Robin expressed precisely :
I'd be more impressed by your confidence if you'd bothered to state what you
are taking to be the purpose of a volt stick. (Note I never said I approved
the use of a volt stick to prove a conductor "dead". I do continue to fail
to see why you claim they are "always unsound in principle" to identify a
live conductor - eg when there are several conductors in a conduit.)

Volt sticks can vary in quality, Fluke sells one of the better ones. If
there are multiple live wires around it is possible your test wire
might show as being live - the simple solution is to shield the stick
from all but the wire you are interested in with your fingers. The
validity then needs to be crossed checked with something which actually
draws some current from the source. A test lamp works well for this.

I have never known a Fluke show a circuit as being dead, when it is
live, but the stick should always be tested before use. One test is to
rub the tip of the stick up and down your arm, whereupon it should
light up. They are absolutely great for non-invasive tests, but only if
you are practised in using one.

Andy Burns wrote:

I don't remember mine (Kewtech) warning about not detecting live SWA
cables

Though I see the instructions for a newer model do

On 04/12/2017 08:02, wrote:
Hi John

That's a good point. When the power was on it had a more or less
continuous beep. When the power was off the beep was more of a
series of individual beeps. The thing that spooked me more was the
self test seemingly not working.

I have never tried that brand, and so can't really compare against my
experience. I have a similar looking thing by Fluke that I find to be
reliable.

Generally if you follow the instructions - i.e. test against known live
and known dead before trusting a reading they should be ok.


--
Cheers,

John.

/================================================== ===============\
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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Monday, 4 December 2017 10:43:27 UTC, John Rumm wrote:
On 04/12/2017 05:18, tabbypurr wrote:
On Monday, 4 December 2017 00:10:01 UTC, John Rumm wrote:
On 03/12/2017 17:41, tabbypurr wrote:
On Sunday, 3 December 2017 17:31:31 UTC, wrote:

If this type is so unreliable what is the safest way to determine if a cable is safe to cut?

voltmeter

Not exactly "non contract" though is it!

No. Is that an issue?

Yes! The whole purpose of the volt stick style detector is that it can
make an assessment without needing any direct contact to the circuit,

yes

and so avoids all the risks associated with that.

it creates a bigger risk by misinforming users on occasion that a live cable is dead.

Also keep in mind that a false positive reading is equally possible from
a high impedance volt meter.

not from a standard multimeter. Especially high impedance ones are a different fish of kettle.


NT

On Monday, 4 December 2017 10:44:50 UTC, John Rumm wrote:
On 03/12/2017 23:08, tabbypurr wrote:

you could always read up on how they work and why they give false negatives and false positives.

If you use them according to the instructions, you should not get false
negatives.

The reality is it does happen. I've explained why.

On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...

On 04/12/2017 12:59, wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent faults?

--
Robin
reply-to address is (intended to be) valid

On Monday, 4 December 2017 13:22:00 UTC, Robin wrote:
On 04/12/2017 12:59, tabbypurr wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent faults?

No, but it does require me to plonk people that lack expertise yet keep arguing.


NT

On 04/12/2017 13:42, wrote:
On Monday, 4 December 2017 13:22:00 UTC, Robin wrote:
On 04/12/2017 12:59, tabbypurr wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent faults?

No, but it does require me to plonk people that lack expertise yet keep arguing.



Then why not tell me a volt meter which is incapable of giving a false
negative and prove me wrong?



--
Robin
reply-to address is (intended to be) valid

On Monday, 4 December 2017 13:59:10 UTC, Robin wrote:
On 04/12/2017 13:42, tabbypurr wrote:
On Monday, 4 December 2017 13:22:00 UTC, Robin wrote:
On 04/12/2017 12:59, tabbypurr wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent faults?

No, but it does require me to plonk people that lack expertise yet keep arguing.



Then why not tell me a volt meter which is incapable of giving a false
negative and prove me wrong?

try sci.electronics.basics

On 04/12/2017 12:55, wrote:
On Monday, 4 December 2017 10:43:27 UTC, John Rumm wrote:

Also keep in mind that a false positive reading is equally possible from
a high impedance volt meter.

not from a standard multimeter. Especially high impedance ones are a different fish of kettle.

You have that back to front. High impedance meters are the norm. Any
common digital multimeter will likely have an input impedance in the
megohms range, and that is high enough to see capacitively coupled
floating conductors as live.

This is why test gear makers specifically make kit for mains test
applications that have low or adaptive impedance measurement options to
eliminate these spurious readings.

