From: Robert M. Hartranft, 75103,2165
TO: "Edwin R. Schweber", INTERNET:EdSchweb@IX.NETCOM.COM
DATE: 5/28/96 11:49 PM
RE: Copy of: Polarized Plugs
Ed:
The usual explanation of household wiring and polarized plugs goes something
like this:
The round, "ground" prong (color code green or bare) is truly a ground: in most
homes, it is connected to a water pipe or to a stake in the ground. It is NOT
connected to the power leads from the utility. Any current in the ground line
is a sign of a short, and if a Ground Fault Interceptor (GFI) is in place, will
trip the circuit. On new construction, GFIs are required in locations like
bathrooms and kitchens.
The larger, "neutral" prong (color code white) is connected to the power
utility, and in some sense is the return leg for the (admittedly AC) supply. It
will carry the same current as the "hot" plug. It is usually very nearly at
local ground, but because local ground can shift with many conditions, may also
be slightly different from local ground potential. Good design practice is to
put components more likely to short in a position where the most likely short is
to neutral.
The smaller, "hot" lead (color code black) is also connected to the power
utility, and will show the typical 110 to 120 volt difference to the neutral
lead. A polarized plug (or a three-prong plug) will maintain these alignments
if everything is wired right. Good practice is to switch on the hot side so
that the greatest part of the circuit is left at neutral potential.
You can demonstrate all this good stuff with a VOM, and I would say to the
benefit of the students.