General Order 95
Detailed Construction Requirements for Supply Lines
(Class H, L and T Circuits)
Basic minimum clearances for messengers and insulated cables are specified in Rules 37 and 38 , Tables 1 and 2 respectively and shall be measured to the nearest surfaces of the cable and messenger assembly, including cable rings and messenger supports. The basic clearances specified for conductors, as modified by provisions of Rule 54.4 are applicable to insulated cables. These clearances for messengers and cables are also subject to the following modifications. The clearances required for supply conductors of 0 - 750 volts shall be applied to suitably insulated cables of any voltage having a metallic sheath which is bonded and grounded as specified in Rule 57.8 .
A. Above Ground
(1) Messengers and Insulated Cables: The basic clearances specified
in Rule 37
, Table 1
for conductors, as modified by provisions of
, are applicable to messengers and insulated cables (See
(2) Grounded and Bonded Messengers and Insulated Cables: The basic clearances
specified in Rule 37
, Table 1, Column D
, are applicable to grounded cables having metallic sheaths, and to effectively
grounded messengers (see Rule 57.8
Note: Revised January 21, 1992, by
B. Above Railways and Trolley
(1) Which Transport Freight Cars: The clearances specified in
Table 1, Case 1, Columns A, B, and D
are based upon the maximum height of standard freight cars, 15 feet 1 inch
from the top of rail to top of running board. These clearances shall in no
case be reduced more than 5% because of temperature, wind or mechanical loading.
(2) Operated by Overhead Trolley: The clearances specified in
Table 1, Case 2, Columns A and D
, 26 feet and 27 feet respectively, are based upon a maximum trolley pole
throw of 26 feet, the usual maximum height of a free trolley pole above the
top of rails or surface of streets used by trolley cars or coaches.
EXCEPTION: Messengers, and cables,
which are bonded and grounded as specified in
, may have clearances above the rails or surface of streets used by trolley
cars or coaches less than the distance specified in
Table 1, Case 2, Columns A and D
for trolley–throw clearance, provided the messengers and cables are not
less than 4 feet above the trolley contact conductor and are encased in
wood boxing or moulding with a minimum thickness of 7/8 inch (or other suitable
material having the same minimum electrical insulating qualities and mechanical
strength) for distances of at least 2 feet horizontally from the vertical
plane through each trolley contact conductor.
Note: Revised January
21, 1992, by Resolution SU–10.
C. Between Conductors
No specified clearance is required between the individual conductors of suitably insulated cables, whether single or grouped, and therefore the clearances specified in Table 2, Cases 15, 16 and 17 do not apply between such conductors. Any such multiple–conductor group shall be treated as a single conductor in the application of other clearance requirements.
Cables and Messengers
Cables supported by messengers are not required to be any specified distance from their supporting messengers.
The clearance specified in Table 2, Case 1, Column A does not apply and no clearance is required where messengers of the same electrical system branch or cross.
From Poles, Crossarms and Other Conductors
Messengers, and metal sheathed cables, which are bonded and grounded as specified in Rule 57.8 shall have clearances not less than the minimum clearances required for conductors of 0 - 750 volts with all of the following provisions being applicable:
(1) Attached to Surfaces of Poles and Crossarms: Such grounded messengers
and cables may be attached to the surfaces of poles or crossarms at less than
the clearance specified in Table
1, Column D, Cases 8 and 9
. When attached to pole or crossarm at less than 15 inches from centerline
of pole such grounded messenger or cable shall not be less than 4 feet vertically
above or 6 feet vertically below any unprotected supply conductor except
that where a guard arm (or arms) is placed above messenger and cable as specified
in Rule 57.7
, the clearance of 6 feet may be reduced to not less than 4 feet below unprotected
conductors of 0 - 750 volts (see
Figure 57–1 A
(2) Supported on Same Crossarm above 750 Volts: Such grounded messenger
and cable when supported on the same crossarm with unprotected conductors
in excess of 750 volts shall be placed on the side of pole opposite the unprotected
Figure 57–1 B
(3) Supported on Same Crossarm 0 - 750 Volts: Such grounded messenger and
cable when supported on the same crossarm with unprotected conductors of 0
- 750 volts, shall be placed at not less than pin spacing (
Table 2, Case 15, Column D
) beyond the outermost unprotected conductor on the same side of pole (see
Figure 57–1 C
(4) Between Cable and Unprotected Conductors: The clearances between
a cable and unprotected conductors shall not be held to apply between a grounded
cable (and its messenger) and unprotected conductors of the same circuit
on poles where unprotected conductors enter (or leave) a cable. On such poles
no grounded section of messenger or cable shall be less than 15 inches from
surface of pole.
(5) Two or More Cables Attached to the Surface of Pole: Where two or
more cables are attached to the surface of the same wood pole they shall
be placed on the same side of pole when their vertical separation is less
than 8 feet but in no case shall the vertical separation be less than 1 foot.
Note: Revised January 21, 1992, by Resolution SU–10.
G. From Buildings and Other Structures
Messengers, and metal sheathed cables, which are bonded and grounded as specified in Rule 57.8 are not required to clear buildings and other structures any specified horizontal distance and the clearance specified in Table 1, Case 7, Column D does not apply in such instances. Such cables, and messengers, shall be installed so that they do not interfere with the free use of fire escapes, exits, etc., and should be arranged so as not to hamper or endanger workers and firefighters while performing their duties.
Note: Revised January 21, 1992, by Resolution
H. From Nonclimbable Street Lighting or Traffic Signal
Poles or Standards
Messengers and metal–sheathed cables which are bonded and grounded as specified in Rule 57.8 , passing (unattached) nonclimbable street lighting and traffic signal poles or standards, including mastarms, brackets, and lighting fixtures may have a clearance less than the 36 inches specified in Table 1, Case 10, Column D , but shall have a clearance of not less than 15 inches, except when the conductors are mechanically protected from abrasion by materials specified in Rule 22.8 . Such mechanical protections shall extend not less than 15 inches in each direction along the cable from centerline of pole, standard, attaching mastarm or fixture, whether passing above, below or alongside. The conductors shall be installed in such a manner so as not to interfere with light distribution from lighting fixtures and shall not hamper workmen changing lamps or maintaining equipment.
Note: Added January 8, 1980 by Decision No. 91186 and revised March 9, 1988 by Resolution E–3076.