Goo look at the specs for something like a Fluke 114, or 115


--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/12/2017 12:57, wrote:
On Monday, 4 December 2017 10:44:50 UTC, John Rumm wrote:
On 03/12/2017 23:08, tabbypurr wrote:

you could always read up on how they work and why they give false negatives and false positives.

If you use them according to the instructions, you should not get false
negatives.

The reality is it does happen.

If you are using it right, it won't happen. i.e. If you have proven it
lights on a known good circuit, and does not light on a known dead one,
and nothing else has changed, then it will light for the live test circuit.

I've explained why.

Actually you haven't that I can see, although you have made the
assertion several times.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/12/2017 11:25, Harry Bloomfield wrote:
Robin expressed precisely :
I'd be more impressed by your confidence if you'd bothered to state
what you are taking to be the purpose of a volt stick. (Note I never
said I approved the use of a volt stick to prove a conductor "dead".
I do continue to fail to see why you claim they are "always unsound in
principle" to identify a live conductor - eg when there are several
conductors in a conduit.)

Volt sticks can vary in quality, Fluke sells one of the better ones. If
there are multiple live wires around it is possible your test wire might
show as being live - the simple solution is to shield the stick from all
but the wire you are interested in with your fingers. The validity then
needs to be crossed checked with something which actually draws some
current from the source. A test lamp works well for this.

I have never known a Fluke show a circuit as being dead, when it is
live, but the stick should always be tested before use. One test is to
rub the tip of the stick up and down your arm, whereupon it should light
up. They are absolutely great for non-invasive tests, but only if you
are practised in using one.

+1

And preferable to making physical connection to a circuit under test.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/12/2017 15:12, John Rumm wrote:
On 04/12/2017 11:25, Harry Bloomfield wrote:
Robin expressed precisely :
I'd be more impressed by your confidence if you'd bothered to state
what you are taking to be the purpose of a volt stick. (Note I never
said I approved the use of a* volt stick to prove a conductor "dead".
I do continue to fail to see why you claim they are "always unsound in
principle" to identify a live conductor - eg when there are several
conductors in a conduit.)

Volt sticks can vary in quality, Fluke sells one of the better ones. If
there are multiple live wires around it is possible your test wire might
show as being live - the simple solution is to shield the stick from all
but the wire you are interested in with your fingers.

Yes - and I had in mind in particular the way a volt stick then makes it
easy to check you've got the right one by turning on and off the circuit
you want.

I have never known a Fluke show a circuit as being dead, when it is
live, but the stick should always be tested before use. One test is to
rub the tip of the stick up and down your arm, whereupon it should light
up. They are absolutely great for non-invasive tests, but only if you
are practised in using one.

+1

And preferable to making physical connection to a circuit under test.


I don't know who makes the ones I've seen used to check 11kV overhead
lines are dead but think they are probably considered to be pretty
reliable too

--
Robin
reply-to address is (intended to be) valid

newshound brought next idea :
The false positive sounds like it might result from inductive coupling with
a parallel circuit. You sometimes see this with neon screwdrivers and DVMs,
although I've never seen it with a "volt stick".

Correct -if a wire with no connections at either end, is adjacent to
another live cable, the first can pickup from the second, causing the
stick to light up. If there is some sort of load remaining on the first
cable, then that will not happen because it is effectively grounded via
the load.

Brian Gaff submitted this idea :
Most of these only have one connection, a bit like the old fashioned Neon
Screwdriver. I'd really like one that makes a sound myself of course.

The neon drivers needed two, the tip to the cable, the metal top to
you. They depended on you having reasonable path the ground, which
wasn't always easy to achieve at the top of an insulated ladder.

A volt stick needs no ground, they work on the difference in field over
the length of the stick.

On Monday, 4 December 2017 13:59:10 UTC, Robin wrote:
On 04/12/2017 13:42, wrote:
On Monday, 4 December 2017 13:22:00 UTC, Robin wrote:
On 04/12/2017 12:59, tabbypurr wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent faults?

No, but it does require me to plonk people that lack expertise yet keep arguing.



Then why not tell me a volt meter which is incapable of giving a false
negative and prove me wrong?

An old smilie[1] meter would be good, provided you understood how to use it.




[1] AVO

On 04/12/2017 16:28, whisky-dave wrote:
On Monday, 4 December 2017 13:59:10 UTC, Robin wrote:
On 04/12/2017 13:42, wrote:
On Monday, 4 December 2017 13:22:00 UTC, Robin wrote:
On 04/12/2017 12:59, tabbypurr wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent faults?

