Unreliable voltage detector
Richard Evans
the size and shape of a magic marker, but instead of a felt tip it has
a flat blade with which to probe for live voltage. Stick it into a
receptacle or even touch it to the outside of a live cable and it
flashes and beeps. At least, it used to.
Last night, I applied it to a cable I was pretty sure was live and it
was mute. I then tried it in a receptacle I knew was hot and it was
still mute. I tested the batteries. They were good, but I replaced
them anyway. Still nothing. I then resigned myself to buying a new one
and tossed it into a box of batteries, where it immediately began
beeping. I took it out and started testing it again and it beeped
accurately, until I turned it off and back on, then nothing again.
So, the problem appears to be in the switch, though the thing is so
simple I don't know how it could be failing intermittently.
Bottom line: Once the thing is on and known to be working, it is
reliable until turned off. Once turned off, it has to be tested on a
known live circuit when it's turned on again. (Which is recommended
practice anyway.)
My concern now is: Once it's on and working, can I depend on it to
work for as long as it's on? Could it just stop working without
warning?
Unless someone has some simple solution, I guess I'm off to buy a new
one.
Bill
electricity or call a professional.
"Richard Evans" wrote in message
kcarl...@yahoo.com
I have one of those non-contact voltage detectors. Number 1 rule in
using it is to check it against a known live cicuit to confim that it
is working, then go test the circuit you need to (usually to make sure
all the wires in the box you want to work on are dead), and then go
retest against the known live circuit.
Ken
dpb
...
> My concern now is: Once it's on and working, can I depend on it to
> work for as long as it's on? Could it just stop working without
> warning?
>
> Unless someone has some simple solution, I guess I'm off to buy a new
> one.
Fluke has a model that has continuous self-test if you're in the market.
Unless can discover an intermittent connection at switch that is
repairable or some similar, seems like best solution. Being unsure of
reading is worse than no measurement and simply assuming everything is
live imo.
--
Ralph Mowery
"Bill" <billnoma...@yahoo.com> wrote in message
news:79a4igF...@mid.individual.net...
>I suggest you learn to use a multimeter if you are going to be working with
>electricity or call a professional.
>
Either that or a light bulb detector. Something that makes direct
connection to the wires. I work as an electrician in a large plant and we
were given detectors similar to that around 10 years ago (the company
furnishes all the tools). I never did trust the things. Especially not
enough to grab a wire. I carry one in my tool pouch, but seldom use it, I
usually use the Fluke t-100 meter I have. Guess that I am old school and
still like the Simpson 260, but I don't usually carry it as it is too big to
fit in my back pocket.
Ralph Mowery
<kcarl...@yahoo.com> wrote in message
news:f4a7e76a-cd57-4ab8...@21g2000vbk.googlegroups.com...
>On Jun 10, 12:02 pm, Richard Evans I have one of those non-contact voltage
using it is to check it against a known live cicuit to confim that it
is working, then go test the circuit you need to (usually to make sure
all the wires in the box you want to work on are dead), and then go
>retest against the known live circuit.
>Ken
That should be the # 1 rule always nomater what you use.
Smitty Two
Richard Evans <inf...@mindspring.com> wrote:
Yes, it quite readily could.
>
> Unless someone has some simple solution, I guess I'm off to buy a new
> one.
If it were mine, I'd take it apart and look for a cold or cracked solder
connection. Finding one I'd resolder it. Failing that I'd replace the
switch.
Charlie
"Richard Evans" <inf...@mindspring.com> wrote in message
news:kglv25hqd8t3t26n0...@4ax.com...
I just use a bug light. It used to be a neon pilot light. Entirely self
contained.
However, if you really want to use your toy detector, check the battery
contacts in the device. They should be clean and shiny and have lots of
spring so that you get a nice tight fit.
Charlie
AZ Nomad
>I suggest you learn to use a multimeter if you are going to be working with
>electricity or call a professional.
high impedance multimeters work very poorly on house wiring. The
capacitance between a pair of wires reads the same as a connection.
I've resorted to wiring a spare lamp socket as a test lamp to have a
low impedance "test light".
tra...@optonline.net
> "Richard Evans" <info...@mindspring.com> wrote in message
>
> - Show quoted text -
Since it's almost new, I'd contact the manufacturer. On many cheap
things like this, they just send you a new one. It may be under
warranty too. If that doesn't work, then I guess I'd take it apart
and do some investigating, but I sure wouldn't trust it unless you can
find and fix what ails it.
John Grabowski
"Richard Evans" <inf...@mindspring.com> wrote in message
news:kglv25hqd8t3t26n0...@4ax.com...
