Figure 4-12. - Crossarm.
of circuit protection devices and to support the conductors. The crossarms used in power distribution come in three common sizes; namely, 3 1/4 inches by 4 1/4 inches, 3 1/2 inches by 4 1/2 inches, and 3 3/4 inches by 4 3/4 inches. The spacing for insulators on the crossarms, as shown in figure 4-12, meets the minimum standards for conductors at all distribution voltages used by the Navy. In your naval service you may come across larger wooden crossarms or crossarms made of steel. These crossarms are designed to support increased strain or to use with transmission lines carrying higher voltages.
Single arms are used on straight lines when no excessive strain needs to be provided (fig. 4-13). When crossarms are installed, every other crossarm faces in the same direction.
A double arm should be used at line terminals, at corners, at angles, or at other points when there is an excessive strain (fig. 4-14). When lines cross telephone circuits or railroad crossings, double arms also should be used, as more than ordinary safety is required at such points. When two or more transformers are mounted on the same pole, double arms, as a rule, are used for their support.
Figure 4-13. - Single-arm construction.
Figure 4-14. - Double-arm construction.Continue Reading