Yet another 2W lighting conundrum (and why I don't like domestics again)

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Another simple - just change a light switch job.

Customer reports a big flash, tripping and lights not working.

I arrived to find an obvious brand new 2G switch with a big black flash mark and didn't move properly. Customer insists it has not been touched despite some debris below on the otherwise clean carpet.

I found 5 cables, only No5 having an earth wired with cables 4&5 going off to a couple of 1G switches thus:

upload_2019-10-9_14-54-2.png

I noted the connexions and numbered cables as above then removed the faulty 2G switch
Cable 1 = 40Ω r-bk, 2Ω bk-earth, 43Ω r-earth. (Main switch in fuse board removes earth readings)
Cable 2 = 120Ω r-bk
Cable 3 = 41Ω r-bk, 76Ω y-bk, 139Ω r-y
Cable 4 and switch buzzed out perfectly
Cable 5 and switch buzzed out ok except grey was open circuit and switch didn't move properly.

The 2 associated ceiling roses looked like they are from the 60's with untold layers of paint, as is much of the installation.

And to crown it all there was a power cut.

I have fixed this and sent a report to the managing agent pointing out the importance of regular reports and the need for updating what's installed.

Ideas anyone?
 

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I think the switch that was messed with goes between 4 and 5


is this the clue then?

"No5 having an earth wired with cables "

The earth was connected to the live connections ?
 
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I am with Secure.

What are we looking for?
Are the stars connections? If so, why not use the switch terminal on the lower circuit?

Upper looks like a conventional two-way circuit (even though three strappers) with 2 black connected to switched live.
Lower looks like a conversion two-way circuit with 2 red and 3 red connected to the common strapper.
 
Cable 1 buzzed out as the supply and by going round the house found one light switched on, I took this to be 'loop in'.

checking cable 2 for resistance I found there are 2 additional lights, I took this to be 'loop out'.

After I took the resistance readings on cable 3, by removing the bulbs relevant to the 2G switch and found the yellow is a 60W bulb for the upper switch and the red is a 100W bulb for the lower switch on a common black neutral.

As I renewed the switches I found: Red of cable 4 is too short to reach 'lower com' and black of cable 5 is too short to reach 'upper com' to do the 3 strapper method.

by making it 3 connexions different (and one extra joint) to how I found it, this works:
Detling 2G 2W switches solution.gif

I had a 300VA interter with me and managed to function test.
 
I had some red white and blue three core but sadly lost it.
 
Say what you like about older wiring, but those dove-tailed ply-backed boxes were very nicely made.
 

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