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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.