Self-regulating electrical strip heaters which comprise at least two elongate conductors and at least one elongate resistive heating strip which contacts the conductors alternately as it progresses down the length of the heater. The conductors can be separated from each other by an insulating strip,...http://www.google.co.uk/patents/US4459473?utm_source=gb-gplus-sharePatent US4459473 - Self-regulating heaters
