New silicon rubber cable insulation promises circuit integrity, in flaming environment

To provide an improved alternative to fluoropolymers and other halogenated materials used for insulation of most plenum cables, a project was undertaken to develop silicone elastomers which would meet Steiner Tunnel test criteria. Equally important, the project aimed to retain the long recognized ability of silicone elastomers to form a nonconductive ash when burned. The new material resulting from this project provides improved flame retardancy and lower smoke density, without sacrificing the best flame environment properties of earlier silicone rubbers. It does not melt, flow or drip, and burns to form a ceramic that clings to the conductors. This nonconductive ceramic has enough strength to remain in place during and after burning, thus providing insulation between adjacent conductors to assure circuit integrity.