Abstract: A parallel circuit heating tape (13) of the kind comprising two electrical power conductors (12,15) with low resistance relatively thin heating elements (16) between them which dissipate heat, the tape (13) comprising a temperature monitoring conductor (18,25) which extends alongside one of the power conductors (12,15), the temperature monitoring conductor (18,25) being separated from the one power conductor (18,25) by a substance (23,28) which insulates the two conductors (12,18; 15,25) from one another when the temperature is below a specified temperature or temperature within a transition temperature range, and provides a current path from one conductor (12,14) to the other (18,25) when the temperature is above the specified temperature or temperature within the transition temperature range.

Abstract: A temperature sensor in a heating tape includes first and second electrical conductors, a substance such as salt in electrical contact with each of the conductors, said substance having a significantly different electrical resistivity when the substance is at a temperature below a transition temperature range than when the substance is at a temperature above said transition temperature range.

Abstract: An electrically conductive silicone rubber composition having a positive, non-linear, temperature coefficient of resistance and which is substantially non-conductive at a temperature above a predetermined transition temperature, the composition comprising up to 25% based on total material weight of conducting carbon black, from 29% to 62% based on total material weight of at least one additive having a particle size between 0.005 microns and 100 microns, being compatible with the rubber, and having a melting point above the curing temperature of the rubber.

Abstract: An electrically impedant article comprising an electrode embedded in a polymeric body having dispersed therein electrically conducting carbon black in which the body around the electrode contains a lower percentage of conductive carbon black than do other regions of the body further away from the electrode, the carbon black in said region around the electrode being of higher conductivity than the carbon black in said other regions. The polymeric body preferably comprises a silicone rubber. The article can be a heating tape having a pair of spaced parallel electrodes and may have a positive non-linear temperature co-efficient of impedance.

Abstract: A heating tape comprising a pair of elongate electrodes embedded in a body of electrically conductive material wherein the highest current density in the effective current path between the electrodes as herein defined, is at a location spaced from and intermediate the electrodes.