General Order 64-A

Section VII

Detailed Construction Requirements For Trolley Lines

(Class T Circuits)

75.3    Voltage Requirements.

A.    Pin Type.

All pin type insulators used on trolley 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 trolley 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 loading to which they are to be subjected.

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

C.    Tests and Flash-Over Values.

Insulators shall be tested under American Institute of Electrical Engineers specifications at operating frequencies.  The standard of voltage comparison shall be the standard sphere gap voltmeter of A.I.E.E. The dry flash over voltage shall not be more than 75 percent of the puncture voltage.

 

Table 11 Insulator Minimum Flash-Over Voltages
Nominal line voltage	Minimum test dry flash-over voltage
750	5,000
2,300	20,000
4,000	30,000
6,600	40,000
11,000	50,000
22,000	75,000
33,000	100,000

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