Heat responsive cable assembly

Claim 1

In combination with a fire alarm system having a voltage source, a heat responsive cable assembly comprising a single pair only of solid electrical conductors of relatively soft, deformable material helically twisted about each other, said conductors being connected to said fire alarm system voltage source, and a medium of heat sensitive electrical insulation normally between said conductors, said heat sensitive insulation being removed from between said conductors in response to a predetermined high temperature condition to expose said conductors for engagement with each other, said conductors normally being spaced from each other by a distance of approximately 0.003 inch and being helically twisted at least 35 turns per foot of axial length, said conductors having relatively high rates of thermal expansion such that they are significantly expanded when exposed to said predetermined high temperature condition to provide different helix angles between adjacent sections of said conductors and effect contact therebetween, both of said conductors having substantially the same rate of thermal expansion and said insulation gasing off at said predetermined high temperature condition to provide clean contact areas on each conductor.