MOV (Metal Oxide Varistor) is an electronic component with a significant non-ohmic current–voltage characteristic.
MOVs are often used to protect circuits against excessive transient voltages by incorporating them into the circuit in such a way that, when triggered, they will shunt the current created by the high voltage away from the sensitive components.
A MOV’s function is to conduct significantly increased current when voltage is excessive. A MOV remains non-conductive as a shunt mode device during normal operation when voltage remains well below its “clamping voltage”. If a transient pulse (often measured in joules) is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed.
MOV introduces a “capacitor” like behavior in the circuit which makes then unusable in telecom or communication systems. MOVs are normally placed at the input of field input or power.
Every card is protected against surge and over-voltage through MOVs. MOVs are placed at the input field signals of DI and AI card. Protection against over-voltage in power line is achieve through a dedicated hot swap controller that cuts off the power when an over-voltage is detected.