Flame-resistant plenum cable and methods of making

A relatively low pair count cable which resists flame spread and smoke evolution, said cable comprising:

• a core which includes at least one conductor enclosed in a coating of polyvinyl chloride plastic material;
• and
• a sheath system which encloses said core and which has a relatively low thermal conductivity, said sheath system being effective to delay thermal decomposition of the conductor coating when the cable is subjected to a relatively high temperature and including;
• a layer of a woven glass material which is disposed loosely about said core to permit expansion of the plastic coating of the conductors when it is thermally decomposed, and which has a longitudinal overlapped seam, said layer of woven material being impregnated with a plastic material and having an air permeability which falls in the range of about 0 to 35 cfm and which is sufficiently low to minimize gaseous flow through said layer and to delay heat transfer to the core for a predetermined time;
• an extruded jacket of a fluoropolymer plastic material which encloses said layer of woven material;
• and
• a laminate interposed between said layer of impregnated woven material and said jacket, said laminate comprising a metallic foil which faces said layer of impregnated woven material and a layer of woven material which faces said jacket.

A method of making a fire retardant plenum cable, said method comprising the steps of:

• advancing a core comprising at least one conductor which is enclosed in a coating comprising a polyvinyl chloride composition along a path of travel;
• wrapping a relatively thin strip of woven glass material which is impregnated with a plastic material and which has a relatively low air permeability that falls in the range of about 0-35 cfm, and a relatively low thermal conductivity about said core without duly compressing said core to form a longitudinal overlapped seam;
• and
• extruding a layer of a fluoropolymer plastic material about the strip of woven glass material to form a jacket.

A method of making a fire retardant plenum cable, said method comprising the steps of:

• advancing a core comprising at least one conductor which is enclosed in a coating comprising a polyvinyl chloride composition along a path of travel;
• wrapping a strip of a woven glass material which has a relatively low air permeability, and a relatively low thermal conductivity about the core without unduly compressing the core to form a longitudinal overlapped seam, the woven glass material comprising a strip of woven glass material which has been impregnated with a fluorocarbon resin, the degree of impregnation of the woven glass material being increased as the number of conductors in the core increases;
• wrapping a laminate comprising a metallic foil and a layer of woven glass material about said layer of impregnated woven glass material;
• and
• extruding a layer of fluoropolymer plastic material about the laminate to form a jacket.