I am replacing a pendant light together with the light switch. I've
totally disconnected them from the mains wiring -- I basically have two
sets of three wires sticking out of the wall and out of the ceiling.

When I turn the power back on at the consumer unit, and use a mains
tester (screwdriver type) on the three wires sticking out of the
ceiling, all three are shown as LIVE.

This strikes me as very odd.

Is this necessarily indicative of a serious wiring problem somewhere?

Thanks
Alexei

Alexei wrote in message
.com...
I am replacing a pendant light together with the light switch. I've
totally disconnected them from the mains wiring -- I basically have two
sets of three wires sticking out of the wall and out of the ceiling.

When I turn the power back on at the consumer unit, and use a mains
tester (screwdriver type) on the three wires sticking out of the
ceiling, all three are shown as LIVE.

This strikes me as very odd.

Is this necessarily indicative of a serious wiring problem somewhere?

Thanks
Alexei


Neon type testers can give misleading results. To be certain if a wire is
live, connect one side of a (mains) light bulb to a known neutral and probe
the unknown wires with the other bulb connection.

Bob

This would explain it, thanks. Out of interest, under what
circumstances could a neon-type tester give misleading results?

I'll do the lightbulb test some other day, when there's sufficient
daylight.

On 2 Oct 2005 10:29:33 -0700,it is alleged that "Alexei"
spake thusly in uk.d-i-y:

This would explain it, thanks. Out of interest, under what
circumstances could a neon-type tester give misleading results?

If one or more of the cables that are disconnected is running parallel
to a live cable. If it's not actually a neon screwdriver but one of
the 'continuity testing and mains testing' Hypersensitive LED ones I
noticed B&Q have on clearance, the value of 'running parallel to'
changes to 'within spitting distance of'.


I'll do the lightbulb test some other day, when there's sufficient
daylight.


--
There is no reason anyone would want a computer in their home.
- Ken Olson, President of DEC, 1977

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

On 2 Oct 2005 11:17:36 -0700,it is alleged that "Alexei"
spake thusly in uk.d-i-y:

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

In your original post, you stated you had "two sets of three wires
sticking out of the wall and out of the ceiling."

Just to clarify, did you mean 'one set of 3 at the switch, and one set
of 3 at the lighting point' ?

If so, it sounds like you're connecting things up right, (although the
black at the switch should technically be sleeved red or brown).

If the fault is occurring with this apparently perfectly normal
wiring, you have 2 choices.

1) Call an electrician (guaranteed but pricy).

2) Try swapping parts, obtain a 'normal' lampholder and 60w lamp, and
a light switch of the 99p variety, and see if the fault recurs when
you swap them in. If it doesn't, the fault was in one of the 2 things
you just eliminated.

It sounds to me like one of 3 possibilities.

A) The new dimmer was faulty. (unlikely as a second also died the same
way)

B) The new light fixture is faulty (possibly caused during
manufacture)

C) The junction box (which must be present somewhere, probably above
the ceiling) has an intermittent short circuit, this should be
considered when trying 'turn it on and see' methods, not trying to
induce paranoia, but a slow smouldering fire under the floor is A Bad
Thing.

--
There is no reason anyone would want a computer in their home.
- Ken Olson, President of DEC, 1977

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
______
Please reply to newsgroup. Reply address is invalid.

On 2 Oct 2005 11:17:36 -0700, "Alexei"
scrawled:

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.

Well, evidently it's not straight forward enough.

Sounds like you've pulled down the old pendant, blatantly ignored the
loop in and switch wire connections and wired the light across the
live and neutral, in parallel with the dimmer switch, causing the
light to work and the switch to explode.

When you wired it up did the switch work and the light dim up and down
as it should?

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.

I would get my test meter out so we're stuffed at this point as you
haven't got one!
--
Stuart @ SJW Electrical

Please Reply to group

On 2 Oct 2005 10:29:33 -0700, "Alexei"
scrawled:

Out of interest, under what
circumstances could a neon-type tester give misleading results?

Whenever you use it.

I'll do the lightbulb test some other day, when there's sufficient
daylight.

If you're planning on doing any more electrical work it would be
worthwhile investing in a reasonable multimeter. You can pick up
something respectable from around £20.
--
Stuart @ SJW Electrical

Please Reply to group

If you're planning on doing any more electrical work it would be
worthwhile investing in a reasonable multimeter. You can pick up
something respectable from around =A320.

