Strength Requirements for All Classes of
(1) Wood: Wood crossarms shall be of suitable grades of Douglas fir, southern yellow 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 can be of any corrosion-resisting metal or alloy.
B. Minimum Size
(1) Wood: Crossarms used to support or guard supply conductors shall have cross-sectional dimensions not less than the following:
One piece (homogeneous): 3 ¼ x 4 ¼ inches
Fabricated: any single member, 1 ¾ x 4 ¼ inches,
Laminated: 3 x 4 inches.
Cross arms supporting or guarding communication conductors shall provide the strength of Douglas fir having a cross section not less than 3 by 4 ½ inches except that crossarms six and one half feet or less in length which support sixteen wires or less shall provide the strength of Douglas fir having a cross section not less than 2 ¾ inches by 3 ¾ inches.
(2) Metal: The physical properties as a result of dimensions, shape and cross-sectional area of metal crossarms shall be such as to result in sufficient strength to meet the requirements of Rules 46, 47, and 48.2, provided the thickness of any element shall not be less than 3/32 inch.
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.
Longitudinal Loads Normally Unbalanced:
Where crossarms are subjected to unbalanced longitudinal loads they 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 conductors are supported on pins and insulators, double crossarms shall be used to permit conductor fastenings at two insulators and thus retard slipping.
For conductors tensions up to 2000 pounds per conductor, double pins with 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.
D. Replacements (see Rule 44.2)