No, but it does require me to plonk people that lack expertise yet keep arguing.



Then why not tell me a volt meter which is incapable of giving a false
negative and prove me wrong?

An old smilie[1] meter would be good, provided you understood how to use it.


I can see how that avoids false positives but not how it guarantees no
false negatives: I used an AVO in 1973-4 which had an intermittent "I
see nothing" fault (until the workshop resoldered a couple of joints).

--
Robin
reply-to address is (intended to be) valid

On Monday, 4 December 2017 15:40:18 UTC, Robin wrote:
On 04/12/2017 15:12, John Rumm wrote:
On 04/12/2017 11:25, Harry Bloomfield wrote:
Robin expressed precisely :
I'd be more impressed by your confidence if you'd bothered to state
what you are taking to be the purpose of a volt stick. (Note I never
said I approved the use of aÂ* volt stick to prove a conductor "dead".
I do continue to fail to see why you claim they are "always unsound in
principle" to identify a live conductor - eg when there are several
conductors in a conduit.)

Volt sticks can vary in quality, Fluke sells one of the better ones. If
there are multiple live wires around it is possible your test wire might
show as being live - the simple solution is to shield the stick from all
but the wire you are interested in with your fingers.

Yes - and I had in mind in particular the way a volt stick then makes it
easy to check you've got the right one by turning on and off the circuit
you want.

I have never known a Fluke show a circuit as being dead, when it is
live, but the stick should always be tested before use. One test is to
rub the tip of the stick up and down your arm, whereupon it should light
up. They are absolutely great for non-invasive tests, but only if you
are practised in using one.

+1

And preferable to making physical connection to a circuit under test.


I don't know who makes the ones I've seen used to check 11kV overhead
lines are dead but think they are probably considered to be pretty
reliable too

If you understand the limitations and follow correct procedure they are. That's very easy when trained & probing 11kV lines. It can sometimes fail to happen when Joe public uses them to check household wiring.


NT

On Monday, 4 December 2017 17:23:50 UTC, Robin wrote:
On 04/12/2017 16:28, whisky-dave wrote:
On Monday, 4 December 2017 13:59:10 UTC, Robin wrote:
On 04/12/2017 13:42, tabbypurr wrote:
On Monday, 4 December 2017 13:22:00 UTC, Robin wrote:
On 04/12/2017 12:59, tabbypurr wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very rare
indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent faults?

No, but it does require me to plonk people that lack expertise yet keep arguing.



Then why not tell me a volt meter which is incapable of giving a false
negative and prove me wrong?

An old smilie[1] meter would be good, provided you understood how to use it.


I can see how that avoids false positives but not how it guarantees no
false negatives: I used an AVO in 1973-4 which had an intermittent "I
see nothing" fault (until the workshop resoldered a couple of joints).

Nothing guarantees zero false negatives, equipment failures, operator errors & failure to follow safe procedures all occur. But voltage detectors that reference to the hand have the additional inbuilt screwup mode already described.


NT

On Mon, 04 Dec 2017 08:28:15 -0800, whisky-dave wrote:

On Monday, 4 December 2017 13:59:10 UTC, Robin wrote:
On 04/12/2017 13:42, wrote:
On Monday, 4 December 2017 13:22:00 UTC, Robin wrote:
On 04/12/2017 12:59, tabbypurr wrote:
On Monday, 4 December 2017 11:01:34 UTC, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:

you could always read up on how they work and why they give false
negatives and false positives.


And what's that got to do with the *principle* of capacitive
voltage sensing?

Do you understand that any volt meter is capable of giving a false
negative? With a good quality one used properly they will be very
rare indeed but not impossible.

wrong again.
As I said...


Does your faith require you to deny the existence of intermittent
faults?

No, but it does require me to plonk people that lack expertise yet
keep arguing.



Then why not tell me a volt meter which is incapable of giving a false
negative and prove me wrong?

An old smilie[1] meter would be good, provided you understood how to use
it.




[1] AVO

I have two!



--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On Mon, 04 Dec 2017 10:13:13 +0000, Andy Burns wrote:


The whole point of a non-contact mains detector is that it has zero
connections.

Like any tool they're fallible, they can give false negatives (e.g. for
live SWA cable) and false positives (e.g. for a USB cable) but they're
better than using your tongue.

Some do have audible output.

I believe the surest way is just to stick your finger in there. That
method never lets me down. But I would not suggest other people do that;
I have a higher skin resistance than most folk. 240V for me starts as a
slight tingle and builds up slowly. Takes about 5 seconds before it
becomes intolerable, presumably due to skin pores releasing moisture that
is then trapped and so increases conductivity.



