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General Order 64

 

Section VI

 

Detail Construction Requirements For Supply Lines

 

64    Insulators.

 

(a)    Insulators used on supply lines shall be porcelain, glass or other equally suitable material.

The insulators shall be so designed that their dry flash-over voltage will be less than their puncture voltage, at 60 cycles frequency.
  Strain insulators shall be capable of withstanding under their mechanical loading at least as high a voltage as line insulators in general.

 

(b)    Insulators shall be capable of withstanding without flash-over at a frequency of 60 cycles, the voltages given in the following table:

 

Table 6

Insulator Minimum Flash-Over Voltages

Voltages of circuit

Flash-over voltage

Dry

Wet – 1-5 inch

rain per minute – 45°

750

5,000

3,500

2,300

11,000

8,000

4,000

17,000

13,000

6,600

27,000

17,000

7,500

30,000

18,000

11,000

40,000

20,000

15,000

55,000

25,000

22,000

75,000

40,000

33,000

105,000

65,000

44,000

125,000

85,000

55,000

150,000

100,000

66,000

170,000

115,000

88,000

225,000

165,000

110,000

275,000

200,000

150,000

350,000

250,000

200,000

450,000

300,000

 

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

 

(c)    All insulators or insulator units, used on lines on which the voltage exceeds 17,000, shall be subjected to flash-over test at frequency of 60 cycles, or to such other tests as may be generally sanctioned by good modern practice.

 

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

 

(e)     Insulators, supports, clamps and miscellaneous attachments shall be designed to withstand with the designated factors shall be designed to withstand with the designated factors of safety, the tension in conductors, wires or structures under the loading conditions as specified herein.