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General Order 64-A

 

Section V

 

Detailed Construction Requirements For Supply Lines

(Class H, L and T Circuits)

 

54.4    Clearances

 

A.    Above Ground.

 

(1)    Normal:  The normal minimum vertical clearances shall be those specified in Rule 35, Table 1.  Notes following this Table are references to the rules which modify the normal minimum clearances.

 

(2)    Across Arid or Mountainous Areas: Across arid or mountainous areas supply circuits carrying 17,000-25,000 volts, inclusive, may have a clearance of 25 feet from the ground.  Upon special permission from the Railroad Commission this clearance may be applied to circuits in excess of 25,000 volts.

 

(3)    Lead Wires for Transformers:  Where the installation is made in accordance with Rule 58.4-F a minimum distance of 20 feet shall be maintained.

 

B.    Above Railways

 

(1)    Tracks:

 

a)    Trolley Throw:  A maximum trolley pole throw of 26 feet above rail is the basis of the clearances of Table 1, Case 2.  For railways (except railways transporting standard freight cars) having a trolley throw at variance to this, the clearance may be reduced and shall be increased accordingly, provided that in no case (other than specified in Rule 57.4-E and Table 1, Col. C) shall it be less than 25 feet.  In Table 1, Col. F, the clearance shall not be less than 30 feet.

 

b)    Freight Cars:  Freight cars measuring 15 feet from top of the rail to the running board are the basis for the clearances of Table 1, Case 1.  These clearances may be reduced a maximum of 2 feet for cars of a lesser height to afford the same clearance above such cars.

Where freight cars exceed the 15 foot dimensions above, the vertical ground clearance shall be increased accordingly to provide the same clearances between conductors and top of car.

 

(2)    Trolley Conductors:  Cables, guys and messengers which are suitably protected, shall have a clearance not less than 4 feet above the trolley contact conductor, provided they are not less than 23 feet above tracks on which standard freight cars are not transported or proposed to be transported.

 

C.    Between Conductors

 

(1)    Normal:  The normal minimum horizontal and vertical clearances shall be those specified in Rule 36, Table 2.  Notes following this table are references to the rules which modify the normal minimum clearances.

 

(2)    Allowable Variation:  Allowable variations in clearances due to side swing of suspension insulators, temperatures, long spans, etc., are given in Rules 35 and 36.

 

(3)    Different Voltage Classifications:  Supply circuits of different voltage classifications may be supported on the same crossarms as specified in Rule 32.5.

 

(4)    Circuits of 750-7500 Volts:  The 4 foot vertical clearance between circuits of 750-7500 volts, as specified in Table 2, Case 10, Column E, may be reduced to 2 feet if all circuits are of one ownership and operated by the same crews of workmen and it is not practicable to obtain greater clearance, provided buck arm construction is not involved.  This 2 foot clearance may also apply between cables (treated as in Rule 57.8) where attached directly to one side of pole.

 

(5)    Circuits of 7500-17,000 Volts:  The 4 foot vertical clearance between circuits of 7500-17,000 volts, as specified in Table 2, Case 11, Column F, may be reduced to 3 feet if all circuits are of one ownership and operated by the same crews of workmen and it is not practicable to obtain greater clearance, provided buck arm construction is not involved.

 

(6)    Triangular and Vertical Configuration: Crossarms used to support conductors of a circuit at different levels as in triangular or vertical configuration need not be spaced as in Table 2, Cases 8 to 13, but may be arranged so that the vertical separation of conductors of the same circuit shall be not less than the pin spacing of Table 2, Case 15, provided that if more than one circuit is concerned all circuits on the arms shall be similarly arranged and that the spacing specified for the higher voltage shall be used in the event different voltage classifications are involved.

Conductors dead-ended on a pole in vertical configuration be means of strain insulators shall maintain the clearances of Table 1, Case 7 and Table 2, Case 8 to 13, inclusive.  Where more than one circuit is installed on a pole in this manner, the conductors of the lower circuit or circuits shall be so dead-ended that no energized part thereof is less than 2 feet from the surface of the pole for voltages of less than 7500 and 3 feet from the surface of the pole for voltages in excess of 7500.

 

(7)    At Top of Pole:

 

a)    0-7500 Volts:  Any single conductor of a circuit of 0-7500 volts may be attached directly to the top of a pole provided the other conductors of a circuit are on a horizontal plane at least 2 feet vertically below such conductor.

