64    Strength Requirements.  (See Sec. IV.)

Where steel supports or towers are used which are not capable of withstanding practically as great a stress longitudinally as transversely, anchor towers shall be placed at intervals not greater than 10 spans, which towers shall be able to withstand the combined longitudinal tension under the loading of Section IV of all conductors up to 10,000 pounds plus one-half the excess above 10,000 pounds.  (See also Rule 47.2.)