04.19.08
Magnet Wire
Magnet Wire. The wire used in winding magnets is, of course, an
important part of the electromagnet. It is always necessary that the
adjacent turns of the wire be insulated from each other so that the
current shall be forced to pass around the core through all the length
of wire in each turn rather than allowing it to take the shorter and
easier path from one turn to the next, as would be the case if the
turns were not insulated. For this purpose the wire is usually covered
with a coating of some insulating material. There are, however,
methods of winding magnet coils with bare wire and taking care of the
insulation between the turns in another way, as will be pointed out.
Insulated wire for the purpose of winding magnet coils is termed
_magnet wire_. Copper is the material almost universally employed for
the conductor. Its high conductivity, great ductility, and low cost
are the factors which make it superior to all other metals. However,
in special cases, where exceedingly high conductivity is required with
a limited winding space, silver wire is sometimes employed, and on the
other hand, where very high resistance is desired within a limited
winding space either iron or German silver or some other
high-resistance alloy is used.
_Wire Gauges_. Wire for electrical purposes is drawn to a number of
different standard gauges. Each of the so-called wire gauges consists
of a series of graded sizes of wire, ranging from approximately
one-half an inch in diameter down to about the fineness of a ladys
hair. In certain branches of telephone work, such as line
construction, the existence of the several wire gauges or standards is
very likely to lead to confusion. Fortunately, however, so far as
magnet wire is concerned, the so-called Brown and Sharpe, or American,
wire gauge is almost universally employed in this country. The
abbreviations for this gauge are B.&S. or A.W.G.