Question about reversed-polarity in an AC outlet

[Jim Thompson]

One old boss used to test 240 VAC light sockets for live with his thumb!

N

My father, an electrician until he went into the TV repair business in
the early '50's, used to test 110VAC with two fingers. Scared the
hell out of me. But he's still alive, so who am I to criticize ;-)

...Jim Thompson

 

[Robert Monsen]

My father, an electrician until he went into the TV repair business in
the early '50's, used to test 110VAC with two fingers. Scared the
hell out of me. But he's still alive, so who am I to criticize ;-)

...Jim Thompson

Check out the last paragraph

http://www.fathom.com/course/21701713/session1.html

The Victorians just loved to shock each other. Literally.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Rich Grise]

Check out the last paragraph

http://www.fathom.com/course/21701713/session1.html

The Victorians just loved to shock each other. Literally.

I saw some guy in some electricity show, and one of the features was
his big Tesla coil - it was about 4' tall and about 18" in diameter,
and for the grand finale he stood on top of it and was throwing
coronas off his fingertips. He was kind of grimacing, as if he was
in pain but trying not to show it. It was probably pretty tingly!

Cheers!
Rich

 

[NSM]

I saw some guy in some electricity show, and one of the features was
his big Tesla coil - it was about 4' tall and about 18" in diameter,
and for the grand finale he stood on top of it and was throwing
coronas off his fingertips. He was kind of grimacing, as if he was
in pain but trying not to show it. It was probably pretty tingly!

There's some woman performer who shoots sparks out of her metal finger tips
(thimbles or similar) then does it with a tongue stud! (Seen on 'Believe It
Or Not').

N

 

[RonKZ650]

I knew a guy who would hold a 25KV high voltage lead in one hand, put
his finger in the anode of a color TV CRT and say "fire it up". Someone
else would plug the set in, and he'd light the screen up with 25K
running through his body. He said no shock could even be felt.
This being said, be careful of those faucets in your bathtub, may have
AC on them? How in the hell????

 

[Michael A. Terrell]

I knew a guy who would hold a 25KV high voltage lead in one hand, put
his finger in the anode of a color TV CRT and say "fire it up". Someone
else would plug the set in, and he'd light the screen up with 25K
running through his body. He said no shock could even be felt.
This being said, be careful of those faucets in your bathtub, may have
AC on them? How in the hell????

I worked in a TV shop while in Junior high school. An old tech there
would grab the HV lead to the CRT as he turned on the chassis, then
after they high voltage came up he would casually reach out and tap
someone on the shoulder, or elbow. I'm surprised no one ever decked him
for it. Lucky for me, my bench was ten feet away from his and he
couldn't reach me.

 

[Michael A. Terrell]

I'm gonna go out on a limb here. I'm guessing you're not supplying all the
relevant info or I'm confused. Straighten me out if necessary. I can
probably agrre with you if there is an isolation transformer in the picture
somewhere(i'm speaking of portable electrical equipment). The main fuse or
breaker will take care of the line voltage. The secondary will be protected
by a fuse. If the equipment has no transformer for a power supply, is there
a fuse protecting the equipment from the line voltage...sorry amperage? I
think you'd be hard pressed to find any equipment without one. True it's to
protect the circuitry of the equipment but you will find a fuse on the "HOT"
side.

There may be a fuse inside a piece of equipment, but not in the AC
plug in the US. If the fuse is in the plug some idiot can take a pair
of dykes and clip the wide part off a plug and reverse it. This would
leave the item hot when the fuse blows. By having the fuse on the
inside of the equipment they have to do more tampering. You can still
get hurt, but the idiot who gets hurt can't sue you because of his
stupidity. Most electrical rules and regs are written by insurance
boards. If you don't meet their standards, you don't get insurance, or
they can refuse to pay out after something happens when they can prove
someone didn't follow the rules.

Some cheap imported Christmas lights have very small fuses in the
plug because they have a link that arcs and shorts around blown bulbs.
After you lose enough bulbs you will get a chain reaction and have a
loop of wire across the plug. No fuse in this case would cause a fire
before the 15 or 20 amp circuit breaker could trip.

 

[Sam Goldwasser]

There's some woman performer who shoots sparks out of her metal finger tips
(thimbles or similar) then does it with a tongue stud! (Seen on 'Believe It
Or Not').

With a Tesla coil, the current is so low that it's all pretty harmless.
With any metal, then you probably don't feel much of anything. Just
like walking across a carpet and touching a door knob. You'll feel it
if the spark jumps from your finger, but not if you're holding a piece
of metal and it jumps from that. For the Tesla coil, you also have
the high frequency which means means the current stays on the surface
due to the skin effect.

I remember science museum demos something along the lines of they would
arrange a line of kids holding hands with the first one's free hand on
the Tesla coil sphere and the last one lighting a fluorsecent tube just
by holding it.

Not sure if they still do stuff like that with all the lawyers around.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
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[Sam Goldwasser]

I knew a guy who would hold a 25KV high voltage lead in one hand, put
his finger in the anode of a color TV CRT and say "fire it up". Someone
else would plug the set in, and he'd light the screen up with 25K
running through his body. He said no shock could even be felt.

