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Mythbusters

B

Brian Dugas

Jan 1, 1970
0
Did anyone see Wednesday's Mythbusters on Discover Channel?

They were out to test the myth of being electrocuted while talking on a
phone during an electrical thunderstorm. They made a little test
house/shack, and wired it up, and put a dummy talking on a phone, phone was
strapped to his ear. Anyway, it's a long story. They powered up this big
test machinge to 300,000 Volts and it arced to the house. They couldn't get
the test dummy to read any current until they removed the house ground wire.

Anyone see this episode and want to comment on the validity of the test?
I'm curious to see any part of the experiment was unreal.
 
T

TimPerry

Jan 1, 1970
0
Brian Dugas said:
Did anyone see Wednesday's Mythbusters on Discover Channel?

They were out to test the myth of being electrocuted while talking on a
phone during an electrical thunderstorm. They made a little test
house/shack, and wired it up, and put a dummy talking on a phone, phone was
strapped to his ear. Anyway, it's a long story. They powered up this big
test machinge to 300,000 Volts and it arced to the house. They couldn't get
the test dummy to read any current until they removed the house ground wire.

Anyone see this episode and want to comment on the validity of the test?
I'm curious to see any part of the experiment was unreal.

any attempt to make generalizations out of this would be invalid. there are
way too many variables in the equation.

if you are all that worried about it just always use a wireless phone or
cell phone.
 
B

Beachcomber

Jan 1, 1970
0
Even the museums with the largest electric lighting simulators cannot
approach the voltages present in an actual electric strike. It's a
magnitude of millions or billions of volts vs. hundreds of thousands
for the manmade lighting generators.

It's no secret that lighting is destructive and kills hundreds each
year. In a severe electrical thunderstorm, the telephone is just one
such household item to avoid that just happens to be part of an
electrical system in the house. I would avoid taking baths and
showers and usings sinks, basins, washing machines, and toasters, and
hair dryers. The path of a monster lightning strike is mostly
unpredicatable once it actually gets in the house.

The thing is you may have a perfectly working ground that could be
overwhelmed by the tremendous currents from a direct strike. There
are techniques that radio & TV broadcasters use to mitigate lighting
strikes from entering their transmitter shacks. Few homes, though,
have the same degree of industrial protection. For one thing, its
very expensive.

Beachcomber
 
R

Roy Q.T.

Jan 1, 1970
0
I'll be looking @ the dummy through a camera/monitor holding the phone
in a cabin in the middle of nowhere USA };-) with a charge while
lightning is thundering strikes all around.

the lightning documentary i saw on pbs was hot....but who cant predict
or provoke electricity};-)

I have to warn you the big guys don't tell you you're about to Szzt
before you pop something .......... be alert


howoboutit
 
R

Roy Q.T.

Jan 1, 1970
0
Re: Mythbusters

Group: alt.engineering.electrical Date: Thu, Mar 31, 2005, 8:42am
(EST+5) From: [email protected] (Beachcomber)
On Wed, 30 Mar 2005 23:52:14 -0500, "TimPerry"
Did anyone see Wednesday's Mythbusters on Discover Channel?
They were out to test the myth of being electrocuted while talking on a
phone during an electrical thunderstorm. They made a little test
house/shack, and wired it up, and put a dummy talking on a phone, phone
was strapped to his ear. Anyway, it's a long story. They powered up this
big test machinge to 300,000 Volts and it arced to the house. They
couldn't get the test dummy to read any current until they removed the
house ground wire.
Even the museums with the largest electric lighting simulators cannot
approach the voltages present in an actual electric strike. It's a
magnitude of millions or billions of volts vs. hundreds of thousands for
the manmade lighting generators.
It's no secret that lighting is destructive and kills hundreds each
year.   In a severe electrical thunderstorm, the telephone is just one
such household item to avoid that just happens to be part of an
electrical system in the house.   I would avoid taking baths and
showers and usings sinks, basins, washing machines, and toasters, and
hair dryers. The path of a monster lightning strike is mostly
unpredicatable once it actually gets in the house. {{{{TRUE}}}}
The thing is you may have a perfectly working ground that could be
overwhelmed by the tremendous currents from a direct strike. There are
techniques that radio & TV broadcasters use to mitigate lighting strikes
from entering their transmitter shacks. Few homes, though, have the same
degree of industrial protection. For one thing, its very expensive.
Beachcomber
-------------------------
yeap , when you see your hairs about to stand long on ends you know it's
near :)
imagine gettin shunted to earth by one silent translucent bolt, powder
:)

how about a motorized cage/mesh like compartment or/ with a switchable
ground terminal and on rubber wheels. how close was it monitored ????

