8 inches. When more than one pair of wires are strung on the same poles, the spacing between wires usually is 10 or 12
inches, depending on the type of cross arms in use.
(2) The wire diameters most frequently used for open wire lines range from 80 mils to 165 mils (1 mil is
equivalent to 1/1,000 inch).
b. Cables. Cables may be described as consisting of one or more pairs of wires, each wire individually
insulated; the wires of a pair are twisted together, the pairs usually are twisted together, and the entire group is covered
with an outer covering. Two types of cable frequently used military installations are illustrated in figure 51.
(1) Spiral-four cable contains four conductors, in two pairs (fig. 51). Each conductor is made up of seven strands
of copper, and is covered with a polyethylene insulation. The insulation on one pair of conductors is light colored, and
that on the other pair is dark, to facilitate identification of circuits. The insulated conductors are spiraled around a
polyethylene core. A polyethylene belt surrounds the spiraled conductors, and is in turn surrounded by black carbon tape.
Around the tape is a stainless-steel braid, to provide mechanical strength for the cable. This is covered by an outer jacket
of vinyl.
(2) Five-pair rubber cable contains ten conductors, arranged in five pairs, as shown.
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