--
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GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

On 04/12/2017 11:01, Robin wrote:
On 03/12/2017 23:08, wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:
On 03/12/2017 18:06, tabbypurr wrote:
On Sunday, 3 December 2017 17:41:40 UTC, Robin wrote:
On 03/12/2017 17:28, tabbypurr wrote:

They use an unsound principle and cannot be relied on. Don't buy

I'd be interested to learn more about that.

they produce false positives and false negatives, relying on one
is a hazard


I'm well aware of the possibility of a false negative with them (as
with
any device I've ever used). But I don't see why that makes the
*principle* of capacitive voltage sensing unsound.

it makes the way that principle is always applied unsound.

As for false positives, I take it you mean the way they will detect
voltages which are totally safe for human contact. On the whole I
prefer to see that not so much a false positive as an indication of
the
need to check further.

it isn't, it's just false positives. Come back when you understand
them.


I'd be more impressed by your confidence if you'd bothered to state what
you are taking to be the purpose of a volt stick.

to detect voltage?

(Note I never said I
approved the use of a volt stick to prove a conductor "dead". I do
continue to fail to see why you claim they are "always unsound in
principle" to identify a live conductor - eg when there are several
conductors in a conduit.)

you could always read up on how they work and why they give false
negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Its also interesting to note that many of the makers instruction sets
allude to the possibility of non detection due to a lack of reliable
ground reference (which they suggest is provided by the user). However
experiments demonstrate that the technology is somewhat more
sophisticated than that anyway since they function reliably even when
nowhere near an operator (or any other significant source of free
electrons (i.e. earth)).

If you look at the sequence of photos of the Fluke LVD2 in operation:

http://wiki.diyfaq.org.uk/index.php/...tion#Test_gear

It is able to detect the presence of a live wire even while sat on an
insulating bench and not obviously coupled to any ground reference.

I tried a similar experiment with my Fluke 1AC-II VoltAlert and got the
same result

https://www.amazon.co.uk/Fluke-1AC-I...s=fluke+1ac-ii



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/12/2017 23:19, Cursitor Doom wrote:
On Mon, 04 Dec 2017 10:13:13 +0000, Andy Burns wrote:


The whole point of a non-contact mains detector is that it has zero
connections.

Like any tool they're fallible, they can give false negatives (e.g. for
live SWA cable) and false positives (e.g. for a USB cable) but they're
better than using your tongue.

Some do have audible output.

I believe the surest way is just to stick your finger in there. That
method never lets me down. But I would not suggest other people do that;
I have a higher skin resistance than most folk. 240V for me starts as a
slight tingle and builds up slowly. Takes about 5 seconds before it
becomes intolerable, presumably due to skin pores releasing moisture that
is then trapped and so increases conductivity.



That reminds me of a teacher I had in about 1964. I took an old wind-up
generator (from a telephone) to school and had horseshoes of kids
holding hands with the ones on the ends holding wires - much hilarity
when I wound the handle. When I tried it on the teachers he showed no
effect so explained about skin resistance and demonstrated his ability
to a class of 10-11 year old boys by putting wires into a mains socket
and touching them both. There was no "don't try this at home" warning. A
stupid thing to do, but we were suitably impressed.

On 05/12/2017 12:46, John Rumm wrote:


And what's that got to do with the *principle* of capacitive voltage
sensing?

Its also interesting to note that many of the makers instruction sets
allude to the possibility of non detection due to a lack of reliable
ground reference (which they suggest is provided by the user). However
experiments demonstrate that the technology is somewhat more
sophisticated than that anyway since they function reliably even when
nowhere near an operator (or any other significant source of free
electrons (i.e. earth)).

If you look at the sequence of photos of the Fluke LVD2 in operation:

http://wiki.diyfaq.org.uk/index.php/...tion#Test_gear

It is able to detect the presence of a live wire even while sat on an
insulating bench and not obviously coupled to any ground reference.

I tried a similar experiment with my Fluke 1AC-II VoltAlert and got the
same result
Interesting. And I find my cheap LAP (much like the OP's) behaves
similarly - but is *much* less sensitive than the one in the Wiki photos
(or I'd wager your Fluke).

I suppose one explanation is that you have discovered homeopathic
coupling, where he volt stick remembers the capacitance from when it was
last held. Could be an opportunity to ensure your name liveth for
evermore in references such as "that's a Rumm effect".