What would you be looking for in a multimeter for this type of work?

I use one of those for non-mains work:
http://www.maplin.co.uk/Module.aspx?...411&doy=3D2m10

However, I am not entirely sure whether it would be appropriate (or
even safe) to take it near the mains.

Alexei

On 2 Oct 2005 12:00:34 -0700, "Alexei"
scrawled:

If you're planning on doing any more electrical work it would be
worthwhile investing in a reasonable multimeter. You can pick up
something respectable from around £20.

What would you be looking for in a multimeter for this type of work?

I use one of those for non-mains work:
http://www.maplin.co.uk/Module.aspx?...25411&doy=2m10

However, I am not entirely sure whether it would be appropriate (or
even safe) to take it near the mains.

No, me neither.

I've used AlphaTek for some good cheap meters in the past. Robin also
do an autoranging rugged DMM for £20 odd (I think, I could be making
that bit about Robin up).

As a side note, it's a pity Maplin can't spell 'professional' (as in
proffessional multimeter, down on the left).
--
Stuart @ SJW Electrical

Please Reply to group

In an earlier contribution to this discussion,
Alexei wrote:

If you're planning on doing any more electrical work it would be
worthwhile investing in a reasonable multimeter. You can pick up
something respectable from around £20.

What would you be looking for in a multimeter for this type of work?

I use one of those for non-mains work:
http://www.maplin.co.uk/Module.aspx?...25411&doy=2m10

However, I am not entirely sure whether it would be appropriate (or
even safe) to take it near the mains.

Alexei

If you click on 'Spec' in the above reference, it gives you the ranges
covered - one of which is 600v AC - so it's obviously designed to cope with
mains.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In article ,
Lurch wrote:
Out of interest, under what
circumstances could a neon-type tester give misleading results?

Whenever you use it.

I'll do the lightbulb test some other day, when there's sufficient
daylight.

If you're planning on doing any more electrical work it would be
worthwhile investing in a reasonable multimeter. You can pick up
something respectable from around £20.

Trouble is modern DVMs have such a high input impedance that they too can
give misleading results on open circuit mains cables. Older mechanical
meter AVOs had an input impedance of around 1000 ohms per volt which is
low enough not to show odd results. So if only needing a meter for
domestic mains etc an analogue one might be a better bet. But then cheap
ones have test prods etc that aren't really ideal safety wise for the
rough and tumble of live mains work. ;-)

--
*Pentium wise, pen and paper foolish *

Dave Plowman London SW
To e-mail, change noise into sound.

In message .com,
Alexei writes
This would explain it, thanks. Out of interest, under what
circumstances could a neon-type tester give misleading results?

Almost any - chuck it away and buy a meter


I'll do the lightbulb test some other day, when there's sufficient
daylight.


--
geoff

On Sun, 02 Oct 2005 20:00:08 GMT, raden wrote:

In message .com,
Alexei writes
This would explain it, thanks. Out of interest, under what
circumstances could a neon-type tester give misleading results?

Almost any - chuck it away and buy a meter

Actually an "electronics"-type meter can be just as misleading as a
neon screwdriver. If it has a very high input impedance it won't load
the circuit under test - just like a neon.
A much better bet would be a meter with much lower ohms-per-volt.

--
Frank Erskine

Actually an "electronics"-type meter can be just as misleading as a
neon screwdriver. If it has a very high input impedance it won't load
the circuit under test - just like a neon.
A much better bet would be a meter with much lower ohms-per-volt.

The one I have has input impedance of 1MOhm, which certainly appears
high.

Could anyone recommend any specific models of multimeters that would be
suitable for this type of work, as well as good vendors (online or
otherwise)? Something around =A320-=A330 mark would be good.

Thanks
Alexei

Alexei wrote:

This would explain it, thanks. Out of interest, under what
circumstances could a neon-type tester give misleading results?


capacitative coupling to any mains source.

E,G, a bit of T&E lying next to a live cable will show 'hot' on all its
wires.


Its a useful feature or a curse depending.

I'll do the lightbulb test some other day, when there's sufficient
daylight.

