A protective device for minimizing fire danger in the use of electrical circuits comprises a unit having a mechanically biased conductive element in series with the circuit, and maintained in position under tension by a fusible material such as a Cerro alloy having a yield point at a selected temperature threshold. When overheating at some other point in the circuit results rise of temperature at the protective device, the yielding of the fusible material allows the conductive element to spring free, opening the circuit and cutting off the current. This arrangement is useful in an male plug integral to or separate from an extension cord, in conjunction with circuit breaker systems, in a in-circuit device, and in electrical appliances and devices.