*I had a Greenlee and found it to be less than perfect. I now use a Fluke
and love it. No more false readings.
The Daring Dufas
My clamp-on amp meter has a detector built in.
I push the data hold button with it turned off
and the continuity beeper buzzes with AC hum.
It's very reliable.
TDD
HeyBub
Send it to Greenlee with a note:
"Thought you might like to investigate the failure mode on the enclosed
GT-11 with a view toward making a more reliable unit.
"I wouldn't say no to a replacement..."
They're a pretty good company - I'll give 8-to-5 you get a new probe.
Stormin Mormon
all that routine.
--
Christopher A. Young
Learn more about Jesus
www.lds.org
.
<kcarl...@yahoo.com> wrote in message
news:f4a7e76a-cd57-4ab8...@21g2000vbk.googlegroups.com...
Bob(but not THAT Bob)
I've had one of these for 30 yrs and I've always been able to trust it:
http://www.testitfirst.com/site/972962/product/TIF%20300HV
Of course, it was around 25 bucks back then
Red Green
news:4oKdne8PaI8eta3X...@earthlink.com:
....Although the shock I received was very uncomfortable, at least I
wasn't on a ladder, fell and got injured. Lawyers around here eat that
shit up.
Smitty Two
"Stormin Mormon" <cayoung61**spamblock##@hotmail.com> wrote:
> That doesn't save much time, or effort. Since you go through
> all that routine.
Nevertheless, the triple test Ken outlined is mandatory in most
institutional or industrial troubleshooting and repair departments.
Lockout / tagout is also required. It saves lives, particularly when you
get up above 220 volts.
Ralph Mowery
"Smitty Two" <prest...@earthlink.net> wrote in message
news:prestwhich-60FC4...@newsfarm.iad.highwinds-media.com...
That is right. It has nothing to do with saving time or effort. It is
about saving your ass.
David Combs
AZ Nomad <azno...@PremoveOBthisOX.COM> wrote:
>On Wed, 10 Jun 2009 09:16:03 -0700, Bill <billnoma...@yahoo.com> wrote:
>>I suggest you learn to use a multimeter if you are going to be working with
>>electricity or call a professional.
>
>high impedance multimeters work very poorly on house wiring. The
>capacitance between a pair of wires reads the same as a connection.
Maybe I'm wrong, but I thought those were the good ones? Probably am wrong.
Anyway, why are they no good for house wiring (as opposed to other things)?
Thanks!
David
Ralph Mowery
"David Combs" <dkc...@panix.com> wrote in message
news:h369sh$62a$3...@reader1.panix.com...
The high impedance voltmeters will pick up what may be referred to as
'phantom' or induced voltage. They require almost no current to read
voltage. A very small ammount of breakdown in the insulation of the wiring
will cause a wrong voltage to be shown. If two wires are close to each
other and one has power on it and the other one does not have any power, it
is possiable the high impedance meter will show a voltage due to the
capacitance or inductance between the wires. A low impedance meter that
takes some power to operate will not show the voltage or will show a very
much reduced voltage.
I would not recomend it, but I have a Fluke meter that costs around $ 300
and I can plug one lead into a socket and hold the other lead and read 115
volts. If it was really 115 volts at much current I could feel it. It only
requires about .001 to .003 amps to be felt on the outside of the skin. It
only takes .1 amps at 120 volts to light up a 12 watt lightbulb.
Digital meters should really be used in in electronic devices and the older
analog meters should be used around the house. Much easier for a person to
use that are not familiar with how the meters work.
AZ Nomad
The problem is the high impedance. Put a 200K resistor across the terminals
and then they'l work just fine. However, at high impedance, they'll measure a
wire running alongside a hot wire just like it was hot itself.
David Combs
Any suggestions on what to read to get a good understanding of
all this?
And, what words to search for on wikipedia?
Thanks!
David
AZ Nomad
ohm's law
Smitty Two
AZ Nomad <azno...@PremoveOBthisOX.COM> wrote:
>
> ohm's law
Damn, son, that's *exactly* what I was going to say. I mean, uh, type.
bud--
There is an explanation of "phantom voltage" at:
http://www.nema.org/stds/eng-bulletins/upload/Bulletin-88.pdf
It probably doesn't say much more than Ralph posted.
Digging out some old notes:
A good analog meter will have an input impedance (AC scales) of about
"5,000 ohms per volt". On a 150V scale the resistance of the meter will
be 750,000 ohms.
To read 120V, the current through the meter will be 0.00016A (160
microamps).
A digital meter will have a higher input impedance, say 10 megohms
(probably higher).
To read 120V, the current through the meter will be 0.000000012A (12
microamps).