we'll need the monster capacitor I have right? an, the monster blade
switches from last month for starters }:)>

ohmm, i need a job or a sum/thing


(-:{ ®oykey
 
D

Dwayne

Jan 1, 1970
0
Michael Moroney said:
I didn't see this, but when I was young, we had a summer cottage on a
lake. When thunderstorms were around, the phone would often ring during
a lightning strike, particularly when the storm was east of the place.
We'd joke "It's Mr. Lightning calling; don't answer it!". Sometimes just
a ding, sometimes with more energy. It was a party line; the ringer was
attached to a ground stake. (when they eliminated party lines I don't
think lightning caused it to ring anymore) You may think overhead wiring
would be a cause of all this, but surprisingly the phone wiring in the
area was all underground.

That's freaking hilarious!
~:)

Dwayne
 
A

Anthony

Jan 1, 1970
0
I didn't see the episode but here is how lightning works. It takes
the least conductive path to ground. Every house has an earth wire
buried that is connected to a big metal spike in the ground. If you
have an overhead telephone system (ie: your telephone come from a
nearby pole), then you are at risk. However, if there is a big metal
flag pole nearby (at a restaurant for example) then your fine (as long
as you not in the restaurant). If your worried about your house being
struck by lightning just give a neighbour's kid a kite to play with
and make sure the string is actually a wire.

Dwayne

It actually goes UP from the ground :)



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email
 
D

Dwayne

Jan 1, 1970
0
Brian Dugas said:
Did anyone see Wednesday's Mythbusters on Discover Channel?

They were out to test the myth of being electrocuted while talking on a
phone during an electrical thunderstorm. They made a little test
house/shack, and wired it up, and put a dummy talking on a phone, phone
was strapped to his ear. Anyway, it's a long story. They powered up this
big test machinge to 300,000 Volts and it arced to the house. They
couldn't get the test dummy to read any current until they removed the
house ground wire.

Anyone see this episode and want to comment on the validity of the test?
I'm curious to see any part of the experiment was unreal.
I didn't see the episode but here is how lightning works. It takes the
least conductive path to ground. Every house has an earth wire buried that
is connected to a big metal spike in the ground. If you have an overhead
telephone system (ie: your telephone come from a nearby pole), then you are
at risk. However, if there is a big metal flag pole nearby (at a restaurant
for example) then your fine (as long as you not in the restaurant). If your
worried about your house being struck by lightning just give a neighbour's
kid a kite to play with and make sure the string is actually a wire.

Dwayne
 
B

Brian Dugas

Jan 1, 1970
0
It actually goes UP from the ground :)


I've heard the arguments about lightning going up from the ground. But I
know less about lightning than I do about electricity as a whole. So, until
I have time to do my own homework on this one, I'll just take your word on
it. :)
 
R

Roy Q.T.

Jan 1, 1970
0
It actually goes UP from the ground :)


I've heard the arguments about lightning going up from the ground. But I
know less about lightning than I do about electricity as a whole. So,
until I have time to do my own homework on this one, I'll just take your
word on it. :)


Actually i heard there are 2 kinds the kind that goes up and another
that comes down :-o
 
B

Beachcomber

Jan 1, 1970
0
It actually goes UP from the ground :)


I've heard the arguments about lightning going up from the ground. But I
know less about lightning than I do about electricity as a whole. So,
until I have time to do my own homework on this one, I'll just take your
word on it. :)


Actually i heard there are 2 kinds the kind that goes up and another
that comes down :-o

It is rather complex. When the potential difference between a cloud
and the ground gets to be excessively high (i.e. hundreds or thousands
of millions of volts) two things happen.