--
Robin
reply-to address is (intended to be) valid

On Tuesday, 5 December 2017 12:46:28 UTC, John Rumm wrote:
On 04/12/2017 11:01, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:
On 03/12/2017 18:06, tabbypurr wrote:
On Sunday, 3 December 2017 17:41:40 UTC, Robin wrote:
On 03/12/2017 17:28, tabbypurr wrote:

They use an unsound principle and cannot be relied on. Don't buy

I'd be interested to learn more about that.

they produce false positives and false negatives, relying on one
is a hazard


I'm well aware of the possibility of a false negative with them (as
with
any device I've ever used). But I don't see why that makes the
*principle* of capacitive voltage sensing unsound.

it makes the way that principle is always applied unsound.

As for false positives, I take it you mean the way they will detect
voltages which are totally safe for human contact. On the whole I
prefer to see that not so much a false positive as an indication of
the
need to check further.

it isn't, it's just false positives. Come back when you understand
them.


I'd be more impressed by your confidence if you'd bothered to state what
you are taking to be the purpose of a volt stick.

to detect voltage?

(Note I never said I
approved the use of a volt stick to prove a conductor "dead". I do
continue to fail to see why you claim they are "always unsound in
principle" to identify a live conductor - eg when there are several
conductors in a conduit.)

you could always read up on how they work and why they give false
negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Its also interesting to note that many of the makers instruction sets
allude to the possibility of non detection due to a lack of reliable
ground reference (which they suggest is provided by the user). However
experiments demonstrate that the technology is somewhat more
sophisticated than that anyway since they function reliably even when
nowhere near an operator (or any other significant source of free
electrons (i.e. earth)).

If you look at the sequence of photos of the Fluke LVD2 in operation:

http://wiki.diyfaq.org.uk/index.php/...tion#Test_gear

It is able to detect the presence of a live wire even while sat on an
insulating bench and not obviously coupled to any ground reference.

I tried a similar experiment with my Fluke 1AC-II VoltAlert and got the
same result

https://www.amazon.co.uk/Fluke-1AC-I...s=fluke+1ac-ii

of course they are. Now hold them with some sort of hand coupled to a live conductor and they'll give inverted readings. The physics/electronics behind it is quite basic.


NT

On 03/12/2017 18:42, Mr Pounder Esquire wrote:
wrote:
On Sunday, 3 December 2017 17:41:40 UTC, Robin wrote:
On 03/12/2017 17:28, tabbypurr wrote:

They use an unsound principle and cannot be relied on. Don't buy

I'd be interested to learn more about that.

they produce false positives and false negatives, relying on one is
a hazard


I'm well aware of the possibility of a false negative with them (as
with any device I've ever used). But I don't see why that makes the
*principle* of capacitive voltage sensing unsound.

it makes the way that principle is always applied unsound.

As for false positives, I take it you mean the way they will detect
voltages which are totally safe for human contact. On the whole I
prefer to see that not so much a false positive as an indication of
the need to check further.

it isn't, it's just false positives. Come back when you understand
them.

Years ago I was given one of those gadgets. It was dead posh and detected
voltage in the walls where I knew there were wires.
Then it tried to tell me that there was voltage in the lounge door!
I recently bought a volt stick to detect voltage should I have a broken wire
in the vac cleaner etc. That is about they are good for.



I find that they are pretty useless on some flexes.

Still, they have their uses.

--
Adam

On 05/12/2017 16:31, wrote:

of course they are. Now hold them with some sort of hand coupled to a live conductor and they'll give inverted readings. The physics/electronics behind it is quite basic.

Take a 230V fluorescent task light in one hand (must check to see if its
double insulated), a Fluke volts stick in the other and the Fluke says
everything is live when it gets near to an earth!



--
Adam

On 05/12/2017 16:31, wrote:
On Tuesday, 5 December 2017 12:46:28 UTC, John Rumm wrote:
On 04/12/2017 11:01, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:
On 03/12/2017 18:06, tabbypurr wrote:
On Sunday, 3 December 2017 17:41:40 UTC, Robin wrote:
On 03/12/2017 17:28, tabbypurr wrote:

They use an unsound principle and cannot be relied on. Don't buy

I'd be interested to learn more about that.

they produce false positives and false negatives, relying on one
is a hazard


I'm well aware of the possibility of a false negative with them (as
with
any device I've ever used). But I don't see why that makes the
*principle* of capacitive voltage sensing unsound.

it makes the way that principle is always applied unsound.

As for false positives, I take it you mean the way they will detect
voltages which are totally safe for human contact. On the whole I
prefer to see that not so much a false positive as an indication of
the
need to check further.

it isn't, it's just false positives. Come back when you understand
them.


