I work for a television production company currently producing a show
on the science of safety devices. In this case the safety device is a
GFCI protected outlet on 120V AC U.S. household current.

We are trying to demonstrate the effectiveness of a GFCI protected
outlet in preventing electrocution. We have an indoor lab where we can
eliminate the risk of fire and injury. The half-baked experiment we
have devised is as follows:

We are going to plug a hairdryer into a standard outlet with no GFCI
(the hairdryer does not have its own GFCI on its plug) and turn it on.
We are then going to drop it, using a mechanical arm, into a bathtub
full of tap water. We are going to have a voltmeter with contacts in
the water to measure the power and duration of the charge. We are
assuming that this will not be visually interesting although if it
somehow could be, it would be desired (i.e. sparks, arcing on the
surface etc.).

We are then going to repeat the same experiment with a new hairdryer
plugged into a GFCI protected outlet.

What we want to know is:
Without the GFCI we are assuming the breaker or fuse on our power
source will trip. Will it trip instantaneously, or will we be able to
see a reading held on our meter for a visible amount of time? Will
there be any sparks, arcing, etc?  If we use a generator and eliminate
the breaker will we destroy our generator? Is there a way to do this
using current from our utility, without a breaker, and not knock out our
section of the power grid?

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Clarification of Question by ryandpp-ga on 07 Dec 2005 07:29 PST

Does anyone remember if there were visible sparks and arcing when the
mythbusters did this stunt?

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Clarification of Question by ryandpp-ga on 07 Dec 2005 13:23 PST

I just watched the Mythbusters episode, thanks guys.

At this point we want to find out WHAT we can drop in the bathtub to
get some sort of arcing or flashing. I proposed a  microwave as a
microwave has a transformer which greatly raises the voltage. Correct
me if I am wrong, but I am under the impression that voltage, more so
than amperage, is what makes electricity more likely to arc between
contacts.

What sort of appliance can we be guaranteed to get  visible arcing with?

OK Ryan,
          sometimes the question gets answered in the comments, and
then usually, researchers shrug their shoulders and let it be. You got
lot of comments, and did not expire the question. Comments you got are
a mix of opinions, some true, some silly, and so answer may be 
desirable.

First of all, you should get a real EE to consult for you, hire one or
get a volunteer by calling local chapter of IEEE. Else you are
spreading more myth than you are busting.

Response time: You can NOT show response using a voltmeter. It is too fast. 
-------------

 " For example, at 6mA, UL943 requires the GFCI to
interrupt within 5594msec (5.6 seconds), at 10mA it must
interrupt within 2694msec (2.4 seconds), at 25mA it must
interrupt at 726msec (0.73 seconds) and at 250mA is must
interrupt at 25msec .."

 http://www.bender.org/RCMA473L6-33%20Datasheet.pdf

An EE can show how to hook up a scope which can visualize fast processes.
http://www.doctronics.co.uk/scope.htm


Cheap effects or myth busting?
------------------------------
 " [effects] would be desired (i.e. sparks, arcing on the surface etc.)"

  I see basic problem here, which may explain why popular science on TV is 
usually so bad:
  Either you want to show what actually happens, a demo, may the chips
fall where they will, or you are making a magic show, an illusion.

  To make sparks is not hard - every science museum shop sells plasma globes,
  which use high voltage, high frequency, to make sparks which are  not dangerous:
http://images.google.com/images?hl=en&lr=lang_en&safe=off&q=plasma%20globe

So, if you want to explain something, explain at least what the danger is:

" in order to produce heart fibrillation, an electric power supply
must produce a significant current in the heart muscle continuing for
many milliseconds, and must deposit a total energy in the range of at
least millijoules or higher. Alternatively, it must deliver enough
energy to damage tissue through heating"
http://www.answers.com/topic/voltage-sparks-and-danger

Say a bit about the Ohm Law - it is not that hard to understand.
 http://www.sciencejoywagon.com/physicszone/lesson/otherpub/wfendt/ohmslaw.htm

"Water and hair dryer" is a bit too simple - 
it is more a bogeyman than a real experiment.

Electric shock is result of a current passing through a body.
 Amount of that current depends on the path (from the outlet to the
ground) and on the voltage - as described by the Ohm;s law.