A step leader ionized path of lightning comes down from the clouds in
discrete steps descending lower and lower and seeking out a path to
ground. Usually this step leader is invisible to the naked eye, but
it sometimes can be heard as the loud swishing sound just before a
close-by lightning strike.

Similary, the charge on the ground becomes so great that similar
ionized streams of the opposite polarity will come up from the ground,
or more commonly, flagpoles, trees, grounded tv antennas, lightning
rods, church steeples or basically anything that is conductive and
grounded including humans and animals.

When the two streamers meet, the conductive path is complete and the
lighting flashes with the distinctive light and high current
discharge.

A fraction of a second later, what is called the return stroke
discharges in the direction from the earth to the cloud. This is on
the order of from 10 to 1000 times more powerful than the initial
stroke in terms of current magnitude and is the main big bright flash
that is seen and heard as thunder.

To the average person, it looks like the lightning has struck the
ground because it happens in just a fraction of a second. More
properly, the initial step leader and ground streamer have established
the lowest resistance ionized path and, in a fraction of a second, the
return stroke takes place over this ionized path. A special camera is
needed to see the details of how the connection is established because
it is to fast for the human eye to follow.

Beachcomber
 
W

w_tom

Jan 1, 1970
0
Numbers in hyperbole were posted. Lightning is not the
massive destructive energy as implied. Lightning is high
power but not the high energy event so often promoted in
myths. Lightning is a current source - not a voltage source
(as was implied). From basic EE, voltage will rise as
necessary to maintain that current flow. And no, one need not
worry about using a telephone if the human has performed his
job. How a horse is killed when not even struck demonstrates
principles of single point earthing.

Why a single point ground? Same reason why horses can be
electrocuted when a nearby tree is struck. Lightning seeks
earth some 4 kilometers west. So it strikes a tree directly
below the cloud that is east of the horse. Shortest path
westward is up that horse's hind legs and down horse's fore
legs. Horse is killed because it became a good path for
lightning to flow west. Horse conducts electricity better
than earth beneath. Horse became part of an electric circuit.

Same applies to house (building) protection. If using
multiple grounds, then a transient can rise up on a left side
ground rod, find destructive paths through appliances, then
reenter earth via a right side earth ground. Concept is
demonstrated in a NIST figure that demonstrates why bad
earthing can cause fax machine damage:
http://www.epri-peac.com/tutorials/sol01tut.html

How to make a single point ground beneath the horse?
Surround the barn with a buried halo ground. Then earth
beneath the horse becomes one big single point ground -
equipotential. Horse can be killed by a concept that also
kills computers. Therefore better buildings also install halo
grounds or Ufer grounds. Earth ground - not a UPS or power
strip protector - being so important for computer hardware
(and horse) protection.

An introduction to concepts of building (and electronic)
protection is provided at:
http://www.bb-elec.com/tech_articles/dataline_surge_protection.asp

Protection from lightning is first and foremost about
earthing. Yes, even the household earth ground provides a
massive improvement in both human and transistor protection.
But for protection from rare, higher energy lightning strikes
(that you may never observe in your lifetime), utilities
install massively larger earth grounds. Major expense only
to marginally improve their earthing system - because
reliability is that critical.

Removing a building's earth ground (or connection from each
incoming utility to that single point earth ground) puts the
human (and transistors) at greater risk from lightning.
Reason to not use a phone during a thunderstorm? A human has
failed to install or has compromised the building's earthing
system. This should never happen in an EE's building.

The myth busters demonstrated what we have long understood
even before transistors were invented. Effective protection
has always been first and foremost about the essential single
point earth ground. Not about pointed verses blunt rods, not
about preventing lightning (ESE devices), not about blocking
the resulting transients, and not about miracle plug-in
protectors that will somehow absorb what miles of sky could
not. Protection has always been about shunts; diverting a
direct strike to earth ground on an electrically shorter and
non-destructive path.
 
W

w_tom

Jan 1, 1970
0
You are confusing the construction of a 'plasma wire' (what
we call lightning) with something completely different: the
electrical discharge through that wire.
 
