Patent ID: 8432657

Claim:
A protection apparatus of a load circuit that supplies, to a load, electric power outputted from a power supply and drives the load, the protection apparatus being for breaking the load circuit when an electric wire temperature of the load circuit has risen, comprising: a timer that counts an elapsed time; a current detection device that detects a current flowing through an electric wire on a downstream side thereof; a switch device that switches connection and breaking of the electric power to the load circuit; a temperature estimation device in which a pseudo-heat capacity smaller in value than a heat capacity of the electric wire for use in the load circuit and a pseudo-thermal resistance larger in value than a thermal resistance of the electric wire are set, the temperature estimation device having a pseudo-arithmetic expression in which the pseudo-heat capacity and the pseudo-thermal resistance are assigned to the heat capacity and the thermal resistance in an arithmetic expression for calculating the electric wire temperature from the heat capacity and thermal resistance of the electric wire, and estimating the electric wire temperature by using the pseudo-arithmetic expression based on a value of the current detected by the current detection device and on the elapsed time counted by the timer; and a breaking control device for breaking the switch device in a case where the electric wire temperature estimated by the temperature estimation device has reached an allowed temperature of the electric wire.