This is a very small current.
===============
A couple years ago I measured the capacitance between 2 insulated
conductors in a 3 conductor with ground Romex as 15 pf per foot (other 2
conductors open).
For 20 feet that is 300pf.
At 60 Hz, the 20 feet of Romex will have capacitive reactance of 8.8 megohms
====================
With 20 ft of the Romex above, one Romex wire to hot, 2nd Romex wire to
digital meter and other digital meter lead to neutral you have the 8.8
megohm capacitive reactance is in series with 10 megohm meter. With 120V
across the 18.8 megohm total the meter reading is about 64 volts.
Actually that is wrong because the capacitive reactance and resistance
don't just add. If added correctly the total impedance is 13.3 megohms
and the meter reading is about 90 volts.
=====================
The 8.8 megohm capacitive reactance in series with a 750,000 ohm analog
meter will give a much smaller voltage because the capacitive reactance
is much higher than the meter resistance. The analog meter will read
about 10 volts.
The capacitive reactance is so much higher than the meter resistance,
the current is pretty constant if you switch to lower scales, and the
reading will stay about 6% of full scale. (This can be as odd as having
any voltage at all.)
========================
The example above would be similar to measuring the voltage at a light
bulb socket (no bulb) where there is a 20 ft run of old ungrounded Romex
to a light switch that is turned off. The run to the light switch has a
hot supply wire and the switched return wire. The capacitance between
the wires gives the meter reading.
=======================
All measuring devices have limitations. Knowing what the limitations are
is part of the challenge of making measurements. The digital meter
measures an actual voltage (and probably measures low). But the
"phantom" voltage has no practical significance.
--
bud--
blueman
> Digging out some old notes:
>
> A good analog meter will have an input impedance (AC scales) of about
> "5,000 ohms per volt". On a 150V scale the resistance of the meter
> will be 750,000 ohms.
>
> To read 120V, the current through the meter will be 0.00016A (160
> microamps).
>
>
> A digital meter will have a higher input impedance, say 10 megohms
> (probably higher).
>
> To read 120V, the current through the meter will be 0.000000012A (12
> microamps).
> This is a very small current.
When I was saving up presents to buy my first VOHM back when I was a
young kid in the earl-70s, all consumer versions were analog. In those
days, the more you paid the higher the input impedance -- because it
was useful for electronics (so that the measurement wouldn't affect
the reading) and since getting high input impedence was expensive back
then. I think there were some models (out of my price range) that had
megohm type input impedance using FETs but I the best I could afford
was one with about 20Kohm/volt.
Interesting that now the situation is reversed -- all the cheap
(Chinese-made) multimeters are digital with megohm input impedances
while you have to pay extra to get an "old-fashioned" analog one.
I think I recently saw my old Archer (Radio Shack) multimeter lying
around in a box at my parents' house. I probably should retrieve
it. By the way, I think I paid about $20 for it on-sale back in the
day which was a heck of a lot of money then for a 10 year old kid who
was getting 10 cents a week in allowance (and it wasn't the lowest end
one either).
bud--
The first meter I bought when I was a kid was a 20Kohns/volt Lafayette
kit. I suspect a bunch of us learned a lot of electronics from kits. I
don't know how kids learn electronics now.
The main alternative back then was a VTVM - thats a vacuum tube volt
meter for the younger types. I probably still have one of those around.
It always amazes me that the 20Kohm/volt meter movements are 50 micoamps
full scale. Hard to imagine you can make something that sensitive rugged
enough for field work.
Those meter are typically 5Kohms/volt on AC scales, which I used in my
calculations. If I remember right you need higher current to get the
diodes in a more linear operating area.
--
bud--
Paul
I threw mine in the trash after having it for ten years. I pulled it out to
use it and put fresh batteries in it after leaving it battery free for a year
and half the time it worked and half the time it doesn’t. Smash it with a
hammer and throw it in the trash. I got on a few forums with real life
electricians and they all had issues with all of these no touch voltage
detectors.
--
for full context, visit https://www.homeownershub.com/maintenance/unreliable-voltage-detector-377844-.htm
gfre...@aol.com
<caedfaa9ed1216d60ef...@example.com> wrote:
>replying to Richard Evans, Paul wrote:
>I threw mine in the trash after having it for ten years. I pulled it out to
>use it and put fresh batteries in it after leaving it battery free for a year
>and half the time it worked and half the time it doesn’t. Smash it with a
>hammer and throw it in the trash. I got on a few forums with real life
>electricians and they all had issues with all of these no touch voltage
>detectors.
in the drop bin at Northern Tools is junk.