Patent ID: 8437110

Claim:
A protection apparatus of a load circuit, comprising: a timer configured to count an elapsed time of a current flowing through a load via an electric wire; a current detection unit configured to detect the current; a switch portion configured to switch supply and interruption of the current; a temperature estimation unit configured to estimate a temperature of the electric wire based on a pseudo-temperature arithmetic expression; and a breaking control unit configured to break the switch portion when the temperature estimated by the temperature estimation unit has reached an allowed temperature of the electric wire, wherein the pseudo-temperature arithmetic expression is set in such a manner that, in a temperature arithmetic expression of the electric wire, the temperature arithmetic expression using the elapsed time counted by the timer, the current detected by the current detection unit, and a heat capacity and conductor resistance of the electric wire, a pseudo-heat capacity smaller than the heat capacity of the electric wire is assigned to the heat capacity, and a pseudo-conductor resistance larger than the conductor resistance of the electric wire is assigned to the conductor resistance.