Date: Fri Mar 26 15:40:46 2010

Author: Zani, Gerald

Subject: Re: Ground Fault Interrupter - How Much Safety? 2

Post:

I believe you are incorrect. - Jerry

-----Original Message-----
From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Marc "Zeke" Kossover
Sent: Friday, March 26, 2010 3:26 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] Ground Fault Interrupter - How Much Safety? 2


By Zani, Gerald
Sent: Friday, March 26, 2010 1:24 PM

>The GFCI gives no protection for the two wire pickle
>because there is no ground wire.
>
>The pickle is exceedingly dangerous because of
>this.

With no disrespect intended, especially with the amount I have learned
here, that is not true. GFCI are much more reliable and more capable
than you are giving them credit.

This experiment is dangerous because you can grab both electrodes with
two different hands and have lethal current across your heart if your
resistance between your hands is low enough.

A working GFCI will protect you if you touch the pickle with one hand.
The lack of a ground wire does not affect affect the operation of the
GFCI. In fact, many local electrical codes will let install a 3-prong
GFCI into an outlet which has no normal ground as the GFCI gives more
protection against electrocution than a ground wire does.

The GFCI compares the hot wire to the neutral wire usually through a
transformer where those two wires make up one side of the transformer.
When the current in each wire is the same (but opposite in direction)
the net electrical flux is zero and so no current is induced on the
other side.

On the other hand, if current is leaking through a hand and to the earth
through a hand that is touching the pickle, the current in the hot side
will not equal the current in the neutral side. The net flux will induce
current in the output side of the transformer, and that will cause it to
disconnect the hot side of the circuit.

The ground wire doesn't come into play.

Of course, in principle, this doesn't protect you if you grab both
electrodes because the current in the hot side will be the same as in
the neutral side. In practice, you usually still have some protection
(but not fail-safe) because you may be connected to the earth well
enough to get more than 5 mA leaking from you to the earth. That
difference is enough to trip the GFCI.

GFCI's are amazing devices. I have them installed on all circuits in the
lab. You can even get them to add to extension cords.


The one bad thing about GFCIs is that they are often tripped by Tesla
coils.

