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How
does the grounding wire in an A.C. circuit protect against electrical
shock? P.L., via e-mail
Coming
in contact with a hot wire while standing on a grounded, conductive surface
will allow your body to become a parallel return conductor to ground and
result in you experiencing an electrical shock. The ground wire provides
the current with an alternative low-resistance return path to ground.
The
accompanying illustration explains how this works. In the first diagram
we have an A.C. motor hooked up to a two-wire system: hot (black insulation)
and neutral (white insulation). Both wires are supposed to be isolated
from one another as well as from the metal case of the motor. However,
let’s assume that the hot wire’s insulation has failed and
so the conductor is in contact with the metal motor casing. The motor
will continue to operate normally, but since the casing is “hot,”
coming in contact with it will produce the same result as touching the
wire itself.
In the
second diagram, a ground wire (green insulation) is connected to the neutral
wire at the power source and runs parallel to it throughout the system.
Connecting this wire to the exterior of the metal case of every electrical
device—in this case the motor—in the circuit will offer the
stray current a low-resistance path to ground. Furthermore, should the
short be of low enough resistance, the current will trip the circuit breaker
or blow the fuse of the black conductor. (For this reason, never install
a switch, circuit breaker, or fuse in the green grounding conductor.)
But even if the breaker or fuse doesn’t trip or blow, the green
wire will still provide a safe route back to ground.
What
is the proper way to care for isinglass, and how can I protect the zippers
and snaps? K.P., via e-mail
Wash
your isinglass panels before you roll them up to prevent dirt and salt
from scratching the surface. Simply hosing with fresh water and drying
with a clean chamois cloth will do the trick. I’ve found that using
products such as Meguiar’s Mirror Glass #17 or Star brite’s
Plastic Polish Restorer after a thorough washing works well as these form
a protective layer that surface dirt doesn’t easily adhere to.
For
isinglass that is already scratched, try Star brite’s Plastic Scratch
remover. It will gently rub out the scratches, after which you can follow
up with polish. And remember, once isinglass turns brown or yellow, it
must be replaced.
As far
as keeping snaps and zippers working properly, frequent freshwater dousings
will help to remove salt buildup, especially after tying up for the day.
A little WD-40 applied with a cotton swab usually works well.
For
added protection, I’ve used Star brite’s White Teflon Snap
& Zipper Lubricant on Office Ours, PMY’s company boat, and found
that a once- or twice-a-season application keeps things running smoothly.
All these products are available in most marine supply stores.
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