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MMD > Archives > May 2002 > 2002.05.30 > 11Prev  Next


Technically Dead!
By Tom Lear

John Tuttle wrote:

> Can anyone tell me why I'm still here??

Here's why... (Mostly applicable to your situation with normal
household voltages, and this may not be exactly the same for higher
voltages, as when a utility pole is knocked down and the high tension
lines touch earth; there are a few more wrinkles involved in that
scenario..)

The "hot" side of your service is always looking for a "ground" to
complete a circuit.  If it is going through an appliance (load) to
reach the "ground" ("grounded conductor"), it activates the appliance,
in the event the "hot" is directly connected to any "ground", you get
a short circuit and a lot of unpleasant effects.   Either way the "hot"
is always looking for a "ground" to complete the circuit.

This does not address or negate the issue of a 220 circuit where two
"hot" conductors make up the circuit ( no "grounded conductor") .
Adding that in would just unnecessarily confuse matters.

Now in the event there are multiple paths to ground (as in your case),
the "hot" conductor will pick the ones with the least resistance. It
actually will be flowing to all sources of ground, but the majority of
the current flow will go to the least resistant paths.

One of the lesser resistant paths to ground, were the things you had
running on the extension cords, that's why they continued to function.

In a correctly wired residence, the center tap coming off the
transformer in a three-wire system (in this case called the "neutral"
and also the "grounded conductor") , or a two wire system, (in this
case called the "grounded conductor") should be  grounded at the
service entrance Main switch box. This in turn is also interconnected
to a "ground rod"  (usually an 8-10 foot 3/4" brass rod driven into
the earth), and the nearest cold water pipe. In addition, there should
be a jumper wire interconnecting the hot and cold water and gas piping
at the water heater.  Now all your water, gas, and electrical conduit
piping should all be grounded to earth, and hopefully all at somewhat
the same potential.

In the case of lucky Pandora, since the water filling your basement
probably had plenty of various salts and minerals dissolved in it, it
had become an electrolytic solution capable of carrying current.  The
current is going to find the least resistant way to "ground".  The
whole volume of water is going to be a pretty good carrier and
disperser of current, as it is probably coming in contact with multiple
sources of excellent "grounds".  If the basement is cement and wet,
it's in the earth - that's a good conductor, and a huge one,  right
there.  Now if the water is in contact with any water, gas or
electrical conduit piping, you have other good paths to ground. Also
the water will conduct some of the juice right between the prongs in
your extension cords.  If not immersed in a lot of water, you would
see a lot of sizzling and boiling at that point.

OK, so now lucky Pandora is standing in all the water and reaches for
the very excellent "ground" of the water shut off valve for the washer.
Why does she not get fried?  Because the water has already found
multiple ground sources that are already also connected to that water
pipe, so she does not create a new or less resistant path for the
current to flow.

> Evidently, it's a lot more complicated than what is represented in
> the "movies."

For effect, the movies tend to totally misrepresent anything related
to water, electrical, or car disasters, most is far from factual.  I
mean, when was the last time you saw a car crash in a movie that
didn't result in a gigantic fireball.  They always rig all vehicles or
buildings that they are crashing and blowing up, with tons of
accelerants and explosives for extra effect.

I often wonder how many people think the toilet, sink, and shower waste
lines are all somehow interconnected with the incoming water lines?
In the movies if some klutz is trying repair a faucet or some other
fixture, it invariably leads to water shooting all over the room from
the toilet, sink, and shower, drains, and maybe coming out the lighting
fixtures too!!!

All manner of physically impossible or unlikely scenarios with
electricity are played out on the big screen.

OK, now for the classic electrocution-in-the-bathtub scene.

Ideally, assuming someone wants to actually electrocute themselves or
someone else in this fashion...:o) , considering the above, here's how
it would go.  Jump into a fiberglass tub (the tub is not grounded),
drop in the electric heater, now grab the metal tub spout or valve
handles.  Some of the juice is going to go between the connections
right in the  heater, but it's also going to probably find that super
ground source of the metal valves irresistible.  The harder the water,
the better it will conduct the current to you and then from you to the
metal ground source.  Then again, if you're fortunate enough to be
bathing in pure distilled water, you might even get away with it
unscathed.

To prevent such hazards, it is required by the National Electrical Code
that Ground Fault Circuit Interrupters (GFIs) be installed to protect
all plug receptacles near sinks, bathtubs, garages, and ground level
patios, and swimming pools.  Any single duplex plug receptacle  can be
replaced with a GFI as necessary.  If the GFI is on a two-wire  branch
circuit that has other outlets which continue on down the line from
that first GFI protected plug receptacle, the GFI can be wired so that
it also protects those other outlets on down that branch.

Additionally, an entire two-wire branch circuit can be protected
starting from the circuit breaker switch box with a special GFI
enhanced breaker switch.  This is often not possible because many
circuits will start from the box as a three-wire system consisting of
two "hot"  wires sharing one "neutral" "grounded conductor". I won't
elaborate.

All that being said, I still would not want to walk into that basement
water, either.  Always better to err on the side of caution when
working with electricity.  Ideally, you want to be able to get to your
main electrical panel and shut down the entire system before
proceeding.  If you have to go into the water to reach the panel, I
would wear waders and heavy rubber gloves.

And John, this may be a wake up call to upgrade your plug receptacles
to GFIs throughout your residence where needed.  That might well save
you from something worse (like death or a bad burn) in the future.
Easy for you do yourself, and GFIs are cheap at under $10 apiece.

Tom Lear
San Francisco, Ca


(Message sent Fri 31 May 2002, 03:10:25 GMT, from time zone GMT-0400.)

Key Words in Subject:  Dead, Technically

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