In an earlier contribution to this discussion,
Alexei wrote:

Here a full account of what I've been trying to do.

I am installing a new pendant light. To this end, I've disconnected
the existing (working) light, and wired the new light, connecting red
to brown, black to blue and the third wire to both green/yellow and
the mounting bracket (the pendant is mostly metal).

This seemed to work perfectly. I've left the light on for about 15
minutes, after which the switch at the consumer unit tripped. I've
checked the bulbs, suspecting one might have blown, but all appeared
OK. I've turned the trip switch back on, but the light wouldn't work.

I suspected the dimmer switch may have been to blame. I disconnected
it to take a look and it looked dead (evidence of smoke).

I replaced the switch with a 450W-rated dimmer (the load is 5x60W, the
old dimmer was rated for 400W), wiring black to C and red to L1. The
new one died exactly the same death the moment I tried to turn it on.

At this point I've removed both the light and the switch to see if
I've managed to screw something up, but everything looks OK as far as
wiring goes: all the wires are connected where I intended them to be
connected, there is no exposed wiring, etc.

Messing about with the tester was just a quick sanity check; I didn't
realise they are unreliable. Stuart's comment about lack of
professionalism is a fair one; however, it is worth bearing in mind
that this is a DIY forum and I felt perfectly up to this relatively
straightforward job.

I am probably going to get a qualified electrician to sort this out.
In the meantime I would be most interested to hear what steps you
would take if you were trying to figure this out.

Thanks
Alexei

A neon tester can pick up induced voltages in wires which run parallel to
live wires, and which are *not* actually live. Far better to use a
voltmeter - or a multi-meter set to an appropriate scale for measuring 240v
AC.

It's possible that your dimmer switches don't like the type of load you're
giving them even though, in theory, they have more than enough capacity.
have you checked what happens when you use a bog standard on-off switch
rather than a dimmer? It's easier to get it working with an ordinary switch
first, and then worry about dimming, later.
--
Cheers,
Set Square
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