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The positive temperature coefficient (PTC) generally defines a substance in which electrical resistance increases when temperature increases. In present usage, PTC refers to certain semiconductive thermistors which have significant positive temperature coefficients over a defined range of temperatures. PTC's have varied appliance applications, including temperature sensing, current controlling, and heating. Only the heat generating attributes of PTC's are considered. Design engineers are first provided with background information on the technical aspects of the PTC semiconductive pellet, which is the actual heat generating source. Also presented is information regarding the selection of the medium to transfer the heat. Then PTC heaters are analyzed with regard to their usefulness in certain appliance designs. A summary of the best PTC design attributes is also given.