 

b)    More than 7500 Volts:  Any conductor of a circuit carrying in excess of 7500 volts may be attached directly to the top of a pole or to a crossarm at the top of a pole at a distance less than specified in Table 1, Case 7, provided such conductor is not less than 6 feet above the conductors of any other circuit on the pole and that no transformer or other apparatus (excepting pole top switches) carried on the pole is connected to the circuit in the upper position.

 

(8)    Rack Construction (See Rule 54.9-B.)

 

(9)    Voltages of More Than 68,000:  The vertical separation between conductors on related line arms and buck arms and the horizontal separation of wires on cross arms (pin spacing) shall be increased inch for each K.V. above 68 K.V. (See Table 2, Case 14 and 15, Column I.)

 

(10)    Duplex or Triplex:  (See Rule 57.4-C.)

 

D.    From Poles.

 

(1)    Lateral Conductors:  Lateral conductors of open wire construction (not in cable) shall not be attached to the surface of poles (excepting ground wires as specified in Rule 54.6 and bond wires, as specified in Rule 53.4),  but shall be supported on cross arms or other supports arranged to maintain the clearance from poles, towers or structures and other conductors (as specified in Table 1, Cases 7 and 9, and Table 2, Case 16), and to maintain the climbing and working spaces as required in Rule 54.7; or they shall be enclosed in conduit or otherwise protected by suitable covering.

 

(2)    Vertical Conductors:  Vertical conductors of open wire construction (not having a suitable protective covering) shall not be attached to the surface of poles (excepting ground wires as specified in Rule 54.6) but shall be supported on crossarms or other supports arranged to maintain the clearance from poles, towers or structures and other conductors (as specified in Table 1, Cases 7 and 9, and Table 2, Cases 15 and 16), and to maintain climbing and working spaces as required in Rule 54.7.

 

(3)    Center Line:  Wires run adjacent to a pole and unattached thereto shall be maintained, at all times, so that the distance of any wire to the center line of the pole specified in Table 1, Case 7, is maintained.  This rule will often necessitate the use of clearance arms.  (See Rule 57.4-F for cables.)

The clearances referred to in Table 1, Case 7 Column E, apply as follows:

 

750-7500 volts - - - - - - - - 15 inches
7500-17,000 volts- - - - - - 18 inches

 

(4)    Dead Ends:  The clearance of the conductors from the surface of the pole shall not be less than that required for incidental pole wiring as given in Table 2, Case 16.  (See Rule 54.4-C6.)

 

(5)    Rack Construction:  A 3-inch minimum clearance from surface of poles is required for all span lengths.

 

E.    From Buildings, Bridges and Other Structures.

Conductors shall be so arranged as to hamper and endanger fireman as little as possible in the performance of their duties.  The requirements of Table 1, Case 8, apply also to fire escapes, exits, windows, etc., at which human contact may be expected.  Where the vertical distance of a conductor, above ground, is in excess of 35 feet, this clearance may be reduced to 4 feet for circuits of less than 7500 volts.  (See Rule 54.8-A6.)

Where attached to the surface of buildings, the installation shall be made in accordance with the electrical safety orders of the Industrial Accident Commission.

 

F.    From Guys and Messengers (see Table 2 Column A, Rule 56.4-A)

 

G.    From Cross Arms.

The minimum distances of wires from the surface of crossarms are given in Table 1, Case 9.  These requirements do not apply at points of entrance to cut outs, switches, etc.  (See Rule 58.4-D for lead wires.)

 

H.    From Drip Loops.  (See Rule 54.6-A)

The lowest point of the drip loop from the terminal or end of a conduit run shall have at least a minimum vertical separation of one foot from the nearest supply conductor level below it.

The lowest point of the drip loop (750-7500 volts) from a transformer shall not be less than 18 inches vertically above conductors of 0-750 volts supported on transformer heel arms.
  (See Rule 58.4.)

 

I.    From Grounded Metal Fittings.

All grounded metal fittings installed on wood poles or structures shall obtain at least a 6 foot vertical separation below open wire conductors.  Should it be impracticable to maintain such vertical clearance, a reduction to 4 feet below conductors, excepting messengers dead-ended to poles below open wire conductors of 750-7500 volts, will be permitted, provided a suitable protective covering or guard is used.

 

J.    From Hardware.

Risers and vertical runs of wire or conduit shall not contact guys, bolts or other metal members of a pole or structure (other than of iron or steel) which can not be protected with a suitable protective covering unless such contact is specifically made more than 8 feet below the lowest conductor upon the pole.