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

[sythai]

Hi Guys

Recently swapped over few faceplates. Some of them being a 3way lighting circuit.

Customer mentioned today have slight issue, looks like I've got a wire the wrong way round !

• when intermediate switch is in position 1, they 2x other switches don't activate the light.
• when intermediate switch is in position 2, all works fine.

The ways it's been wired must back to a JB somewhere (which assuming will have live/ s-live in there also) which I'm trying to avoid having to hunt down if poss.

All I have at switches:

• switch 1 : 3c TE
• switch inter : 2 x TE
• switch 2 : 3c TE

Odd one one really, sure its something really simple.
Have had it before where strappers at inter are wrong way round and you cant get lights to turn off.

Any ideas please, what I am not seeing ?

Even just had a go trying re-create the fault on my garage rig with no luck.....

Cheers Sy (hot and bothered today ?)

 

[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.)