screwdriver tester

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

 

[Jamie]

pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

It's magic dust!

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[John Popelish]

pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

Even with no ground connection to complete a resistive
circuit, your body has capacitance to the rest of the
universe, so charges and discharges each half cycle of the
AC with a small capacitive current. This small capacitive
current (sub milliampere) is well below your threshold of
feeling, but is above the threshold to light a small neon bulb.

If the AC voltage were much higher (say, hundreds of
thousands of volts, like what is carried on the high voltage
transmission lines that cross the continent) the capacitive
currents they would drive into your body capacitance would
reach the threshold of feeling, even if you were suspended
from a helicopter.

 

[Stephen J. Rush]

On Mon, 08 Oct 2007 11:04:08 -0400, Jamie wrote:

pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

It's magic dust!

That, plus the very low (< .1 ma) current required by a small neon lamp,
plus the unipolar capacitance of your body. The tester has a large
resistance in series with the lamp, so you won't get stung even if you are
grounded.

 

[Eeyore]

pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

Graham

 

[Jamie]

Eeyore wrote:

pratikgetz@gmail.com wrote:


when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?


You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

Graham


really, I thought it had something to do with capacitance with

AC combined.
Oh well, back to school.
snort snort..


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Eeyore]

Jamie wrote:

Eeyore wrote:
pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?


You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

really, I thought it had something to do with capacitance with
AC combined.
Oh well, back to school.
snort snort..

Are you saying that the body (or wood) is incapable of making a resistive connection ?

Graham

 

[John Fields]

On Mon, 08 Oct 2007 16:19:00 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

---
Sorry, Bozo, it's capacitance.


--
JF

 

[Michael A. Terrell]

Eeyore wrote:

Jamie wrote:

Eeyore wrote:
pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?


You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

really, I thought it had something to do with capacitance with
AC combined.
Oh well, back to school.
snort snort..

Are you saying that the body (or wood) is incapable of making a resistive connection ?

Your body is one plate of a capacitor, and the earth is the other
plate. It has nothing to do with resistance, in this application. it
is like running your hand along the glass of a fluorescent lap that
doesn't come on when you apply power.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Rich Grise]

On Mon, 08 Oct 2007 17:15:00 +0100, Eeyore wrote:

Jamie wrote:
Eeyore wrote:
pratikgetz@gmail.com wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?


You're acting as a large value resistor. Enough current passes to
light the neon bulb without giving you a shock.

really, I thought it had something to do with capacitance with AC
combined.
Oh well, back to school.
snort snort..

Are you saying that the body (or wood) is incapable of making a resistive
connection ?

Not at all, merely that in this case the conductance is negligible
compared to the capacitive reactance.

Hope This Helps!
Rich

 

On Mon, 08 Oct 2007 16:19:00 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

Graham

If you placed one 60 hz 120v wire upstairs in a wooden house with no
other wiring or metal objects and the neon lamp still lit I would
guess that trickle energy and the wire voltage that made the neon bulb
light converted into trickle radiation into the air space surrounding
our candidate holding the other end of the wire.

I think radiation resistance through our candidate is as good an
answer as capacitance on our candidates skin to some earth grounding
surface ten feet away.

At higher frequencies possible, but 50/60 hz, I would need to ask
Radium.



Usenet was a wild frontier 10 years ago. I remember ;-)
Then Google invited itself to our campfire.

* * *
Christopher

Temecula CA.USA
http://www.oldtemecula.com

 

[sparky]

On Oct 8, 11:19 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

pratikg...@gmail.com wrote:
when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

Graham

The wood is an insulator. The current flows through you because of
capacitance.

 

[Jon Slaughter]

"craigm" <none@domain.invalid> wrote in message
news:FiBOi.73$ZK1.154755@news.sisna.com...

sparky wrote:

On Oct 8, 11:19 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:
pratikg...@gmail.com wrote:
when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

You're acting as a large value resistor. Enough current passes to light
the neon bulb without giving you a shock.

Graham

The wood is an insulator. The current flows through you because of
capacitance.

Depending upon the moisture content, wood may be a poor insulator.

So the screwdriver comes with a waterlogged wooden stool?

 

[zhafran]

On Oct 9, 9:45 am, sparky <sparky...@yahoo.com> wrote:

On Oct 8, 11:19 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:

pratikg...@gmail.com wrote:
when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire the
bulb lights up even while i am standing on the wooden stool how can a
bulb light without getting earthing?

You're acting as a large value resistor. Enough current passes to light the neon
bulb without giving you a shock.

Graham

The wood is an insulator. The current flows through you because of
capacitance.

A beginner question here:
Since it is due to capacitance, does it mean that the neon lamp will
be turned ON for only a few second when we're testing it with DC
voltage? Because capacitance has the characteristics to block DC when
it's fully charged right?

 

[John Popelish]

zhafran wrote:

A beginner question here:
Since it is due to capacitance, does it mean that the neon lamp will
be turned ON for only a few second when we're testing it with DC
voltage? Because capacitance has the characteristics to block DC when
it's fully charged right?

Yes. One flash, till you discharge the DC voltage on your
body and the plastic surfaces of the screw driver handle.
again.

But don't take my word for it. Series connect a stack of 12
each 9 volt transistor radio batteries, with one terminal
grounded. Touch the other terminal that with the screw
driver, and it should produce a single faint blink. Have
someone else reverse the end grounded and tough the other
end and you should get another blink.

