A protective circuit includes a first jack, a second jack, a first control unit, a detecting circuit, and a logic control circuit. The first jack is connected to a power supply, and includes a grounding wire and a live wire. The second jack is connected to a load, and includes a grounding wire and a live wire. The first control unit includes a first relay, the first relay is connected to the live wire of the first jack and the live wire of the second jack. The detecting circuit detects whether the grounding wire of the first jack is grounded, and outputs indication signals accordingly. The logic control circuit outputs a control signal to the first control unit according to the indication signals to turn on/off the first relay, for allowing the live wire of the first jack to be connected to/disconnected from the live wire of the second jack.