Flame retardant inside wiring cable with an annealed metal sheath

摘要

This specification describes an improved method for making fire-resistant communication cables that have a core which includes a multitude of individual conductors or pairs with insulation surrounding some or all of the conductors. The conductors are enclosed in a metal sheath that has a welded seam and that is annealed to maintain the flexibility of the cable. The sheath is of larger diameter of the core when welded, but is drawn down to a reduced diameter that hugs the core prior to the annealing. Heat insulation is wrapped around the core to protect the insulation on the conductors from the heat that is used to anneal the sheath. The purpose of the construction is to provide indoor cable that does not propagate flames from a burning area in a building into adjacent non-burning areas. The cable sheath is purposely not bonded to the core to facilitate sheath removal for ease of terminating the cable.