D

Don Kelly

Jan 1, 1970
0
w_tom said:
Numbers in hyperbole were posted. Lightning is not the
massive destructive energy as implied. Lightning is high
power but not the high energy event so often promoted in
myths. Lightning is a current source - not a voltage source
(as was implied). From basic EE, voltage will rise as
necessary to maintain that current flow. And no, one need not
worry about using a telephone if the human has performed his
job. How a horse is killed when not even struck demonstrates
principles of single point earthing.

Why a single point ground? Same reason why horses can be
electrocuted when a nearby tree is struck. Lightning seeks
earth some 4 kilometers west. So it strikes a tree directly
below the cloud that is east of the horse. Shortest path
westward is up that horse's hind legs and down horse's fore
legs. Horse is killed because it became a good path for
lightning to flow west. Horse conducts electricity better
than earth beneath. Horse became part of an electric circuit.
---------------
The horse is not killed because the lightning wants to "go west" ground due
to high ground current radiating out from the tree (natural ground rod)
through resistive ground. There will be a step potential between the
horses legs because of this so that there will be a small part of the
current through the horse (if large then the horse is cooked, not
electrocuted). If the horse could stand with all feet together it would be
OK if not too close to the trunk of the tree.
---------------
Same applies to house (building) protection. If using
multiple grounds, then a transient can rise up on a left side
ground rod, find destructive paths through appliances, then
reenter earth via a right side earth ground. Concept is
demonstrated in a NIST figure that demonstrates why bad
earthing can cause fax machine damage:
http://www.epri-peac.com/tutorials/sol01tut.html
------------
This source does indicate the transient problem but doesn't fit your
description. It is a case of a long path between the entance and a single
ground. This is also a factor in the case of lightning striking a power
transmission tower. If multiple grounds, there may or may not be an
appreciable voltage build up, depending on many factors but the net effect
will be lower voltages than with a single ground. However, you are right
with respect to "proper grounding" .
---------
How to make a single point ground beneath the horse?
Surround the barn with a buried halo ground. Then earth
beneath the horse becomes one big single point ground -
equipotential. Horse can be killed by a concept that also
kills computers. Therefore better buildings also install halo
grounds or Ufer grounds. Earth ground - not a UPS or power
strip protector - being so important for computer hardware
(and horse) protection.

An introduction to concepts of building (and electronic)
protection is provided at:
http://www.bb-elec.com/tech_articles/dataline_surge_protection.asp

Protection from lightning is first and foremost about
earthing. Yes, even the household earth ground provides a
massive improvement in both human and transistor protection.
But for protection from rare, higher energy lightning strikes
(that you may never observe in your lifetime), utilities
install massively larger earth grounds. Major expense only
to marginally improve their earthing system - because
reliability is that critical.

Removing a building's earth ground (or connection from each
incoming utility to that single point earth ground) puts the
human (and transistors) at greater risk from lightning.
Reason to not use a phone during a thunderstorm? A human has
failed to install or has compromised the building's earthing
system. This should never happen in an EE's building.
----------
Possibly I am missing your point but Multiple well separated (too close
together and only a slight benefit exists with respect to a single rod)
ground rods will be more effective than any single rod - IF the rods are
interconnected properly. If not, then there will be no benefit. Note that
utilities will use many rods in a switchyard but will interconnect these at
or under the surface by a grid- to achieve both low ground resistance as
well as an approximately equipotential surface.
---------------
The myth busters demonstrated what we have long understood
even before transistors were invented. Effective protection
has always been first and foremost about the essential single
point earth ground. Not about pointed verses blunt rods, not
about preventing lightning (ESE devices), not about blocking
the resulting transients, and not about miracle plug-in
protectors that will somehow absorb what miles of sky could
not. Protection has always been about shunts; diverting a
direct strike to earth ground on an electrically shorter and
non-destructive path.
------
Agreed but the key factor here is low ground resistance more than short
distances. It is a matter of incoming line surge impedance vs ground
resistance. It is also a factor that protective equipment should be as close
as possible to the equipment being protected. It is less about "shunts" than
about the behaviour of surges and reflections where changes in surge
impedance occur.

--
Don Kelly
[email protected]
remove the urine to answer


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