I'd be more impressed by your confidence if you'd bothered to state what
you are taking to be the purpose of a volt stick.

to detect voltage?

(Note I never said I
approved the use of a volt stick to prove a conductor "dead". I do
continue to fail to see why you claim they are "always unsound in
principle" to identify a live conductor - eg when there are several
conductors in a conduit.)

you could always read up on how they work and why they give false
negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Its also interesting to note that many of the makers instruction sets
allude to the possibility of non detection due to a lack of reliable
ground reference (which they suggest is provided by the user). However
experiments demonstrate that the technology is somewhat more
sophisticated than that anyway since they function reliably even when
nowhere near an operator (or any other significant source of free
electrons (i.e. earth)).

If you look at the sequence of photos of the Fluke LVD2 in operation:

http://wiki.diyfaq.org.uk/index.php/...tion#Test_gear

It is able to detect the presence of a live wire even while sat on an
insulating bench and not obviously coupled to any ground reference.

I tried a similar experiment with my Fluke 1AC-II VoltAlert and got the
same result

https://www.amazon.co.uk/Fluke-1AC-I...s=fluke+1ac-ii

of course they are. Now hold them with some sort of hand coupled to a live conductor and they'll give inverted readings.

Again never seen any evidence of that.

Could you suggest a test scenario that you think will fool it?

The physics/electronics behind it is quite basic.

Which by rights would suggest you could make some accurate predictions
based on the theory. So far it seems my Fluke has you outwitted at every
turn! ;-)




--
Cheers,

John.

/================================================== ===============\
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\================================================= ================/

On 05/12/2017 18:44, ARW wrote:
On 05/12/2017 16:31, wrote:

of course they are. Now hold them with some sort of hand coupled to a
live conductor and they'll give inverted readings. The
physics/electronics behind it is quite basic.

Take a 230V fluorescent task light in one hand (must check to see if its
double insulated), a Fluke volts stick in the other and the Fluke says
everything is live when it gets near to an earth!

The nearest equivalent I have been able to reproduce is to get one to
light on proximity to an earth or neutral when the operator is coupled
to live. However mine still reliably detects live as well in that
circumstance. If I can couple the butt end of the stick well enough to
live (i.e. wrapping an individual live wire round its handle), then it
just lights up and says "live" even if sat isolation on an insulating
surface. So far I have only been able to get a false positive, but not a
false negative...



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 05/12/2017 19:31, John Rumm wrote:
On 05/12/2017 18:44, ARW wrote:
On 05/12/2017 16:31, wrote:

of course they are. Now hold them with some sort of hand coupled to a
live conductor and they'll give inverted readings. The
physics/electronics behind it is quite basic.

Take a 230V fluorescent task light in one hand (must check to see if its
double insulated), a Fluke volts stick in the other and the Fluke says
everything is live when it gets near to an earth!

The nearest equivalent I have been able to reproduce is to get one to
light on proximity to an earth or neutral when the operator is coupled
to live. However mine still reliably detects live as well in that
circumstance. If I can couple the butt end of the stick well enough to
live (i.e. wrapping an individual live wire round its handle), then it
just lights up and says "live" even if sat isolation on an insulating
surface. So far I have only been able to get a false positive, but not a
false negative...



Adam mentioned his (I think) Fluke doesn't cope well with all flex; and
my cheap LAP is definitely capable of giving a flase negative on some
stuff unless I place it at the right angle.

I think false negatives were easier before they built in a "low battery"
signal

--
Robin
reply-to address is (intended to be) valid

On 05/12/2017 20:48, Robin wrote:
On 05/12/2017 19:31, John Rumm wrote:
On 05/12/2017 18:44, ARW wrote:
On 05/12/2017 16:31, wrote:

of course they are. Now hold them with some sort of hand coupled to a
live conductor and they'll give inverted readings. The
physics/electronics behind it is quite basic.

Take a 230V fluorescent task light in one hand (must check to see if its
double insulated), a Fluke volts stick in the other and the Fluke says
everything is live when it gets near to an earth!

The nearest equivalent I have been able to reproduce is to get one to
light on proximity to an earth or neutral when the operator is coupled
to live. However mine still reliably detects live as well in that
circumstance. If I can couple the butt end of the stick well enough to
live (i.e. wrapping an individual live wire round its handle), then it
just lights up and says "live" even if sat isolation on an insulating
surface. So far I have only been able to get a false positive, but not
a false negative...



