Abstract: An elongate heater (1) in which a resistive heating element core is surrounded by a first insulating jacket (9) and a second insulating jacket (11). In a preferred embodiment the resistive heating element core comprises a conductive polymer composition (3) and the heater passes the VW-1 flame test. The second insulating jacket (11) may be made from the same material as the first insulating jacket (9). For some applications it is preferred that the second insulating jacket be a thin film, e.g. polyester film.

Abstract: A melt-extrudable conductive polymer composition which contains a polymer, a particulate conductive filler, and a particulate nonconductive filler. When a standard strip heater is made from the composition and tested in a UL VW-1 test, it has comparable performance to a heater made from a second composition which is the same as the composition but which does not contain the nonconductive filler. When tested in a standard arcing fault test, the standard heater will trip a fuse in less time than is required by the second heater, i.e. in less than 30 seconds. In some embodiments, the composition also comprises a flame retardant, preferably a halogenated flame retardant. When strip heaters prepared from these compositions are tested in a standard arc propagation test, an arc will not propagate. A preferred nonconductive filler is Sb.sub.2 O.sub.3.

Abstract: An electrical device, particularly a self-regulating strip heater, has improved thermal efficiency, good mechanical properties, and acceptable resistance to water penetration when an outer insulating layer is applied in a way that it penetrates the interstices of a braid surrounding the heater. Appropriate penetration may be achieved by pressure-extruding the outer jacket over the braid.

Abstract: An electrical device, particularly a self-regulating strip heater, has improved thermal efficiency, good mechanical properties, and acceptable resistance to water penetration when an outer insulating layer is applied in a way that it penetrates the interstices of a braid surrounding the heater. Appropriate penetration may be achieved by pressure-extruding the outer jacket over the braid.

Abstract: A number of improvements to electrical devices, particularly sheet heaters, comprising conductive polymer compositions, are provided. The preferred heater has the following features (a) it comprises a laminar resistive element and a plurality of electrodes which are so positioned that the predominant direction of current flow is parallel to the faces of the laminar element, (b) it comprises a laminar insulating element adjacent to but not secured to the electrodes and the resistive element; (c) it comprises a metallic foil, which acts as a ground plane and is positioned adjacent the insulating element but is not secured thereto; (d) it comprises a dielectric layer intimately bonded to the resistive element and to the electrodes.The invention also provides an electrical device comprising first and second members having different resistivities, and a thin contact layer of intermediate resistivity positioned between the first and second members.

Abstract: A number of improvements to electrical devices, particularly sheet heaters, comprising conductive polymer compositions, are provided. The preferred heater has the following features (a) it comprises a laminar resistive element and a plurality of electrodes which are so positioned that the predominant direction of current flow is parallel to the faces of the laminar element, (b) it comprises a laminar insulating element adjacent to but not secured to the electrodes and the resistive element; (c) it comprises a metallic foil, which acts as a ground plane and is positioned adjacent the insulating element but is not secured thereto; (d) it comprises a dielectric layer intimately bonded to the resistive element and to the electrodes.The invention also provides an electrical device comprising first and second members having different resistivities, and a thin contact layer of intermediate resistivity positioned between the first and second members.

Abstract: A number of improvements to electrical devices, particularly sheet heaters, comprising conductive polymer compositions, are provided. The preferred heater has the following features (a) it comprises a laminar resistive element and a plurality of electrodes which are so positioned that the predominant direction of current flow is parallel to the faces of the laminar element, (b) it comprises a laminar insulating element adjacent to but not secured to the electrodes and the resistive element; (c) it comprises a metallic foil, which acts as a ground plane and is positioned adjacent the insulating element but is not secured thereto; (d) it comprises a dielectric layer intimately bonded to the resistive element and to the electrodes.The invention also provides an electrical device comprising first and second members having different resistivities, and a thin contact layer of intermediate resistivity positioned between the first and second members.

Abstract: A method and apparatus for converting a fluid tracing system, e.g., a thermally insulated steam heat tracing system for a substrate, into an electrical heat tracing system for the substrate. A typical steam tracing system includes a substrate to be heated; an interconnecting system of steam tracing tubes adjacent to and in thermal contact with the substrate; and thermal insulation surrounding the substrate and steam tracing tubes. The conversion method includes the steps of removing the thermal insulation at spaced-apart locations and opening up the plurality of interconnected tubes so that elongate electrical heating elements can be inserted into the tubes, inserting elongate electrical heating elements into the tubes, and connecting the elongate electrical heating elements to a power supply in order to heat the substrate. Preferably, a gel-forming liquid is introduced into the elongate tubes and is converted into a gel within the tubes.

Abstract: A heater immersible in liquids such as water suitable for water beds and a method for producing the heater are disclosed. The heater includes two-spaced apart metallic electrodes interconnected by a conductive polymeric matrix. A water-impermable barrier completely surrounds the polymeric matrix. A jacket of plasticized polyvinyl chloride can be placed around the barrier. The barrier also prevents plasticizer from the polyvinyl chloride from penetrating and damaging the conductive polymeric matrix.