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 pin - the 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 crossarm.
Steel pins are in general use. Steel pins have a broad base which rests squarely on the crossarm, as shown in figure 4-24.
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 centers.
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.
The line-post 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.Continue Reading