Near the end of the nineteenth century when Westinghouse was
challenging Edison’s dominance of commercial power generation and distribution,
Edison set out to convince the public that AC was far more dangerous — deadly,
even — than DC.
He quietly supplied financial support and resources to an
electrical engineer and consultant named Harold Brown, who was publicly
campaigning for legislation against AC generators and equipment in New York. As
part of his campaign, Brown put on public displays designed to demonstrate just
how much more dangerous AC was compared to DC.
In his first public display, he electrocuted a large black
retriever in a lecture hall at Columbia College at 50th and Madison Avenue in
New York City, much to the disgust of the members of the audience, which
included members of the press, the New York City Board of Electrical Control,
and various other interested parties.
Many of them walked out in the middle of the demonstration,
but Brown persisted until an agent of the American Society for the Prevention
of Cruelty to Animals forbade him to electrocute another dog. The demonstration
ended, but Brown continued his deadly campaign, successfully electrocuting
large dogs, calves, and horses in public.
After one of Brown’s demonstrations, a story ran in The New
York Times describing the grim event. George Westinghouse wrote a letter to the
newspaper in response to the article, defending AC. Brown, in turn, wrote a
letter to the newspaper challenging Westinghouse to a bizarre contest.
“I challenge Mr. Westinghouse to meet me in the presence of
competent electrical experts and take through his body the alternating current
while I take through mine a continuous current….We will commence with 100
volts, and will gradually increase the pressure 50 volts at a time, I leading
with each increase, until either one or the other has cried enough, and
publicly admits his error.”*
Westinghouse didn’t honor him with a reply.
Is AC really more dangerous than DC? There are many factors
that come into play when a person receives a shock. The severity of the shock
depends on the size, weight, age, and body fat of the person, as well as
voltage, frequency, duration of shock, contact area, contact pressure,
temperature, and moisture of the skin.
Generally speaking, the impedance of the skin is the first
line of defense against a fatal shock. It helps prevent current from flowing
through the heart and causing fibrillation. The higher the impedance, the lower
the current for a given voltage.
Like any other electrical circuit, the flow of current
through a human body behaves according to Ohm’s law. It turns out that for AC
current, the impedance of our skin decreases as the frequency increases, but
the frequencies most likely to cause ventricular fibrillation are between 50 Hz
and 60 Hz.
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