Method of making high temperature parallel resistance pipe heater

Claim 1

The method of making a high-temperature parallel-resistance sheathed pipe heater cable capable of being operated at a temperature level of approximately 600° F on a sustained basis and capable of withstanding temporary occasional heating up to 1,000° F comprising the steps of providing a pair of flexible electrical conductors each including at least nineteen fine strands of nickel-clad copper wire, wrapping a primary layer of micaceous insulation around each of said conductors, braiding a secondary insulation layer of fiberglass threads tightly over said primary layer, said threads each being coated with an anti-fraying agent, stripping short sections of both primary and secondary insulation layers from said conductors at uniformly spaced intervals to expose bared segments of the conductors, each of said bared segments having the same predetermined length and being spaced from its neighbors by an interval of the same predetermined length, positioning said pair of stripped insulated conductors side-by-side with the bared segments of one being located mid-way between the bared segments of the other, twisting said pair of conductors together to form a twisted pair for holding the two conductors in position with the bared segments of one conductor alternating in occurrence with the bared segments of the other conductor along the twisted pair, helically wrapping a nickel-alloy resistance wire around said twisted pair of conductors with at least two bights of the resistance wire engaging each of said bared conductor segments for providing a multiplicity of contact points of high unit area pressure where each of said bights of the nickel-alloy resistance wire presses against the nickel-clad surfaces of the fine copper strands, wrapping another layer of micaceous insulation over said helically-wound resistance wire, braiding an outer jacket of fiberglass threads tightly over said latter micaceous insulation layer to form a jacketed heater cable assembly, and inserting said assembly into a stainless steel tube to form the sheathed heater cable.

Claim 2

The method of making a high-temperature parallel-resistance sheathed pipe heater cable capable of being operated at a temperature level of approximately 600° F on a sustained basis and capable of withstanding temporary occasional heating up to 1,000° F comprising the steps of providing a pair of flexible electrical conductors each including at least nineteen fine strands of nickel-clad copper wire, wrapping a primary layer of micaceous insulation around each of said conductors, braiding a secondary insulation layer of fiberglass threads tightly over said primary layer, said threads each being coated with an anti-fraying agent, stripping short sections of both primary and secondary insulation layers from said conductors at uniformly spaced intervals to expose bared segments of the conductors, each of said bared segments having the same predetermined length and being spaced from its neighbors by an interval of the same predetermined length, positioning said pair of stripped insulated conductors side-by-side with the bared segments of one being located mid-way between the bared segments of the other, twisting said pair of conductors together to form a twisted pair for holding the two conductors in position with the bared segments of one conductor alternating in occurrence with the bared segments of the other conductor along the twisted pair, helically wrapping a nickel-alloy resistance wire around said twisted pair of conductors with at least two bights of the resistance wire engaging each of said bared conductor segments for providing a multiplicity of contact points of high unit area pressure where each of said bights of the nickel-alloy resistance wire presses against the nickel-clad surfaces of the fine copper strands, wrapping another layer of micaceous insulation over said helically-wound resistance wire, braiding an outer jacket of fiberglass threads tightly over said latter micaceous insulation layer to form a jacketed heater cable assembly, and inserting said assembly into a stainless steel tube to form the sheathed heater cable.