1 Pendant - 2 Switch Issues

Sin_Chase

Sin_Chase

Sin_Chase

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Joined
13 Jan 2004
Posts
21,263
Evening all. Having a mare with some multiway switching for lights in a flat I am decorating. I've just troubleshooted and fixed one of the rooms. It has 3 core red/white/blue cabling to two switches which were wire nutted in the pendant. Eventually figured out the original 3 way switching with supply at the pendant had been messed up and reinstated it, works as expected.

I've now got a 2 switch 1 pendant arrangement in the stairway which is not working.

Switch 1
Downstairs light switch
1 x 3 Core red/white/blue

Switch 2
Upstairs light switch
1 x 3 Core red/white/blue
1 x twin and earth red/black/bare

Pendant
1 x twin and earth red/black/bare

As a note there is no earth wired into the lighting circuit (I know, but I'm not running new cabling to facilitate this) This has made taking multimeter measurements difficult. However, I've measured some voltages between the bare disconnected cables and they are as follows:

Switch 1
Red - Blue = 156v
Red - White = 150v
Blue - White 9v (Phantom?)

Switch 2
Red - Blue = 72v
Red - White = 11v (Phantom?)
Blue - White 85v

Black - Red = 0v (twin and earth back/red/bare)


I've done some continuity testing and found the following continuity:
Switch 1 White - Switch 2 White
Switch 1 Red - Switch 2 Blue
Switch 1 Blue - Switch 2 Red

This baffled me a little as I SUSPECTED initially there was a two way switching arrangement with power in the pendant. Clearly there is no power supply in the pendant owing to the single twin and earth present. I'm struggling to identify which switch is housing the supply. I am also struggling to ascertain what king of cabling arrangement this is, some kind of 3-way as per the fixed bedroom? I am also a little baffled why the red and blues in Switches 1 & 2 have swapped continuity, as if they are two separate runs of 3 core with red and blue swapped in wire nuts/bonds elsewhere behind the wall.

Image of what cables I have presented where at this time:
flat-switchissue1.jpg


Anyone got any ideas where to start?
 
****Be extra careful if this is landing / stair light as may have borrowed neutral and might need to turn both up and down lights off to be safe, best to get electrician if your not confident.****

Wrote long reply which was hard to follow so....couldn't think of an easy way to dead test this..only having 1 cable at the pendant complicates things, maybe be wired junction box method or does it just turn on 1 pendant or does it do 2 at the same time? hall and landing etc? then the loop maybe at the other pendant and this is just slaves off it to come on at the same time.

Short version - put a bulb in pendant + link red & black from 2 core by putting them both in the same switch terminal and turn power on to see if that works

If it does then just need to put 3 core in the same terminals at both switches and put red / black into L1 / L2

so

switch 1
com - white
L1 - red
L2 - blue

switch 2
Com - white
L1 red and red
L2 black and blue

etc
 
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That was the most common way of wiring this but the voltages you were getting and the continuity make me suspicious that there could be a jb in the 3 core between the 2 switches feeding power in or some other odd arrangement

How was the other room wired, if both original wiring then same method should be used for both
 
Thanks for the reply.

I'll give that method a try and report back! Pulling my hair out with it, I suspect you are right in that there is a junction box hidden away somewhere which only serves to complicate troubleshooting someone else's work.
 
It's a single pendant in the stairs, the two switches are placed at the top of the stairs and the bottom. There are no other switches / pendants in this area. Curiously the bottom switch was a double gang, but nothing was cabled into the second switch nor was there any spare cabling to go into it even if you wanted to. Suspect someone put a 2 gang on because they didn't have a single....

There is only a single 6A lighting circuit for the whole flat. I'm isolating everything including the feed to the CU when working on it.


The other room is wired as follows:

Switch on wall:
L3 white
L2 blue
L1 red

Pull cord switch on roof:
com white (originally into earth, lol?)
L2 blue
L1 red

At Pendant:
3 core blue bonded in wire nut
3 core white bonded in wire nut
Two red bonded in wire nut (assuming one from T&E and one from 3 core)
1 black and 1 red into pendant
 
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Yeah the other room sounds different, hope the stairs are more standard wiring because of the 2 core red/black at the switch, if they used the same method it would probably just have a 3 core at each end

for that room instead of running 3 core direct from switch to switch they have run through the pendant to avoid having to pull an extra cable down to a switch or save copper

some older installations have some odd methods, some are cable saving methods, just not the most straight forward way of doing it... well not straight forward if your used to the modern way of doing things
 
Connected the red/black in the T&E and powered up Light doesn't come on. Would appear the source is somehow being delivered on the 3 core in a junction from elsewhere...
 
Putting switch 2 back to how it was wired before enables the light to turn on but switch 1 needs to be 'on' and then switch 2 can turn the light on and off .

That's with Switch 2 having the T&E Black connected to the 3 core blue in a connector block (which was how it was when I opened it up.

If I swap the L1 and L2 around in one of the switches it merely flips the behaviour such that switch 2 needs to be on and Switch 1 can turn the light on and off.

I'm still struggling to work out what the supply feed is and how this should be wired
 
Maybe it was always wired wrong? did it work properly as a 2 way before?

How is it wired at the moment, what colour is in each terminal at both ends? where is the red from the 2 core now?

Maybe try

com - red
L1 - white
L2 blue

Com red with red or black
L1 white
L2 blue

Maybe power is fed in via com on one switch and out via com on other switch, guessing red based on other room where white and blue just passed straight through, but the continuity for this room swaps red / blue to add confusion, could there be a 3rd switch an intermediate crossing over the blue / red?

Maybe 1 of the red/black in the 2 core is redundant and they could have just used a single but used a 2 core instead - ideally could use a continuity test between pendant red black and switch red black in all combinations to see whats connected

Any chance of finding the junction box to see how it is wired to save guessing?
 
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I'm unsure if it ever worked properly before.

No chance of finding the junction box without ripping holes in the ceiling and walls. No ceiling void as it's a flat roof flat. It's possible there is a junction box near one of the other 1st floor pendant or even ground floor but absolutely no indication as to where it might be.

There is a continuity if I probe the red black 2 core in the upstairs switch and if I probe from pendant black to 2 core black and red to red. I'm pretty sure the pendant has a single 2 core run to the switch and only the switch but it's possible it could be otherwise I guess.

I'm going to call an electrician in I think as the only thing I've got now is trial and error.
 
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