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So iv managed to find some time to crudely draw out the wiring.

You will have to forgive my poor knowledge on lighting circuits. For some people it's easy, for me it's always been a headache. Plus I hardly ever work on lighting wiring.

So, I think what we have here is 2 circuits with switch drops from both upstairs and downstairs lighting, via the red and black at each 2 gang 2 way.

The bit I cant fathom is, why are the colors for the intermediate red and black?

Have I missed something? Is the red and black in the 2 ways not a switch/perm feed?

Voltage on light circuit when off 20200521_100141 - EletriciansForums.net
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Voltage on light circuit when off 20200517_121812 - EletriciansForums.net

Voltage on light circuit when off 20200517_121721 - EletriciansForums.net

Voltage on light circuit when off 20200517_121244 - EletriciansForums.net

some more photos.

may help
 
From your sketch, it looks like perfectly normal 'conversion' 2-way with the strappers in 3C+E, where someone has later broken into the runs of strappers and extended them to a new intermediate position using T+E. Since only L1 & L2 need to go via the intermediate (com just carries on through the break-in point as before) they used T+E not 3C+E.

I would say it's a scenario in which the capacitive leakage is likely to be quite high. Lots of cable runs with lots of PL and SL cores near each other.
 
I think your right.

If you drop one of the blue strappers out, the flashing stops but obviously you loose some functionality between switches.

So snubbers are the way forward?
 
Yes, but just to be sure that the leakage is not (at least partly) due to damaged cables, I would do some quick IR checks especially between PL and SL including between the two switch groups. My method for that would be to do a normal test L & N to E first with the switches in an 'on' permutation, then:

  • Switch one switch over to create an 'off' permutation
  • Disconnect PL and SL in both roses, earth both PL and SL in the upstairs rose and SL in the downstairs.
  • IR test the downstairs PL to earth, obviously if it shows zero resistance the switches are back in an 'on' permutation so flip one over.
  • Switch over both 2-ways leaving the intermediate as-is and test again, to ensure all strappers are tested against common.
  • Earth the downstairs PL, un-earth the upstairs PL.
  • Repeat steps 1-3 at the upstairs rose.

If you can't get to the roses you can do it all from the 2-ways by disconnecting the switch drops but leaving the strappers in L1 & L2. However, the switch drops are not then included and there is more of a risk of something getting disconnected and missed. It takes longer to describe than it will to do. Basically by earthing all conductors except one PL or SL you are testing the insulation on that relative to everything else of interest. If all results are good then crack on with snubber loads.
 
Yes, but just to be sure that the leakage is not (at least partly) due to damaged cables, I would do some quick IR checks especially between PL and SL including between the two switch groups. My method for that would be to do a normal test L & N to E first with the switches in an 'on' permutation, then:

  • Switch one switch over to create an 'off' permutation
  • Disconnect PL and SL in both roses, earth both PL and SL in the upstairs rose and SL in the downstairs.
  • IR test the downstairs PL to earth, obviously if it shows zero resistance the switches are back in an 'on' permutation so flip one over.
  • Switch over both 2-ways leaving the intermediate as-is and test again, to ensure all strappers are tested against common.
  • Earth the downstairs PL, un-earth the upstairs PL.
  • Repeat steps 1-3 at the upstairs rose.

If you can't get to the roses you can do it all from the 2-ways by disconnecting the switch drops but leaving the strappers in L1 & L2. However, the switch drops are not then included and there is more of a risk of something getting disconnected and missed. It takes longer to describe than it will to do. Basically by earthing all conductors except one PL or SL you are testing the insulation on that relative to everything else of interest. If all results are good then crack on with snubber loads.

I cant get to the Rose's. The 2d fittings only have L/N/E coming through the ceiling so I'd imagine the Rose's are in the void somewhere.

I'll order some snubbers then. Is there any specific type? Rating? Spec?
 
Just about to order snubber from cpc.

How are they connected into the circuit? Across live loop and neutral at the rose for upstairs and the same for downstairs?
 
In parallel with the lamps, at any convenient point in the circuit.
 
One per switched line, it's bleeding off the leakage from SL to N instead of it passing through the lamp(s).
 
No, only one per SL regardless of how many lamps it serves, as they are all in parallel. The snubber can be placed anywhere - at one of the lamps, in the rose, in a JB where the SL and N are accessible - to bleed that SL down to N and therefore stop any and all lamps on that switch flashing.

Does anyone have experience of what value of capacitor is typically needed? I would expect 0.1μF to be fine, Xc is about 32kΩ at 50Hz, so even 100's of μA of leakage would only produce a few volts at the lamps.
 
One per switched line, it's bleeding off the leakage from SL to N instead of it passing through the lamp(s).
No, only one per SL regardless of how many lamps it serves, as they are all in parallel. The snubber can be placed anywhere - at one of the lamps, in the rose, in a JB where the SL and N are accessible - to bleed that SL down to N and therefore stop any and all lamps on that switch flashing.

Does anyone have experience of what value of capacitor is typically needed? I would expect 0.1μF to be fine, Xc is about 32kΩ at 50Hz, so even 100s of μA of leakage would produce a few volts at the lamps.

Does it make an difference that there are 2 circuits effected?

Should it be 1 snubber per SL and N, for each circuit?
 
Yes. Each SL is a separate, floating 'leakage collector' when it is switched off. It needs to be bled down to its own neutral.
 
Probably switch on the Neutral and not the live, quite dangerous really.

Why do you think the switch is in the neutral? Apologies if I've missed something.
 
Probably switch on the Neutral and not the live, quite dangerous really

Unlikely, since in post #9 they reported the switched feed to be 230V from earth with the lights on, and 79V from earth with them off.
 
Sorry I thought he tested between Line and Neutral. I was going to suggest test between Live and Earth at light when switch off.

I have seen something similar and the Second switch was off the first Switch Live and Switch Line in T&E.
 
Have a google on snubbers, there are ready made ones available that will have the values stated on them.
 
0.1μF is common, I can't see that a larger value would be needed for any reasonable amount of leakage, and the larger case would be harder to fit in a back box or wherever it's going.

BTW did you ever do any insulation tests on the switching as I recommended? It would be good to confirm that you are not simply concealing an actual fault.
 

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