Fire-Immune Cable

Abstract

A FACTORY, opened by Lord Ridley on October 12, for making fire-resist ing cable called 'Pyrotenax', marks a new development which promises to be of far-reaching importance to the electrical industry. The insulating cover utilizes a new insulating material, magnesium oxide, the heat-resisting and other physical properties of which have been proved in connexion with boiling-plate elements, which are made of resistance wire embedded in the oxide. 'Pyrotenax' cable has a copper conductor, magnesia insulation, and copper sheath. The new technique enables continuous runs of this cable up to 300 yards to be produced. A piece of cable in series with a burning lamp can be hammered to the thickness of a sixpence without affecting the light. It is therefore mechanically robust. For all practical purposes the cable is immune from fire and would not contribute anything to a possible conflagration. Notable use has been made of 'Pyrotenax' cable in France. The Louvre, the Norniandie, the Galeries Lafayette and the French railways use it. In Great Britain it has been adopted for the new lighting equipment of the Tate Gallery and for several industrial installations. The 'Pyrotenax' factory is practically 'all-electric' throughout, electric furnaces being used for all the annealing stages and for the dehydration of the magnesium oxide insulation. The rating of these furnaces is 250 kilowatts, and their temperature is controlled by a Cambridge thermostatic instrument. The factory is situated at Hedgely Road, Hebburn-on-Tyne. A full illustrated account appeared in the Electrical Times of October 21.