Adam mentioned his (I think) Fluke doesn't cope well with all flex; and
my cheap LAP is definitely capable of giving a flase negative on some
stuff unless I place it at the right angle.

I think false negatives were easier before they built in a "low battery"
signal

My Fluke does a double flash of its light every two secs to show its
"working" - so should be harder to get caught by either it being off or
having a flat battery.

Here are the results of some experiments I did earlier tonight:

http://wiki.diyfaq.org.uk/index.php/...ck_experiments


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tuesday, 5 December 2017 18:44:08 UTC, John Rumm wrote:
On 05/12/2017 16:31, tabbypurr wrote:
On Tuesday, 5 December 2017 12:46:28 UTC, John Rumm wrote:
On 04/12/2017 11:01, Robin wrote:
On 03/12/2017 23:08, tabbypurr wrote:
On Sunday, 3 December 2017 21:35:32 UTC, Robin wrote:
On 03/12/2017 18:06, tabbypurr wrote:
On Sunday, 3 December 2017 17:41:40 UTC, Robin wrote:
On 03/12/2017 17:28, tabbypurr wrote:

They use an unsound principle and cannot be relied on. Don't buy

I'd be interested to learn more about that.

they produce false positives and false negatives, relying on one
is a hazard


I'm well aware of the possibility of a false negative with them (as
with
any device I've ever used). But I don't see why that makes the
*principle* of capacitive voltage sensing unsound.

it makes the way that principle is always applied unsound.

As for false positives, I take it you mean the way they will detect
voltages which are totally safe for human contact. On the whole I
prefer to see that not so much a false positive as an indication of
the
need to check further.

it isn't, it's just false positives. Come back when you understand
them.


I'd be more impressed by your confidence if you'd bothered to state what
you are taking to be the purpose of a volt stick.

to detect voltage?

(Note I never said I
approved the use of a volt stick to prove a conductor "dead". I do
continue to fail to see why you claim they are "always unsound in
principle" to identify a live conductor - eg when there are several
conductors in a conduit.)

you could always read up on how they work and why they give false
negatives and false positives.


And what's that got to do with the *principle* of capacitive voltage
sensing?

Its also interesting to note that many of the makers instruction sets
allude to the possibility of non detection due to a lack of reliable
ground reference (which they suggest is provided by the user). However
experiments demonstrate that the technology is somewhat more
sophisticated than that anyway since they function reliably even when
nowhere near an operator (or any other significant source of free
electrons (i.e. earth)).

If you look at the sequence of photos of the Fluke LVD2 in operation:

http://wiki.diyfaq.org.uk/index.php/...tion#Test_gear

It is able to detect the presence of a live wire even while sat on an
insulating bench and not obviously coupled to any ground reference.

I tried a similar experiment with my Fluke 1AC-II VoltAlert and got the
same result

https://www.amazon.co.uk/Fluke-1AC-I...s=fluke+1ac-ii

of course they are. Now hold them with some sort of hand coupled to a live conductor and they'll give inverted readings.

Again never seen any evidence of that.

Could you suggest a test scenario that you think will fool it?

The physics/electronics behind it is quite basic.

Which by rights would suggest you could make some accurate predictions
based on the theory. So far it seems my Fluke has you outwitted at every
turn! ;-)

I don't know why you're being silly. The cause of the problem is simple, well known, and I described it upthread. Nothing you've done has even begun to contradict what I said.


NT

On Tuesday, 5 December 2017 23:28:19 UTC, John Rumm wrote:

Here are the results of some experiments I did earlier tonight:

http://wiki.diyfaq.org.uk/index.php/...ck_experiments

In situations where the operator is well isolated from earth, this circuit can't be completed, and hence the neon may not illuminate even when connected to a live test point.

the circuit is completed via the stray capacitance of the human.


I would guess there is some quite clever electrical field gradient detection going on here and not a simple capacitively coupled potential divider.

I would first ask what the values of C were for live to human and human to ground.


NT

On Tue, 05 Dec 2017 13:49:00 +0000, bin wrote:

That reminds me of a teacher I had in about 1964. I took an old wind-up
generator (from a telephone) to school and had horseshoes of kids
holding hands with the ones on the ends holding wires - much hilarity
when I wound the handle. When I tried it on the teachers he showed no
effect so explained about skin resistance and demonstrated his ability
to a class of 10-11 year old boys by putting wires into a mains socket
and touching them both. There was no "don't try this at home" warning. A
stupid thing to do, but we were suitably impressed.

