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b. Sheath. A sheath is sometimes applied to the insulated conductors to provide extra protection from moisture, mechanical damage, or atmospheric contaminants. The sheath may be metallic armor, lead, or another protective covering. Wear at points of support and cracks from vibration are the princi­pal causes of sheath failure, although burns and mechanical damage are often contributing factors. Sheath repairs should be made as soon as the dam­age is discovered. If failure has not yet occurred, temporary repairs or protection may be desirable. Such temporary expedients may include providing

weather shielding, taping, or spreading single con­ductors. Permanent repairs should be as extensive as necessary, from patching to replacement of the damaged length.

c. Messenger. The supporting messenger is usu­ally of stranded galvanized steel or copper-clad steel. The initial design will provide adequate strength to support the cable under the maximum loading of ice and wind, and the temporary loads involved in installation and maintenance. Wear or rusting can reduce the messenger's strength. When it reaches the minimum safe value, then a messen­ger replacement should be made. Under these con­ditions, it is probable that other parts of the cable assembly will also require replacement.

d. Lashing. Metal rings are used with metallic-sheathed cables for field-assembled aerial cable. The disadvantage of this combination is the rela­tively rapid wear of the sheath at point of contact with the ring.

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