<P> Sometimes special circuits built for purpose of sensing the temperature or voltage status, and thereafter controlling these variables . In these circuits, Thermistors (Temperature dependent resistors), VDR (voltage - dependent resistors), thermostat (that switches off the circuit at higher - temperature), Sensors (such as infrared - thermometers), etc. used to modify the current upon different conditions like circuit - temperature and input voltage . </P> <P> For a certain definite purpose in a definite electrical equipment or a portion of it, definite type and size of materials (for boards, wires, insulators) with proper rating for voltage, current and temperature, are used . The circuit - resistance never kept too - low . Sometimes some parts placed inside the board and box, maintaining a proper distance from each - other, to avoid heat - damage and short - circuit - damage . To prevent short - circuit, on the wire - joints, appropriate type of electrical connectors and mechanical fasteners used . </P>

Electric circuits are protected from overheating by means of