Patent ID: 8847605

Claim:
A connection diagnostic apparatus for a ground fault detector including an oscillator which generates a pulse signal and is connected via a coupling capacitor to an electric circuit with a first connection line for connecting a positive electrode of a power supply and a load and a second connection line for connecting a negative electrode of the power supply and the load, and a voltage detector for detecting a voltage value of the pulse signal between the oscillator and the coupling capacitor, comprising: a first relay provided in the first connection line; a second relay provided in the second connection line; and a programmable controller programmed to: turn on and off the first relay, determine that the ground fault detector is not normally connected to the electric circuit via the first relay if either a temporary voltaae decrease amount from a reference voltage value detected by the voltage detector when the first relay is turned on or a temporary voltage increase amount from the reference voltage value detected by the voltage detector when the first relay is turned off is smaller than apredetermined determination value, turn on and off the second relay, and determine that the ground fault detector is not normally connected to the electric circuit via the second relay if either a temporay voltage decrease amount from the reference voltage value detected by the voltage detector when the second relay is turned on or a temporary voltage increase amount from the reference voltage value detected by the voltage detector when the second relay is turned off is smaller than the predetermined determination value.