Its not uncommon for a character in the
movies to end up with a blackened face and a headful of frizzy hair after touching al ive electrical wire.
What makes for a good
gag in the entertainment biz, however, is
likely to kill you in real lifeunless youre
a bird. Birds have no problem sitting,
unruffled, on the high-voltage power lines
you often see lining the road. This ability
has nothing to do with them being birds,
explains Ranbel Sun '10, MNG '13, a recent grad in electrical engineering who
currently teaches at Phillips Academy in
Andover, Massachusetts. Its all about the
connections theyre makingor, more
importantly, not making.
Electrical current is the movement of
electrons, explains Sun. The movement of electrons through a device like your TV is what gives it the energy to display images and produce sound. Sun describes the long process these moving electrons take to get to your house.
The electrons are essentially
being pulled from the ground by the power
station, she says. They move through the power lines, through your TV, and
eventually they make their way back into
the ground from where they came. This
creates a closed loop, which is required for electricity to flow.
The other thing electrons need in order to
move is motivationor, more specifically, a
difference in whats called electrical
potential. Imagine lugging a bunch of
bowling balls up a mountain, Sun
explains. If you give them a path, the balls will naturally roll down the mountain to a lower position. At the top of the mountain,
the bowling balls (which represent the
electric current) have a high potential, and
they will travel down any path that
becomes available.
When a bird is perched
on a single wire, its two feet are at the same
electrical potential, so the electrons in the
wires have no motivation to travel through
the birds body. No moving electrons means
no electric current. Our bird is safe, for the
moment anyway. If that bird stretches out a
wing or a leg and touches a second wire,
especially one with a different electrical
potential, it will open a path for the
electronsright through the birds body.
There are other perils for our feathered
friends, Sun points out. The wood pole
supporting the wires is buried deep in the
ground, she says, so it would also be
dangerous for a bird to sit on the pole and
touch a wire. This is the problem that
people encounter if they touch live wires
since we are almost always in contact with
the ground. Our bodies turn out to be
excellent conductors of electricity, and the
electrical current will happily use them to
complete a closed path to flow from high
potential (the wire) to low potential (the
ground). ZAP!
So how do workers repair live electrical
wires without getting hurt? They use
insulating materials in their clothing,
equipment, and bucket trucks. Insulating
materials such as rubber are materials
through which electricity has a hard time
flowing. So instead of passing through the
electrician, the electrons stay on the other
side of his rubber gloves or rubber-handled
tools. (Keep in mind: these are not everyday
household gloves and toolsthose are too
thin to protect you from a shock and are
often not made entirely of rubber) Another
technique is to hang beneath a helicopter.
Since neither the worker nor the helicopter
is connected to the ground (like a bird), the
worker just has to make sure he only
touches one wire at a time. Despite
continual safety improvements, being a
power linesman is still one of the 10 most
dangerous jobs in America. So, its a good
idea to stay away from electrical wires
unless youre a trained professionalor a
bird.
Now if only someone could explain why
birds are always all facing in the same
direction