Z

You could get
>killed coming between the hot and the neutral and
>therefore there is
>zero benefit even if using a GFCI. Because!! the
>ground safety
>connection is excluded! and the GFCI will not protect
>you.
>
>A GFCI only protects if and when the hot and/or neutral
>currents are
>shorted into the ground wire.
>
>Such is not the case if you get shocked by the pickle and
>its two wires.
>
>
>A GFCI circuit is a Ground Fault Circuit Interrupter and
>no safety
>occurs when there is no ground third wire.
>
>- Jerry
>
>
>
>-----Original Message-----
>>From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
On Behalf
>Of Marc "Zeke" Kossover
>>Sent: Friday, March 26, 2010 1:05 PM
>>To: tap-l@lists.ncsu.edu
>>Subject: Re: [tap-l] cheap spectrum lamp
>
>From: chuck britton
>
>>To get the GFI
>protection one would have to have one hand
>> firmly grasping a
>cold water pipe (or other EXTERNAL ground) when touching the
>> device.
>
>That's not true. GFI are
>explicitly designed for situations where the person is not thoroughly
grounded.
>
>Let's imagine that a
>person is poorly connected to the earth so that they have a very large
>resistance. That might not set off the GFI since it needs a few
milliamps of
>current difference to be activated, but then the person will only have
a few
>milliamps of current flowing through him or her.
>
>If they have a low enough
>resistance to get more than a few milliamps through them, then they
will set
>off the GFI and the circuit will be interrupted.
>
>On the other hand, if you
>grab both electrodes and are well insulated from the ground, you might
in fact
>truly kill yourself. That's why I covered the electrodes with shrink
wrap over
>the whole bit that is inserted. And I put the blast shield in front of
it to
>keep someone from grabbing the pickle.
>
>Zeke Kossover
>
>
>
>
>
>-----Original Message-----
>>From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
On Behalf
>Of chuck britton
>>Sent: Friday, March 26, 2010 1:05 PM
>>To: tap-l@lists.ncsu.edu
>>Subject: Re: [tap-l] cheap spectrum lamp
>
>OK, I get you.
>
>If you are standing in a
>pool of water and touch the hot electrode,
>either a GFI or the
>isolation transformer could be expected to save
>your life.
>
>I'm still worried about
>the possibility of touching BOTH electrodes
>while installing the pickle.
>If the device is 'hot' and
>you contact EACH side of it - I don't see
>how either of these
>protective devices is going to make a whit of
>difference.
>
>The GFI doesn't know (or
>care) if the current is flowing thru you or
>thru the pickle.
>The GFI compares the
>current provided by the 'hot' lead to the
>current returned by the
>'neutral' lead.
>Current leaking to
>'ground' is required to trip the circuit.
>
>Before the days of GFI's
>in the kitchen, toasters were not allowed to
>have grounded (3-prong)
>plugs.
>This reduced deaths from
>the common scenario of someone poking into
>the toaster with a bare
>knife blade while resting the other hand on
>the metal body of the
>toaster. (Toasters always had exposed 120 VAC
>heating elements back in
>those 'good old days'.)
>
>Some electrical codes
>still do not allow some kitchen appliances to
>have a grounded chassis.
>
>I'm certainly NOT opposed
>to safety devices.
>I just want people to
>understand that the protection is VERY limited
>and not to be counted on
>to cover all circumstances.
>
>This particular demo is
>fraught with very real danger.
>
>Neither the GFI nor the isolation transformer comes CLOSE to
>protecting the operator.
>
>
>At 9:34 AM -0700 3/26/10,
>Bill Alexander wrote:
>>The isolation transformer
>only provides a similar protection to the
>>GFI, that is, one lead
>to ground should not hurt you.
>
>
>
>
>
>-----Original Message-----
>>From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
On Behalf
>Of Dale E. Stille
>>Sent: Friday, March 26, 2010 1:01 PM
>>To: tap-l@lists.ncsu.edu
>>Subject: Re: [tap-l] cheap spectrum lamp
>
>Tappers,
>
>To make the pickle
>experiment as safe as possible, you should have three
>levels of safety just like
>NASA.
>
>1. Have the wall
>plug pulled when setting up the demo and don't plug it
>in until you are ready to
>use it.
>
>2. Have an arming
>switch that needs to be turned on before the demo can
>be used.
>
>3. Have a
>"momentary on " pushbutton switch in the circuit that must be
>held down to allow
>electricity to flow thru the pickle. Take you finger
>off the push button and
>the demo stops.
>
>Any two of these can be
>left on and your bumbling PHD types will still
>survive........
>
>Dale Stille
>U of Iowa
>
>Bill Alexander wrote:
>> The isolation transformer
>only provides a similar protection to the GFI, that is, one lead to
ground
>should not hurt you.
>>
>>
>> And I don't see how
>the previously mentioned isolation transformer
>> would provide any
>protection either.
>> (but maybe that
>comment wasn't implying such)
>>
>> This is a VERY
>dangerous experiment.
>> I built one for our
>HS and no one has died from it.
>> I ALWAYS kept the
>'Kevorkian Cord' (two prong plug with alligator
>> clips) in my pocket
>and only plugged it into a very visible, switched
>> extender outlet. My
>colleagues seemed to respect its lethality.
>>
>>
>> At 10:46 AM -0500
>3/26/10, Paul Nord wrote:
>>> Can you eliminate
>the sparking by making good contact at many points
>>> on the
>pickle? Perhaps make a pincushion of nails on each end?
>>
>
>
>
>
>
>-----Original Message-----
>>From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
On Behalf
>Of chuck britton
>>Sent: Friday, March 26, 2010 12:27 PM
>>To: tap-l@lists.ncsu.edu
>>Cc: Paul Nord
>>Subject: Re: [tap-l] cheap spectrum lamp
>
>the 'Four Tined Fork at
>each end' approach doesn't reduce the effect.
>Dissection (sometimes by
>mastication) has showed that all four tines
>take part in the
>discharge.
>Perhaps not all four at
>once.
>If one tine fires first -
>I suspect that it will 'dry out' its
>environment - making one
>of the other tines more likely to fire.
>
>Please remember that a GFI
>will NOT protect someone who happens to
>complete the circuit
>across this device!!!!
>
>To get the GFI protection
>one would have to have one hand firmly
>grasping a cold water pipe
>(or other EXTERNAL ground) when touching
>the device.
>
>And I don't see how the
>previously mentioned isolation transformer
>would provide any
>protection either.
>(but maybe that comment
>wasn't implying such)
>
>This is a VERY dangerous
>experiment.
>I built one for our HS and
>no one has died from it.
>I ALWAYS kept the
>'Kevorkian Cord' (two prong plug with alligator
>clips) in my pocket and
>only plugged it into a very visible, switched
>extender outlet. My
>colleagues seemed to respect its lethality.
>
>
>At 10:46 AM -0500 3/26/10,
>Paul Nord wrote:
>>Can you eliminate the
>sparking by making good contact at many points
>>on the pickle?
>Perhaps make a pincushion of nails on each end?
>
>





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