Post by Questor Post by Charles Bishop
Following links from another post, I ran across a video of a woman
explaining why a relative of hers (teen?) died while in a bathtub with
her cell phone nearby (on the edge, possibly). The cell phone was
connected to a charger which was plugged into 120V.
If only the cell phone and the low voltage end of the charger's cord
fell into the water, would this be enough to electrocute someone? It was
disturbing, so I didn't watch the video further to see if more details
were given, such as the charger was plugged into an extension cord and
that part fell into the water.
Based on Greg's post it sounds like an extension cord and possibly other factors
were involved that resulted in wall current being transmitted to the bath water.
My understanding is that the low voltage supplied by chargers should not be an
electrocution threat, however I am not whatsoever inclined to do the empirical
research necessary to confirm this hypothesis. If Greg's comments about
transformer-less design don't give one pause, just general life experience
that "sometimes things just go wrong" should. I would rather not be another
tidbit in one of those "strange but true" features.
Decades ago, in a hobby electronics magazine's Q&A column a reader asked which
was more dangerous: low current at high voltage, or high current at low
voltage? I don't recall that there was a definitive answer, other than that due
to the unpredictability of the path taken by electricity through the body,
either one of those alternatives was likely to ruin your day.
Voltage is also known as electromotive force, and can be thought of in some
sense as the electrical "pressure." Current is the quantity of electrons. My
guess is that relatively few electrons forced through the body at high pressure
is worse than a lot of electrons conducted through the body with low force, but
so much is dependent on where they go. Both alternatives have the potential to
fatally disrupt the body's own electrical processes.
In the less safety-conscious sixties my school's physics department put on
some class project demos a part of the school's annual fair. These included:
* A demo of a Van de Graaff generator in which a volunteer kid gripped the
relevant contact while standing on a wooden stool, so that parents and other
visitors could watch as the kid's static charge rose to half a million volts
(at a minuscule fraction of an amp) and his hair rose to stand on end... at
one point the lab got too crowded and a visiting mum was accidentally pushed
into the kid: there was an incredibly loud SNAP! as the two were thrown
backwards into other bystanders; luckily neither had a weak heart and both
were fully recovered (apart from a little residual shock) within five
* A step-down transformer utilising rheostats--which would themselves get
red hot--that we used to melt six-inch galvanised nails by passing 600 amps
at a fraction of a volt through it. I'm damn glad that no-one got pushed
into *that* device, which was most definitely not safely caged so that
no-one could accidentally touch it--with probably deadly effect.
Regards, Peter Boulding
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