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wrote:

Hi,

I am having a problem with double light switch in my kitchen...and
would appreciate any advice before I call out an electrician.

In the kitchen I have a double switch (in a single gang faceplate) that
separately operates a ceiling light and a set of under cupboard lights.
The kitchen was rewired by an electrician about 6 years ago when we had
a kitchen fitted.

For a while this one switch has been playing up - depending on how
hard/fast you switched off the under cupboard lights would either blow
the lighting circuit fuse (5A) or possibly trip the whole house circuit
- I say possibly because I have recently fitted a plug in trip fuse for
the consumer unit (just on this lighting circuit) to avoid having to
fit a new 5A fuse in the dark each time the fuse went - and now the
house earth leakage circuit breaker trips out as well.

This week the switch has started tripping the electric almost every
time it is used.
There is some soot/ burning to the inside of the undercupboard switch.

The new fuse/trip device in the consumer unit is the only change.Thsi
repalced the old style 5Amp fuse holder at the consumer unit with a new
plug in trip type which was at 6A (Wylex to match consumer unit). This
was to avoid having to replace the fuse which used to go in the
lighting circuit when the undercupboard lights

On inspection of the switch wiring there are two cables entering the
switch backplate - both earths are connected to the metal back box. On
the switch for ceiling light cavle ones red and black wire are
connected to switch one COM and L1. There is a jumper wire from this
switch L1 to switch 2 L1. The 2nd incoming mains cable has the neutral
cable taped up (not connected) and the red cable enters switch 2 COM.

There is a junction box above the kitchen cupboard that the electrican
has used to extend the old switch cable to the current position. On
inspection the two switch cables (from switch back box) go to this
junction box and connect separately to two further cables that go to
the ceiling (upstairs floor ) - connections in this junction box are
cable1 neutral to neutral / cable 1 live to live ; and cable2 neutral
to neutral and cable2 live to live. Earths are all connected together.
This junction box looks to do no more than extend the switch cable run,

The cable to the ceiling light is just that - a junction box / ceiling
rose is not visible. When the kitchen was rewired the electrians had
the floor in the bedroom above the kitchen up so I presume any
junctions boxes are under the floorboards...and I haven't considered
removing the carpet / floorboards yet to look for them. .

any fitting with any signs of charring at all should be replaced,
however slight.

I guess my questions are ...
- Does the cabling sound right (jumper etc from switch 1 to switch 2)

that'll be the unswitched live

- Any ideas what would cause it to trip ...(this happens even if all
the undercupoard lights are turned off (they each have a built in
switch).

since both mcb and rcd trip, sounds like a toast situation. Find out
whats toasted and replace it before something catches fire.

- Should I go back to the old style cartidge fuse ?

no

The trip unit on my house wiring is an earth leakage circuit breaker
(my earth comes from a ground rod) .

You need to find out where the fault is. Trips on switch off typically
result from a switch being in the neutral line. You can use a
multimeter (in most cases) to find what is conducting slightly when it
shouldnt be. Maybe switch, light fitting, or cable. With item under
test disconnected, measure from earth to L&N connected. Also measure L
to N with bulb removed. You should get no conduction anywhere if things
are ok.

Obviously turn supply power off before disconnecting anything, leave
alone if you dont know what youre doing etc.

But dont leave it like this, it sounds like a fire starter.

NT