The reinforcement or armor is a cable protection against mechanical stress such as tensile loads and compressive loads, against external effects such as moisture and temperature, and against chemical substances and rodents.
Reinforcement is often placed under the cable sheath. For electrical cables, the protection can be metallic and non-metallic.
Metallic reinforcement is a corrugated steel sheath made of steel wires, and non-metallic is a glass yarn covering. Reinforcement with corrugated steel sheathing also offers the advantages of increased transverse compressive strength and transverse water tightness. FO cables with steel reinforcement are somewhat critical in that clean potential isolation of the steel jacket must be provided. The regulations for grounding such reinforcement are laid down in DIN 0800.