Big deal. He's no doubt well insulated from ground and it's only
about 1 mA max which can't be felt.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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[Beeper]

Thanks, That clears it up for me. I appreciate the info.

 

[Terry]

Wrong again! Many times a sub panel is introduced into the picture and you
run an isolated neutral. by Isolated I mean it is not bonded to the ground
strip. This is done because the Ground is not suppose to have current on
it. It is as Terry said a safety device. If you were to bond the neutral
and ground bars in the sub panel, then the ground would share the current
load back to the main panel.

Appreciate you mentioning that point; and although I have always been aware
of NOT having the neutral and ground in a 'sub panel' connected together, it
reminds me to carefully check one my sub panels to make sure! It is not
likely because the two sub panels, in this house are not the type that would
have been used as a main circuit breaker service panel, with a separate main
breaker.
But one never knows; there might just be a green coloured screw in there
inadvertently connecting the neutral bar to the metal panel box!
BTW ground conductors are often a lesser gauge than the live an neutral
current carrying conductors. I understand that they are sized to more
briefly carry a fault current which then de-energizes the circuit? Ground
wires therefore not amp-gauged for continuous load carrying?
Thanks for the reminder to me.
Terry.

 

[NSM]

I remember science museum demos something along the lines of they would
arrange a line of kids holding hands with the first one's free hand on
the Tesla coil sphere and the last one lighting a fluorsecent tube just
by holding it.

Many years ago a teacher did that with my class when we were 8 yrs old, but
with the spark plug on his car to the frame! Felt like a broom handle run
through my arms.

N

 

[NSM]

Appreciate you mentioning that point; and although I have always been aware
of NOT having the neutral and ground in a 'sub panel' connected together, it
reminds me to carefully check one my sub panels to make sure! It is not
likely because the two sub panels, in this house are not the type that would
have been used as a main circuit breaker service panel, with a separate main
breaker.
But one never knows; there might just be a green coloured screw in there
inadvertently connecting the neutral bar to the metal panel box!
BTW ground conductors are often a lesser gauge than the live an neutral
current carrying conductors. I understand that they are sized to more
briefly carry a fault current which then de-energizes the circuit? Ground
wires therefore not amp-gauged for continuous load carrying?

Yes. There are rules for neutral and ground sizes. I'm prepared to accept
that smart people have worked these out. If I disagree in a special case I
can always run a heavier cable.

N

 

[Sam Goldwasser]

Many years ago a teacher did that with my class when we were 8 yrs old, but
with the spark plug on his car to the frame! Felt like a broom handle run
through my arms.

I guess he didn't quite get it right. Not quite a Tesla coil!

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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Important: Anything sent to the email address in the message header above is
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[NSM]

I guess he didn't quite get it right. Not quite a Tesla coil!

I think someone asked the wrong question. It sure wasn't me.

N

 

[Jim Adney]

Big deal. He's no doubt well insulated from ground and it's only
about 1 mA max which can't be felt.

Our annual "Wonders of Physics" show was the last 2 weekends, and one
of the demonstrations we do every year is this exact one with a Tesla
coil that sounds similar. The guys who do it never seemed to mind, but
they have admitted that it hurts in places, so that you have to be
willing to ignore a bit of pain. The claim is that it tends to hurt at
the ankles and wrists, where the current tends to be concentrated.

Last year one of them talked his daughter into doing it. She nearly
jumped off the stand when it started because she had not been warned
and was not willing to go thru the pain. I suspect that it wasn't
really all that bad, but it was completely unexpected. Still, I have
not volunteered myself for this demo.

OTOH, my own little Tesla coil is completely painless as long as you
are not grounded, but there is a HUGE difference in the size of the
two devices and the sparks that they each make.

-

 

[Jeff Miller]

I think someone asked the wrong question. It sure wasn't me.

N

Good point, not all "tesla coils" are created equal. Those made from TV
flybacks can burn you fiercly: frequency and voltage are too low,
coupling too good, current too high. Some of the Odin coil types and
those built from auto ignition coils (practically the same thing) can
pack a wallop too. Most of the "classic" air-coupled teslas are
harmless, though as has been pointed out they can sting and cause little
welts if the spark lands on bare skin. It depends more on operating
freqancy than voltage.

And I played the tap on the shoulder trick holding a TV anode cable in
high school too. The trick was to get hold of the anode before the set
was switched on, so the voltage ramped up and instantaneous current was
low. It was a long time ago, but as I recall if you had clean rubber
soled sneakers, you could charge up at the set and capacitively carry a
nice pow over to the victim, remote from the set. Is my mind playing
tricks on me? The capacitances and voltages involved don't seem high
enough at first glance, though I clearly remember us torturing each
other as kids with charges accumulated from shuffling on the carpet. On
a good dry day with some expert shuffling a tap on the victim's cheek
could _really_ hurt as well as startle.

I also spent quite a bit of time squeezing train transformer secondary
wires convinced it would make me some sort of superman.

-Jeff