This circuit can sense the overload condition and breaks the power if the load increases above the set point. It is an ideal circuit to protect Uninterrupted Power Supply devices like Inverter.Let us see its working …The Optocoupler MCT2E and the Resistor R3 (1 Ohm 10 Watts) will do the trick. The Optocoupler has an LED and a Phototransistor inside with connecting leads. The LED of MCT2E is connected parallel to the resistor R3 with a current limiter R2 for the LED. The phototransistor of Optocoupler is connected to the transformer derived 9 volt DC through the current limiter R1. The load is connected through the Common and NC contacts of the relay. So it will work normally at power on.