If you get that across to the general public, then you accomplished something.
'Two contacts in water' are meaningless. You want to measure
resistance of the path (from outlet to ground) and perhaps the current
which would pass through the body (if body would be in that path) .
You need visualisation of a response
a scope, not a voltmeter to show it.
http://www.allaboutcircuits.com/vol_1/chpt_3/4.html
http://hyperphysics.phy-astr.gsu.edu/hbase/class/p71d13.html
http://www.hammerzone.com/archives/science/Elec/basic5.html
http://www.allaboutcircuits.com/vol_1/chpt_3/3.html
Hedgie

If I remember correctly, the Mythbusters tested something similar to
this. I can't  remember exactly, but it was Episode 19, "Quicksand." I
don't think there's any way to purchase a DVD of the show, but maybe
you could keep an eye out for it. It might answer some of your
questions and show you the results of their testing.

yes the mythbusters did do that. i think you have a good experment,
but on problem current dosn't run through water, even tap, very well.
you may want to run the experiment with tap water and then add some
soap or a salt to make the current run better through it.

I saw that Mythbusters episode, and to the contrary, it was visually
very entertaining!

Check this out:

Bathtub Electrocution: CONFIRMED - virtually everything they dropped
in the tub registered as a fatal shock.
http://www.tv.com/mythbusters/quicksand-bathtub-electrocution-mri-rays-and-tattoos/episode/368721/summary.html

MYTHBUSTERS - OFFICIAL SITE Episode 19: Quicksand
http://dsc.discovery.com/fansites/mythbusters/episode/episode_06.html
..."Has Hollywood gotten it right all this time? Can you really murder
someone by dropping an electrical appliance into a bathtub? In a truly
electrifying experiment, the guys find out what actually happens when
hair dryer and water collide. Then follow the MythBuilders as they
pursue the case of the exploding tattoo in the MRI. How, if at all,
will the traces of metal found in the ink of Scottie's tattoos react
with the MRI's rays? And Tarzan used it successfully against his
enemies, but will killer quicksand take down the MythBusters? 
premiere: Oct. 20, 2004 ..."

From the Mythbusters Fan Club Site:
http://www.mythbustersfanclub.com/cgi-bin/yabb/YaBB.pl?board=Second_season;action=display;num=1098376015
..."Hair Dryer/Bath Electrocution: Simply put, if someone's in the
bathtub and an electrical appliance gets dumped in with them, the
movies state that it would give enough of a jolt to their system to
kill them. The guys did a good job of simulating the myth, and testing
the current as each item (toaster, curling iron, hair dryer, and
radio, among other things we didn't see) gets dumped into the test
bathtub (using a ballistics gel dummy with metal panels inside to
simulate the human heart). They ended up getting a few things wrong
with the test (like overestimating the amount of ampage needed to kill
someone and minor equipment goofs), but once those were solved, they
were amazed at how well the experiment proved the myth. About the only
object dumped that didn't give over the fatal amount of amps (which
was around 6) was the curling iron, and that still pumped out enough
amps to at least leave you paralyzed long enough to eventually
submerge into the water and drown, or bake to death from the
current...."

I don't know the answers to your questions, but thought I'd pass this along.

I think you should stay away from the microwave.  (Someone please set
me straight if I'm completely wrong, but give a source so I can learn)
 The amount of nonionizing radiation generated by the microwave is
dangerous when not properly shielded by the door or metal case.  I'm
not quite sure what effect the submersion into water would do, but I
wouldn't want to have a surprise.

I did happen to see part of an episode of SCI where they tested an
electrocution with a doll made of a gel that had the same electrical
conductivity than a human body. Having a similar body doll in the bath
could give better visualization for the test. Of course you would have
to make sure that the gel used in that kind of tests is not water
dissolving.

From what I know of high-energy physics you aren't going to get an
electrical light show from dropping anything into a bath tub. The
reason is twofold: water can "hold" an enormous amount of electricity,
so it'll take a lot (probably more than you could provide, if you're
using a full tub of water) to raise the potential of the water to the
point where you could anything flashy to happen.

Second, for flashy stuff to happen you would need to have the
electricity to arc from one place to another place. Given
electricity's affinity for water, you'll have a hard time doing this
to any great degree.

I was thinking if you want a visual representation of what's happening
to the energy supply you could wire up a fake vanity with lights
around the mirror. Have it in the shot as you drop your toaster or
whatever into the bathtub, and have the lights on the same circut as
the toaster. I don't know if you'll get that flickering effect that
you see in movies or if it would just go out.

I think even that your GCFI would kick on before the breaker tripped,
so the power supply with the lights would dim for a split second
before going up to full power again. On the other hand, if you're
recording at 30 or so FPS you'd have to get lucky to capture more than
a couple of frames with the effect.