Figure 4-21.A single-layer porcelain pin insulator.
The pin insulator (fig. 4-21) gets its name from the
fact that it is supported on a pin. The pin holds the
insulator, and the insulator has the conductor tied to it.
Pin insulators are made of either glass or porcelain. The
glass insulator is always one solid piece. The porcelain
insulator is also a one-piece insulator when used with
low-voltage lines but will consist of two. three. or four
layers cemented together to form a rigid unit when used
on higher voltages (fig. 4-22).
The function of an insulator pin is to hold the
insulator mounted on it in a vertical position. Insulator
pins are made of wood or metal. Wooden pins are
usually made of locust. Locust is durable and retains its
strength longer than other woods. Iron and steel pins are
used whenever the pins must be extra long, because of
high voltage, and whenever the tension on the
conductor is great. One make is arranged to encircle the
crossarm as a clamp pinthe clamp being held by bolts
(fig. 4-23). In many cases. a steel rod is used as the base
to permit the use of a 5/8 or a 3/4 hole to be drilled in the
Steel pins are in general use. Steel pins have a broad
base which rests squarely on the crossarm, as shown in
The spacing of the pins is generally suited to the
voltage of the circuit.
The spacing should provide
sufficient working space for the lineman. For general
distribution work, the spacing is 14 1/2 inches between
The post insulators are used on distribution,
substation, and transmission lines and are installed on
Figure 4-22.A two-layer porcelain pin insulator.
Figure 4-23.Steel clamp pin.
wood, concrete, and steel poles.
insulators are manufactured for vertical or horizontal
mounting. The line-post insulators are usually
manufactured as one-piece solid porcelain units or fiber
glass epoxy-covered rods with metal end fittings and
rubber weather sheds. The insulators are fabricated with
a mounting base for curved or flat surfaces, and the top
is designed for tying the conductor to the insulator or
fitted with a clamp designed to hold the conductor.
Line-post insulators designed for vertical mounting are
mounted on crossarms. This type of construction is
often used for long span rural distribution circuits.
Figure 4-25 showsdistribution circuits constructed with
porcelain horizontal line-post insulators. This armless
construction, using post insulators, permits the
construction of subtransmission and transmission lines
on narrow rights-of-way and along city streets.
Figure 4-24.Steel pin.