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General Order 64-A


Section IV


Strength Requirements For All Classes Of Lines


49.2   Crossarms


A.    Material


(1)    Wood:  Wood crossarms shall be of fir, pine or other suitable wood.


(2)     Metal:  Metal crossarms shall be of galvanized iron or steel or other corrosion-resisting metal.


B.    Minimum Size


(1)    Wood:  The minimum cross section of cross arms used to support supply conductors shall be 3 by 4 inches.  Cross arms used to support communication conductors shall be of a size to provide the strength of fir under the following conditions:

Crossarms of six and one-half feet or less in length, supporting sixteen wires or less, shall have a minimum cross section of not less than 2 by 3 inches.

Crossarms over six and one-half feet in length, or crossarms supporting more than sixteen wires shall have a minimum cross section of not less than 3 by 4 inches.


(2)    Metal:  Crossarms shall be of such dimensions as will meet the strength requirements of wood crossarms.


C.    Strength

Crossarms shall have sufficient strength to meet the requirements of Rules 46 and 47 and, in addition, shall be securely supported, when necessary, by bracing to withstand the vertical loads impressed upon them and to prevent any decreases in the clearances specified in Section III which might be caused by the tipping of the arms.


(1)    Longitudinal Stresses:


a)    Normally Balanced: Where the longitudinal stresses are normally balanced, cross arms shall be capable of withstanding, as a minimum, a pull of 700 pounds, acting in the direction of the conductors and applied at the outer pin position.



b)    Unbalanced:  Where cross arms are subjected to unbalanced longitudinal stresses they shall have sufficient strength requirements with safety factors at least equal to those of Table 4.

At unbalanced corners and dead ends, in Grades A, B and 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 conductor tensions up to 2000 pounds per conductor, double wood crossarms fitted with spacing bolts, blocks, plates and pines or other similar approved equipment at each end will be considered as meeting the strength requirements of Rules 47.4 and 47.5.


D.    Bracing

Suitable bracing shall be employed where necessary and braces shall be securely attached to poles and cross arms by means of lag screws or through-bolts.  Metal braces shall be of galvanized iron or steel or other corrosion-resisting material.


E.    Replacements (see Rule 44.2)