Abstract: A resistive element in the form of a bent metal plate is placed in a box-shaped case and has electrodes exposed out of the box-shaped case. A heat radiator in the form of a bent metal plate is also placed in the box-shaped case and has heat radiating electrodes exposed out of the box-shaped case. The resistive element and the heat radiator are held out of contact with each other and disposed in criss-cross relation to each other. The box-shaped case is filled with a cement material in surrounding relation to the resistive element and the heat radiator.

Abstract: A heater (10) for installation on a potable water tank (12). The heater (10) comprises a blanket (14) including an electrical resistance heating element (16) and a connection pad (18) for electrically connecting the heating element (16) to lead lines (20) to an aircraft power source (22). The water tank (12) is typically positioned under the cabin floor or other locations on an aircraft which are susceptible to cold temperatures, moisture invasion, and pressure drops/rises caused by changing altitudes. The heater (10) maintains the tank (12) at an acceptable temperature range and prevents freezing of the water.

Abstract: To reduce the tendency of ground faults and short circuits on electrical heating elements operating at elevated voltages and temperatures, resistance heating wire is coated with a sublayer of magnesium zirconate followed by an outer layer of aluminum oxide; each layer being in the range of 0.001 to 0.010 inches thick.

Abstract: An electrical heating element material of a sheet form is provided, which is comprised of a web of a synthetic resin having a plurality of metal conductor wires arranged therein in parallel to one another along the longitudinal direction of the web. The web is folded in succession at predetermined intervals along folding lines inclined at a small acute angle to the transverse direction of the web to form a substantially two-layer parallelogrammatic sheet. Considering the small angle, the sheet is, for practical purposes, rectangular.