General Order 64-A

Section V

Detailed Construction Requirements For Supply Lines

(Class H, L and T Circuits)

55.3    Voltage Requirements.

Insulator used on supply lines shall be so designed that their dry flash-over voltage is not more than 75% of their puncture voltage at operating frequencies.

A.    Pin Type.

All pin type insulators used on supply lines shall be capable of withstanding the voltages given in the following table.

B.    Suspension and Strain Types.

Insulators of this type, when used on supply lines, shall be capable of withstanding the minimum dry flash-over voltages given in the following table when tested with their attaching harness and under the mechanical loadings to which they are to be subjected.

Note.–Equivalent for the standard harness shall be two identical interlocking loops of A.W.G. 1/0 bare hard-drawn 7 strand copper, each linked through the insulator and held with a three bolt 6 inch guy clamp placed on the copper strand at a distance of one foot from the insulator.

C.    Tests and Flash-Over Voltages.

Insulators shall be tested under American Institute of electrical Engineers’ specifications at operating frequencies, and withstand without flash-over the voltages given in the following table.

The standard of voltage comparison shall be the standard sphere gap of A.I.E.E.

For intermediate voltages use the value fo.r flash-over voltages obtained by interpolation.

D.     Additional Insulation.

Insulators used in territories where fog or lightning conditions prevail should be given more liberal factors of safety than those specified in the table above.

Insulators used at crossing or conflicts shall conform to Rules 104.1 and 114.1