Replacing Ceiling Rose on 2 Way Switch Hell !!

[MULLY]

Hi there,

Thanks in advance.

I recently have been putting up some new lights , everything was fine til the last one ! I didn't touch the switches at all just the ceiling rose what I have is;

Bottom Stairs switch;
3 Core cable containing 2 red core and 1 earth, and a seperate cable with a single red core. The two red cores are connected to the L1 & L2 portions of the switch while the single red core goes to the bit marked Common. Earth is earthed.

Top Stairs;
3 Core cable containing 2 red core and 1 earth, and a seperate cable with a single black core. The two red cores are connected to the L1 & L2 portions of the switch while the single black core goes to the bit marked Common. Earth is earthed.

Ceiling Rose;
3 Core cable containing 1 red core, 1 black core and 1 earth, and a seperate cable with a single black core.

How do I connect this up ? have tried a few things with the result that I've blown the fuse twice and had the light in the permanent on position regardless of switch any ideas for the ceiling Rose wiring ??

Many thanks
Mully

 

[MANDATE]

There are different methods of wiring a couple of two way switches.
Method (a) uses a 3 core cable plus earth between the switches.
Method (b) uses a 2 core cable plus earth between the switches.
(a) is the more popular because the live input wire and the switched live output wire are both connected to the same switch.
You have method (b) which works like this.
A live (red) is connected to common on your bottom switch, electric passes to L1 or L2 depending if the toggle is up or down.
L1 and L2 on your bottom switch is connected to L1 and L2 on your top switch by the two red wires.
In reverse order electric passes to common on your upstair switch depending on the toggle position.
Then from the common you have a black wire(with red flag) known as 'switched live'
This switched live then goes to your ceiling rose, from there down to the light bulb.(brown)
It continues from the bulb back to the rose( blue) and from the rose back to your fuse box(black). all wires after the bulb are neutral.

If you have not touched the switches your problem is at the ceiling rose and electric has gone straight to the neutral without going through the bulb and you have created a short circuit.
In your case you would only require two wires at the ceiling rose, that is the 'switched live'(black with red flag) and the neutral(black) both connected to the bulb, so it's not clear of the purpose of the red wire.
or what it is connected to.
I would remove fuse then disconnect the wires and keep them seperated, then replace fuse and check each wire with electricians voltage tester with one of the switches in the on and then off position.
One of these wires will only be live when the switch is operated(switched live) and One will never be live(neutral)
You could check your single red wire at the bottom switch and the single blackwire at the top switch to verify the red is always 'live' and the black is only live when switches are operated.
I say this because neutral wires(black) don't normally go back to the fuse box directly, it's common practice to wire the neutral to the neutral of the previous light, which could account for two blacks, but if that was the case then could the red be the switched live.
Unfortunately you didn't explain in detail how you had them connected when you had them permanently on or when they shorted.
Hope this explanation helps you fathom out which wire is which,sometimes just drawing the switches and making your own wiring diagram helps

 

[MULLY]

Many thanks for that.

I discovered that the spare red coming from the 3 Core Cable into the ceiling Rose is a permanent live. When I terminated this in a spare block everything worked fine as per method (b).

All the best
Mully