General Order 95
Section IV
Strength Requirements for All Classes of Lines
49.2
Crossarms
A. Material
(1) Wood: Wood crossarm shall be of suitable grades of Douglas fir, Southern Yellow pine or other accepted species.
(2) Metal: Metal crossarms shall be of structural steel, cast steel, or malleable cast iron, properly galvanized or otherwise protected to resist corrosion, or may be of any corrosion–resisting metal or alloy.
(3) Prestressed Concrete: Prestressed concrete crossarms may be used provided they are designed in accordance with Rule 48.3–B.
(4) Other Material: Other materials may be used for crossarms provided they comply with Rule 48.4
B. Minimum Size
The physical properties as a result of dimensions, shape
and cross–sectional area of crossarms shall be such as to result in sufficient
strength to meet the requirements of these Rules.
Note:
Part (3) added February 13,
1974 by Decision No. 82466 Revised January 21, 1992 by Resolution SU–10.
C. Strength
Crossarms shall be securely supported by bracing,
where necessary, to withstand unbalanced vertical loads and to prevent tipping
of any arm sufficiently to decrease clearances below the values specified
in Section III
. Such bracing shall be securely attached to poles and crossarms. Supports
in lieu of crossarms shall have means of resisting rotation in a vertical
plane about their attachment to poles or shall be supported by braces as
required for crossarms. Metal braces or attachments shall meet the requirements
of Rules 48.2
and 49.8
. In computing the strength requirements to meet vertical loads the effect
of such bracing may be considered.
(1)
Longitudinal Loads Normally Balanced
:
a)
Supply Lines: Where longitudinal loads are normally balanced, crossarms supporting
supply conductors shall have sufficient strength to withstand a load, applied
in the direction of the conductors at the outer pin position, of 700 pounds
with a safety factor of not less than unity.
b)
Communication Lines, Class C: Where longitudinal loads are normally
balanced, crossarms supporting Class C conductors shall have sufficient strength
to withstand a load, applied in the direction of the conductors at the outer
pin position, of 400 pounds with a safety factor of not less than unity.
(2) Longitudinal Loads Normally Unbalanced: Crossarms subjected to unbalanced
longitudinal loads shall have sufficient strength to meet the strength requirements
with safety factors at least equal to those specified in
Rule 44
.
At unbalanced corners
and dead ends in Grades “A”, “B” or “C” construction, where conductor tension
is held by cantilever strength of pin–type insulators and pins, double crossarms
shall be used to permit conductor fastenings at two insulators to prevent
slipping. In lieu of double crossarms and double insulators, single crossarms
may be used with single insulators and steel pins and prefabricated conductor
ties.
For conductor tensions up to 2,000 pounds per conductor, double wood crossarms
fitted with spacing devices at each end will be considered as meeting the
strength requirements of Rules 47.4
and 47.5
.
Note:
Revised March 9, 1988 by Resolution E–3076.
D. Replacements (See Rule 44.3 )
E. Guard Arm
Guard arms shall be made of wood or other suitable material not less than 48 inches in length and meeting the same insulating efficiency as Rule 22.8. Each guard arm and related pole attachments are required by Rule 46 to withstand vertical load of 200 pounds at either end.
Note: Added January 13, 2006 by Decision No. 05-01-030