of view of switching you have three core and earth. Why wouldn't it have three and earth with modern wiring?

 

[harvestbarn]

Often a 3 core + earth is wired between the two switches , a twin + earth is taken to one switch bringing a live and taking back the switched live, both conductors should be marked as live. See https://www.google.co.uk/search?hl=en-G ... 4581124983
The neutral is looped into the ceiling rose. Hope this helps.

 

[Brandlin]

No, its NOT overkill. 4 core cable (sometimes called three core+ earth) is the only way to make 2 way switching work!
Every one of the diagrams you link to shows the use of 4 core cable!
If you really dont know what you are talking about then its probably best NOT to advise others!

.

Glad you are not the sparky quoting me to fix anything in my property, more than half the lighting feeds and switching wiring is twin & earth 3/029 and separate single core 3/029, (Red & Black).

To enable two independent switches to operate the same fixture REQUIRES two live cores, a neutral and an earth.

More than half of the lighting feeds and switching is twin and earth because it is not utilising two switches on the same fixture.

Now you may encapsulate 3 of those cores in one sheath and use the core of a separate cable to run in parallel. But you are still using 4 cores. PERIOD.

Feel free to raw up your version of an arrangement with less than four cores.... would love to see it.

 

[CHJ]

... more than half the lighting feeds and switching wiring is twin & earth 3/029 and separate single core 3/029, (Red & Black) ...

So from the point of view of switching you have three core and earth. Why wouldn't it have three and earth with modern wiring?

No reason at all, but don't assume that when folks have switching or wiring faults in older properties that the property is wired with modern wiring to the IEE (IET) wiring regulations (BS 7671)17th edition or its recommendations.

Just try fitting some brands of modern replacement sockets onto Power ring mains that are wired in 7/029 as another interesting exercise.

 

[CHJ]

No, its NOT overkill. 4 core cable (sometimes called three core+ earth) is the only way to make 2 way switching work!
Every one of the diagrams you link to shows the use of 4 core cable!
If you really dont know what you are talking about then its probably best NOT to advise others!

.

Glad you are not the sparky quoting me to fix anything in my property, more than half the lighting feeds and switching wiring is twin & earth 3/029 and separate single core 3/029, (Red & Black).

To enable two independent switches to operate the same fixture REQUIRES two live cores, a neutral and an earth.

More than half of the lighting feeds and switching is twin and earth because it is not utilising two switches on the same fixture.

Now you may encapsulate 3 of those cores in one sheath and use the core of a separate cable to run in parallel. But you are still using 4 cores. PERIOD.

Feel free to raw up your version of an arrangement with less than four cores.... would love to see it.

No one is disputing the need for the number of cores, just pointing out that Steve may not have 3 core and earth (4core cable) in his switch circuit)

 

[Lons]

switches should be of the "2 way" type, and should have FIVE terminals labelled L1, L2, (COM)mon, (N)eutral and (E)arth.

Strange ! None of the switches I've encountered in domestic lighting have ever had a Neutral terminal as N is usually supplied to the lamp fitting from the ring circuit

 

[Brandlin]

switches should be of the "2 way" type, and should have FIVE terminals labelled L1, L2, (COM)mon, (N)eutral and (E)arth.

Strange ! None of the switches I've encountered in domestic lighting have ever had a Neutral terminal as N is usually supplied to the lamp fitting from the ring circuit

Then you have only ever worked on loop-in wiring ring circuits which tends to be the modern preference. Older properties often have power supplied to the switch and then on to the lamp fixture.

Its also the case that in switches in this arrangement the neutral connection has been made by chop-block, rather than a moulded in terminal. So i agree my use of the term "five terminals" can be misleading - but certainly you need to make 5 connections in that arrangement.

 

[Lons]

Then you have only ever worked on loop-in wiring ring circuits which tends to be the modern preference. Older properties often have power supplied to the switch and then on to the lamp fixture.

Its also the case that in switches in this arrangement the neutral connection has been made by chop-block, rather than a moulded in terminal. So i agree my use of the term "five terminals" can be misleading - but certainly you need to make 5 connections in that arrangement.

You have absolutely no idea what I've worked on during my business as a builder! That included some VERY old properties. What qualifications do you have to make statements in such a commanding manner, especially when they are misleading and inaccurate?

switches should be of the "2 way" type, and should have FIVE terminals

Correct, Your statement was not only misleading but wrong! If you need to replace a switch then it will be of modern type and definitely will not have 5 terminals.

Correct that the N line may well be carried through inside the switch box but will not be connected to the switch plate but for a long time the neutral feed has been supplied to the lamp holder without coming anywhere near the switches. However that is not what you stated.

 

[CHJ]

My property (built circa 1962) has a mixture of live feeds dependant on the convienience of feed location, most at the ceiling rose as is the norm these days, in the case of my problem with the 3 way circuits it was because one circuit in the switch group was fed from a switch position another was fed at a ceiling rose and someone fitting replacement switch fronts had mixed up the wiring including the intermediate cross-over switch ( presume to try and cure the problem).

 

[Sawdust Sam]

My recommendation would be first to establish which of the wiring methods has been used to wire the two way switching. To do this, isolate the lighting circuit and then remove both switches. If both switches have two separate cables going into them (whether that be two twin and earth cables or one T&E and a separate single core cable then we can discount the four core cable method. If one of the switches only has one cable in it then that cable will be 3 core and earth.

The diagram shown on page one of this thread shows the two core method, ie two separate wires in each switch.

Once you’ve established which method is used then just google for either two core or three core 2 way lighting diagram.
Whichever method is used it’s almost certain that the wires between the two switches are in the wrong terminals.

Always isolate the circuit before moving wires around and if your not sure what your doing get a sparky in, shouldn’t take him more than 30 mins to sort the wiring out assuming my assumptions are correct.