Question

Metal Oxide Varistors MOV's are non-ohmic variable resistors used in surge protectors to stunt away excessive currents in the event of a surge in the supplied voltage. How does an MOV work?

Answer 1

MOV is used with a fuse in parallel to the circuit that is to be protected.

When voltage (V) is within the rated limits, resistance (R) of MOV will be very high. So no current will flow through the branch with the MOV.

But when there is a voltage surge that goes beyond the rated limits, the resistance value of the MOV suddenly decreases to very low, as result of which, the entire large value of current will flow through the MOV, disconnecting the circuit to be protected from the path of the current flow. Again when the voltage comes down to the rated limits, the MOV will go back to its high resistance and the circuit will start functioning properly without getting damaged. So, MOV acts a surge protector.