Yup. And 10 years later the teacher *would* say, "don't try this at home."
Fast forward to 2017 and just recounting the story with the caveat would
probably end that teacher's career. We live in excessively safety-
conscious times. A 'good' war would soon sort that out for a few
generations.



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protocols constitutes acceptance of this condition.

On 05/12/2017 23:51, wrote:
On Tuesday, 5 December 2017 23:28:19 UTC, John Rumm wrote:

Here are the results of some experiments I did earlier tonight:

http://wiki.diyfaq.org.uk/index.php/...ck_experiments

In situations where the operator is well isolated from earth, this circuit can't be completed, and hence the neon may not illuminate even when connected to a live test point.

the circuit is completed via the stray capacitance of the human.


I would guess there is some quite clever electrical field gradient detection going on here and not a simple capacitively coupled potential divider.

I would first ask what the values of C were for live to human and human to ground.

You can eliminate the human since the detector works in isolation - even
if the human walks to the other side of the room.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 05/12/2017 23:45, wrote:
On Tuesday, 5 December 2017 18:44:08 UTC, John Rumm wrote:
On 05/12/2017 16:31, tabbypurr wrote:


The physics/electronics behind it is quite basic.

Which by rights would suggest you could make some accurate predictions
based on the theory. So far it seems my Fluke has you outwitted at every
turn! ;-)

I don't know why you're being silly. The cause of the problem is simple, well known, and I described it upthread. Nothing you've done has even begun to contradict what I said.

Must have missed it then. What did you say upthread?


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Cursitor Doom wrote:

On Tue, 05 Dec 2017 13:49:00 +0000, bin wrote:

That reminds me of a teacher I had in about 1964. I took an old wind-up
generator (from a telephone) to school and had horseshoes of kids
holding hands with the ones on the ends holding wires - much hilarity
when I wound the handle. When I tried it on the teachers he showed no
effect so explained about skin resistance and demonstrated his ability
to a class of 10-11 year old boys by putting wires into a mains socket
and touching them both. There was no "don't try this at home" warning. A
stupid thing to do, but we were suitably impressed.

Yup. And 10 years later the teacher *would* say, "don't try this at home."
Fast forward to 2017 and just recounting the story with the caveat would
probably end that teacher's career. We live in excessively safety-
conscious times. A 'good' war would soon sort that out for a few
generations.

I share your distaste for the excessive safety consciousness, and the
restriction of children's 'right to roam'. But the fact is that
illness and even accident kill very few children now, and a risk that
would be lost in the noise 80 years ago is a doubling of mortality now.
Thus safety culture saves much heartache and misery.

We may not like it, but it is probably a worthwhile thing.


--

Roger Hayter

"Cursitor Doom" wrote in message
news
On Tue, 05 Dec 2017 13:49:00 +0000, bin wrote:

That reminds me of a teacher I had in about 1964. I took an old wind-up
generator (from a telephone) to school and had horseshoes of kids
holding hands with the ones on the ends holding wires - much hilarity
when I wound the handle. When I tried it on the teachers he showed no
effect so explained about skin resistance and demonstrated his ability
to a class of 10-11 year old boys by putting wires into a mains socket
and touching them both. There was no "don't try this at home" warning. A
stupid thing to do, but we were suitably impressed.

Yup. And 10 years later the teacher *would* say, "don't try this at home."
Fast forward to 2017 and just recounting the story with the caveat would
probably end that teacher's career. We live in excessively safety-
conscious times.

A 'good' war would soon sort that out for a few generations.

Odd that it didnt with the last world war.

In article ,
says...


Correct -if a wire with no connections at either end, is adjacent to
another live cable, the first can pickup from the second, causing the
stick to light up. If there is some sort of load remaining on the first
cable, then that will not happen because it is effectively grounded via
the load.


Not long after I started work - so the best part of 60 years
ago - I recall getting a belt off a loudspeaker cable. It
was in an old working man's club (it was demolished soon
after and replaced by a modern building) so I've no idea how
old it was.

The walls and extremely high ceilings were all clad in wood
and, as far as we could ascertain, the wiring ran up the
wall behind the cladding and across the ceiling of a large
hall then across the ceiling of an adjacent large room and
down the wall to where the remote speaker was sited.

We actually measured close to the full mains voltage on this
cable with an AVO 8! I can only assume that the mains wiring
consisted of physically separate conductors and that the
speaker wiring was run alongside for its considerable
length.

I'm not sure now how we proved that this was purely induced
and not dangerous and fortunately, the amplifier to which it
was connected was earthed - not always the case with such
ancient wiring, of course - otherwise using the microphone
could have been quite 'entertaining'!

--

Terry

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