On 2 Oct 2005 09:35:50 -0700, "Alexei"
scrawled:

I am replacing a pendant light together with the light switch. I've
totally disconnected them from the mains wiring -- I basically have two
sets of three wires sticking out of the wall and out of the ceiling.

When I turn the power back on at the consumer unit, and use a mains
tester (screwdriver type) on the three wires sticking out of the
ceiling, all three are shown as LIVE.

That's because the neon screwdriver method of testing is absolutely
useless. It goes in the usefulness file along with cheap stud and pipe
detectors.

This strikes me as very odd.

Nah, quite normal. It'll probably tell you your elbows live but fail
to tell you a live cable is live.

Is this necessarily indicative of a serious wiring problem somewhere?

Serious lack of professionalism tbh. Get a proper tester on the job.
--
Stuart @ SJW Electrical

Please Reply to group

There is one more detail that just came back to me.

When I was removing the old dimmer, I am pretty certain that the three
wires (red, black and uninsulated) were wired to the three terminals on
the switch (C, L1, L2 - it was a 2-way switch used as 1-way).

This is not a setup I've encountered before. Have you seen a setup like
this? Is it even standard?

In retrospect, I should have noticed the unfamiliar wiring, and at
least noted it down...

Alexei

On 2 Oct 2005 13:26:37 -0700,it is alleged that "Alexei"
spake thusly in uk.d-i-y:

There is one more detail that just came back to me.

When I was removing the old dimmer, I am pretty certain that the three
wires (red, black and uninsulated) were wired to the three terminals on
the switch (C, L1, L2 - it was a 2-way switch used as 1-way).

This is not a setup I've encountered before. Have you seen a setup like
this? Is it even standard?

Absolutely not, at this point, I am going to say 'call an electrician,
and NOT the one who did this'

In retrospect, I should have noticed the unfamiliar wiring, and at
least noted it down...

Alexei


--
There is no reason anyone would want a computer in their home.
- Ken Olson, President of DEC, 1977

On 2 Oct 2005 13:26:37 -0700, "Alexei"
scrawled:

There is one more detail that just came back to me.

Hang on then, here we go!

When I was removing the old dimmer, I am pretty certain that the three
wires (red, black and uninsulated) were wired to the three terminals on
the switch (C, L1, L2 - it was a 2-way switch used as 1-way).

Something not right there. Sounds like a muppet fitted it, or it
appeared to be connected like that but in actual fact wasn't. Was it a
brass dimmer, was the uninsulated (which should be sheathed with
green\yellow sleeving, actually connected to an earth terminal on the
plate?

This is not a setup I've encountered before. Have you seen a setup like
this? Is it even standard?

No, if it was as you say it was non-compliant and wrong, and possibly
dangerous.

In retrospect, I should have noticed the unfamiliar wiring, and at
least noted it down...

Might have been an idea. Next time, utilise the functions of the
digital camera first
--
Stuart @ SJW Electrical

Please Reply to group

When I was removing the old dimmer, I am pretty certain that the three
wires (red, black and uninsulated) were wired to the three terminals on
the switch (C, L1, L2 - it was a 2-way switch used as 1-way).

Something not right there. Sounds like a muppet fitted it, or it
appeared to be connected like that but in actual fact wasn't. Was it a
brass dimmer, was the uninsulated (which should be sheathed with
green\yellow sleeving, actually connected to an earth terminal on the
plate?

No, the dimmer was a plastic one fitted onto a metal backbox. I am
pretty sure none of the three wires were connected to the terminal on
the backbox.

However, it is not impossible that my memory is wrong.

Alexei

On 2 Oct 2005 09:35:50 -0700, "Alexei" wrote:

| I am replacing a pendant light together with the light switch. I've
| totally disconnected them from the mains wiring -- I basically have two
| sets of three wires sticking out of the wall and out of the ceiling.
|
| When I turn the power back on at the consumer unit, and use a mains
| tester (screwdriver type) on the three wires sticking out of the
| ceiling, all three are shown as LIVE.
|
| This strikes me as very odd.
|
| Is this necessarily indicative of a serious wiring problem somewhere?

Get a domestic multimeter Maplins sell them for GBP3 in the stores.

--
Dave Fawthrop dave hyphenologist co uk
The London suicide bombers killed innocent commuters.
Animal rights terrorists and activists kill innocent patients.