Pin Insulator

The pin insulator is used for power distribution for voltages up to 33kV. It is mounted on the cross arm of a supporting tower. The insulator has grooves on the upper end to keep the conductor in place. The conductor is tied to the insulator on the top groove for straight line positions and on the side groove for angle positions with an annealed binding wire made of the same material as the conductor. The insulator body has a lead thimble that is cemented to receive the pin.

The pin insulator comprises non-conductive materials such as porcelain, ceramic, silicon rubber, or polymer. Polymer pin insulators are heavier compared to porcelain insulators.


A single-piece pin insulator is used for low voltage, and for high voltage, two or more pieces are cemented together to maintain the proper thickness. The insulator provides an adequate path for leakage current.

It is important to note that the flashover voltage for moist and dirty surfaces is lower than that for clean and dry surfaces. The total arcing distance through dry air is calculated by adding all the direct distances together, which is represented by (a+b+c). On the other hand, the total arcing distance through wet conditions is calculated by adding (A+B+C).


Advantages of Pin Insulator

  1. The material possesses a high level of mechanical strength.
  2. The pin-type insulator has a reasonable creepage distance.
  3. The high-voltage distribution line utilizes it.
  4. The pin-type insulator is easy to construct and requires minimal maintenance.
  5. It can be used both vertically and horizontally.

Disadvantages of Pin Insulator

  1. It should be used together with the spindle.
  2. It is only suitable for the distribution line.
  3. The maximum voltage rating available is limited to 36kV.
  4. The pin used on the insulator can cause damage to the thread of the insulator.

Causes of Insulator Failure

Insulator failure can occur due to either puncture or flashover. In case of a puncture, the electric current passes through the insulator’s body. On the other hand, flashover is caused by arc discharge between the conductor and the earth through the air surrounding the insulator.

The flashover occurs due to a line surge or wet conducting layer over the insulator’s surface. The insulator remains undamaged by the flashover, but it loses its functionality upon puncture.

The insulator is made with enough thickness to prevent punctures during surge conditions. To reduce flashovers, the resistance to leakage currents is increased. Petticoats or rain sheds are used to construct multiple layers, which make the leakage path longer. The rain sheds keep the inner surface dry during wet weather, providing enough leakage resistance to prevent flashovers.

The use of suspension insulators is preferred for high-voltage work due to the increased size, weight, and cost of pin insulators above 66kV.


In conclusion, a pin insulator is a fundamental component in electrical distribution systems. It provides crucial insulation and support to overhead power lines.

  1. Suspension Insulator
  2. Transposition of Conductors

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