Light Switch Keeps Tripping MCB Fuse - HELP!

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TheBigLebowski

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My brother recently decided to replace my lounge dimmer switch with an ordinary light switch. There is only one switch in the room which normally switches on 4 wall lights.

The old dimmer switch has been binned and long gone and now I am left with a shiny new 2WAY switch which has a COM, L1 and L2, although I have learned from this forum that I think I will probably only use this as a 1WAY switch.

There are four wires comming out of the wall, 1 is clearly the earth, 1 is the source (it is always live), 1 is the loop (if I connect this to the live my hallway light works if not it doesn't), finally the last one must be the switch live.

I have put both the source and the loop into the COM and the switch live into the L1 but whenever I switch the lounge lights on the MCB trips out.

Am I wiring everything up correctly?

Please help!
 
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if there is only 1 sw in room turning on 4 wall lights,you should have what we call 2core and earth at the switch(1 feed,1 sw wire),for some reason you have 3 core and earth.which is why i say 1 core maybe a neutral.Try connecting red cable to com,yellow to L1 and blue in connector.
 
Thanks for your response.

All three wires are red. 1 is always live, for the other two red wires I worked out which one was the "loop out" in order for the next light to work. This makes me believe that the last remaining red wire *must* be the "switched live".

My understanding is I am suppossed to have the always live wire and the "loop out" wire in COM then i should put the remaining red wire i.e. the wire I think is the "switch live" into L1.

But when I've done this, the MCB trips out.

It's seems like the constantly live and what I call the "switch live" just don't like being connected!

I really would appreciate anyones help in the best way to wire these bad boys up.
 
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Sounds like you have wired the switch correctly from your description, as you say 1. Live loop in 2. Live loop out 3. Switched live to lights. Try taking the bulbs out of the lights in case one of them has blown and caused a dead short, long shot I know but you need to start fault finding somewhere. If the fault still remains then try disconnecting the light fittings. Are you able to post a pic of the light switch wiring and the wall lights?
 
It seems like that should be right, you havn't done a dafty and screwed through the conductor with the faceplate pin?

from the sounds of it your wiring is in a conduit system right? perhaps the loop has pulled out the other end and is touching the conduit, or if it loops through the ceiling rose has snagged a sharp edge somewhere, and the tension on it of changing the switch has pushed it that last bit?

clutching at staws here, you need to do some insuation tests...
 
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Cheers guys! It's good to know it's not me going barmy!

This is the pic of the switch and one of the wall lights. It was myself who put the blue tape around the red wire so that I would remember it was the switched live. Also in the picture I have the switched live going into L2 however I have also tried it in L1 with no luck.

I may try and disconnect all wall lights next and see if the MCB still trips out.

In the meantime any other suggestions are welcome.
 
Some questions:

Have you tried it without the loop connection to the hall light?
You seem to have two cables, one with 2 reds and one appears to just be one red and earth. is that right?

In your situation, removing the wall light connections is a good fault finding method.

A minor point: you should link the earths on the back box to the earth on the switch plate otherwise you are relying on the fixing screws to make the earth connection between the two cables.
 
Thanks guys.

I said "four wires comming from the wall" as i was including the earth wire - sorry for any confusion.

I have tried it without the loop wire i.e.:

1. the loop wire connected to nothing
2. the live wire connected to COM
3. switch live connected to L1.

Unfortunately it still trips the MCB fuse. I've also tried taking all the wall light-bulbs out, still no luck.

I'm begining to pull my hair out now and I haven't got much left! :(
 
Including the earths the photo clearly shows 6 wires coming from the wall...

When the old switch was removed the earths were all connected together and/or to the earth terminal on the switch and/or back box, were they?


Anyway - I think you're going to need to get an electrician..
 
TTC's rule for changing a light switch:

Before disconnecting anything - take a photo of the connections and/or make detailed notes of what goes where.
 
silly question i know,but are you screwing back switch plate when reseting mcb.cos 1 of the cables might be tight against the back box and causing a live to earth fault which you are getting(no rubber gromet)
 
You guys are right.

There are 3 cables in grey sleeving each containing a single red. I know it's not clear from the pic but there are 2 cables at the top, 1 cable contains the red wire which is the live and the other cable contains the other red wire which is the switch-live. The cable comming from the bottom contains the red wire which is the loop.

Both of the cables from the top have their earths sleeved as one and screwed into the metal back box and the earth from the bottom cable is screwed into the earth plug of the brass switch itself. The earths were like this when the original dimmer switch was installed.

Having talked to my wife, she seems to recall the MCB fuse tripping out when she replaced a light bulb, which then cause the dimmer switch to stop working. This is the reason why my brother originally decided to replace the dimmer.

Having talked about it with you guys (i.e. the experts) and given what my wife said I think my money is on one of the wall lights either having a loose wire or being caput!

I'll try and take all wall lights off and test before the kids get home from school.

Will let you know how I get on - Wish me luck! :)

PS Kibeth, No I'm not screwing the brass switch on. Im testing it while it's still unscrewed from the back plate.
 
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