Abstract: A method of making a conductive polymer sheet in which a hollow conductive polymer extrudate is slit and flattened. The resulting sheet may have improved resistivity uniformity over conventionally extruded sheet. The sheet is useful in producing electrical devices such as heaters and circuit protection devices.

Abstract: Electrical systems, especially elongate heating systems, include means for monitoring circuit continuity and/or absence of ground faults. The systems comprise a switching device, e.g. a thermostat, as well as a circuit breaker. When the switching device is on, a relatively high current passes through the circuit and when it is off, little or no current passes through the circuit. In one embodiment, a small controlled residual current flows in the circuit even when the switching device is off, and a current-detecting device signals when a discontinuity causes the current to drop below the expected value for the residual current. In another embodiment, the switching device is placed so that the heater (or other electrical load) is at a positive potential with respect to ground even when the switching device is off, and a ground fault indicator is used to compare the currents in the two legs of the circuit and to signal when a ground fault causes the currents to differ.