Bit of puzzler 3way.... any ideas please

[Mark Wright]

Presumably if it goes from 3core to T&E ? there is a junction box somewhere in the middle ? and it might be that the corresponding colours are not connected

also if it goes from 3core to T&E Red/Black how do you know If Red or Black is L1 or L2 ?

 

[sythai]

Lets hope it is a faulty switch, with that wiring setup its hunt the JB good luck.
IMO, 2way or intermediate through a JB is bad practice, all connections should be at switch points.
Have you tested all commons/ strappers for continuity.?

Was only a passing visit yesterday.... just had a go at swapping strappers around in every combination at the inter. Calling back next week with spare switch and ready to buzz out fully if so
[automerge]1591192532[/automerge]

It wasn’t bad practice back in the 70’S or 80’s It’s only now we’ve realised fitted carpets and laminate flooring causes the problems of locating them.
Just next to the hatch in the attic, or on the landing, near the top of the stairs. The floorboards are possibly cut as access to the jb. And if the boards have ever been up in the past, they’ll squeak or sound loose when walked on.

Replace the jb with an mf equivalent, and happy days

Luckily landing carpet is only loosely down (being replaced) and have spied a few screwed boards already ?️‍
[automerge]1591192621[/automerge]

Can I be the first to criticise the terminology?

Its 3c&e... not 3c t&e..... ie, a "3 core and earth"... not a "3 core twin and earth"

My bad ?

 

[Lucien Nunes]

also if it goes from 3core to T&E Red/Black how do you know If Red or Black is L1 or L2 ?

It doesn't matter which is L1 or L2 or how many times they cross over. Provided all the strappers are connected in some way, it will work. Unless you can find a flaw in my reasoning above, the fact that the 2-ways work correctly with the intermediate in one position proves that all the strappers and junction box connections are present and correct, i.e. the problem can only be within the intermediate switch itself. If anything else were wrong, one 2-way switch would disable the other either on or off in one position.

Unless I've missed something... please try to prove me wrong

Update: It's a challenge. Draw me a possible circuit showing a fault other than wrong connections at the intermediate or open-circuit contacts inside it, in which the 2-ways work correctly with the intermediate in one position, but they cannot turn the light on at all in the other.

 

[7029 dave]

It wasn’t bad practice back in the 70’S or 80’s It’s only now we’ve realised fitted carpets and laminate flooring causes the problems of locating them.
Just next to the hatch in the attic, or on the landing, near the top of the stairs. The floorboards are possibly cut as access to the jb. And if the boards have ever been up in the past, they’ll squeak or sound loose when walked on.

Replace the jb with an mf equivalent, and happy days

Yes I was not talking so much about JB methods in general, wired many lighting circuits this way, especially with occupied rewires, but was talking about the wiring of strappers/ commons for 2 way etc, no real reason not to have connections in the switches.

 

[Mark Wright]

Still not sure how it could go from 3core to T&E can someone draw it out?

I think it would make a difference because you would end up with L1 and L2 the wrong way round on the final switch and that would produce a problem like you say.

 

[7029 dave]

Can I be the first to criticise the terminology?

Its 3c&e... not 3c t&e..... ie, a "3 core and earth"... not a "3 core twin and earth"

Or tripple and earth

 

[littlespark]

I think we're getting away from the original question here. We've all given advice, and the OP will investigate when he returns to the job.
Hopefully something we've said will be spot on.... no point rambling over and over

 

[Mike Johnson]

Bloody ramblers they always leave the gate unlatched.

 

[Timbo]

Thanks Guys.... really appreciate all your help and hopefully me not going bonkers !! ?

I'm going along the lines of dodgy switch, best I take a spare one along along (Hamilton hartland grid it.)

Not back until next week so will report back then

I've attached a schematic of what I've got..... conversion method which all must end up a JB somewhere.

View attachment 58597

Just a point on your diagram - red was generally used as common connection, yellow / blue to L1 / L2. Have you checked continuity of cores to intermediate from each 2 way? Sorry if I've missed it.

 

[7029 dave]

Just a point on your diagram - red was generally used as common connection, yellow / blue to L1 / L2. Have you checked continuity of cores to intermediate from each 2 way? Sorry if I've missed it.

Common was either Red or Yellow round here, back in the day.

 

[static zap]

A DP switch would give the reported symptom with either 'conventional' or 'conversion' wiring.

.. I would be removing Intermediate sw first for some simple
continuiity checks in both positions !.
..makeing sure the world has not gone sideways ,- DP only -or- half a cross ! ..

 

[Mike Johnson]

Worst nightmare is a defective new intermediate switch, not once but twice on two separate installations.

 

[telectrix]

Can I be the first to criticise the terminology?

Its 3c&e... not 3c t&e..... ie, a "3 core and earth"... not a "3 core twin and earth"

Pedant.

 

[andyb]

One of the conductors at one of the the 2 way switches will be live when all the concuctors are disconnected. Surely this will give you the colours of the strappers and common on the other 2 way swtch.
Providng this is true, it should be easy to show whether the problem is in a switch or the jb.
I suspect the problem is in the wiring of the switches.

 

[sythai]

Well thanks Chaps for all your feedback and pointers along the way...... at least I'm not going fully bonkers after doing this for the last 20 yrs !!?

Went and sorted yesterday morning, couldn't handle the suspense anymore.

..... it was a dodgy intermediate, first time for me ?

 

[Mike Johnson]

As Post 32, happens more than we think.

 

[Lucien Nunes]

Glad it was an easy fix (and that I was the first to suggest it). As I mentioned in that post, either the intermediate switch itself or its connections were the only suspects if there was only one fault location, which is probable on something that was thought to have worked originally and did not go bang.

This fault is a good demonstration of a specific troubleshooting tactic: By all means consider the possible impact of suspicious circumstances (in this case, hidden JB, change in cable colours) in parallel with logical analysis, but if the two conflict, give priority to the logic. It's reassuring to potter about testing strapper continuity while muttering how the numpty used the wrong colour for the common and how the junction box should have been more accessible, but it was never on the troubleshooting pathway because the original observation (if accurate) proved conclusively that all connections were correct and functional everywhere but in the intermediate.

If that inference doesn't leap out at you intuitively, draw out the two possible circuits (conventional, conversion), simulate the plausible single wiring errors / faults / switch malfunctions (not all of which apply to both circuits) and see the pattern of results, mentally filling-in the 8-line truth table for the light according to the switch positions if necessary. There are about twenty realistic different faults / mistakes, not counting the mirror images of those (e.g a single broken strapper could exist in four different places, but due to symmetry the effect would be the same in each case and only one need be considered.)