 

[Rich Grise]

On Tue, 09 Oct 2007 16:55:04 -0700, zhafran wrote:

On Oct 9, 9:45 am, sparky <sparky...@yahoo.com> wrote:
On Oct 8, 11:19 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com
pratikg...@gmail.com wrote:
when i stand on a wooden stool and touch a live wire i dont get a
shock because circuit is not complete with ground as wood is a
insulator but when i touch a screwdriver tester to that live wire
the bulb lights up even while i am standing on the wooden stool how
can a bulb light without getting earthing?

You're acting as a large value resistor. Enough current passes to
light the neon bulb without giving you a shock.

The wood is an insulator. The current flows through you because of
capacitance.

A beginner question here:
Since it is due to capacitance, does it mean that the neon lamp will be
turned ON for only a few second when we're testing it with DC voltage?
Because capacitance has the characteristics to block DC when it's fully
charged right?

That would be true if you were testing a DC circuit. Usually, those
things are used on AC mains, and it's that AC that flows through
the capacitive reactance of your body capacitance to ground. It's
not much current (probably way less than one mA), but neon bulbs don't
need much.

Hope This Helps!
Rich

 

[Rich Grise]

On Tue, 09 Oct 2007 20:04:21 -0400, John Popelish wrote:

zhafran wrote:

A beginner question here:
Since it is due to capacitance, does it mean that the neon lamp will be
turned ON for only a few second when we're testing it with DC voltage?
Because capacitance has the characteristics to block DC when it's fully
charged right?

Yes. One flash, till you discharge the DC voltage on your body and the
plastic surfaces of the screw driver handle. again.

But don't take my word for it. Series connect a stack of 12 each 9 volt
transistor radio batteries, with one terminal grounded. Touch the other
terminal that with the screw driver, and it should produce a single faint
blink. Have someone else reverse the end grounded and tough the other end
and you should get another blink.

zhafran, if you do this, use EXTREME CAUTION. 108 volts is enough to drive
lethal current through your skin. If you insist on doing this test, then
keep one hand in your pocket.

Good Luck!
Rich

 

[Nobody]

On Tue, 09 Oct 2007 16:55:04 -0700, zhafran wrote:

The wood is an insulator. The current flows through you because of
capacitance.

A beginner question here:
Since it is due to capacitance, does it mean that the neon lamp will
be turned ON for only a few second when we're testing it with DC
voltage?

More likely a few {micro,milli}seconds; the capacitance involved is a few
picofarads.

Because capacitance has the characteristics to block DC when
it's fully charged right?

Right.

 

[zhafran]

On Oct 11, 2:53 am, Rich Grise <r...@example.net> wrote:

On Tue, 09 Oct 2007 20:04:21 -0400, John Popelish wrote:
zhafran wrote:

A beginner question here:
Since it is due to capacitance, does it mean that the neon lamp will be
turned ON for only a few second when we're testing it with DC voltage?
Because capacitance has the characteristics to block DC when it's fully
charged right?

Yes. One flash, till you discharge the DC voltage on your body and the
plastic surfaces of the screw driver handle. again.

But don't take my word for it. Series connect a stack of 12 each 9 volt
transistor radio batteries, with one terminal grounded. Touch the other
terminal that with the screw driver, and it should produce a single faint
blink. Have someone else reverse the end grounded and tough the other end
and you should get another blink.

zhafran, if you do this, use EXTREME CAUTION. 108 volts is enough to drive
lethal current through your skin. If you insist on doing this test, then
keep one hand in your pocket.

Good Luck!
Rich

Does it also applicable to high AC voltage?

 

[Rich Grise]

On Wed, 10 Oct 2007 16:12:15 -0700, zhafran wrote:

On Oct 11, 2:53 am, Rich Grise <r...@example.net> wrote:
On Tue, 09 Oct 2007 20:04:21 -0400, John Popelish wrote:
zhafran wrote:

A beginner question here:
Since it is due to capacitance, does it mean that the neon lamp will be
turned ON for only a few second when we're testing it with DC voltage?
Because capacitance has the characteristics to block DC when it's fully
charged right?

Yes. One flash, till you discharge the DC voltage on your body and the
plastic surfaces of the screw driver handle. again.

But don't take my word for it. Series connect a stack of 12 each 9 volt
transistor radio batteries, with one terminal grounded. Touch the other
terminal that with the screw driver, and it should produce a single faint
blink. Have someone else reverse the end grounded and tough the other end
and you should get another blink.

zhafran, if you do this, use EXTREME CAUTION. 108 volts is enough to drive
lethal current through your skin. If you insist on doing this test, then
keep one hand in your pocket.

Does it also applicable to high AC voltage?

Yes; however, the "screwdriver tester" with the NE-2 bulb has an insulated
handle - the only current that can flow is through the bulb, and there's
probably a current-limiting resistor in series as well.

But, as long as you're only touching the plastic part, you'll be OK -
the reason for the safety warnings is becase if one hand is grounded,
or you're standing in water, and your hand slips and contacts the HV
AC, it can kill you.

The point is to not give the current any path through yourself, but
like I say, the little neon testers should be OK, if you're only
holding the plastic part.

Hope This Helps!
Rich