What is a metal oxide varistor?
A metal oxide varistor is a voltage-dependent, semiconductor-based, variable resistor. Electrically, it appears as an open circuit across a power line until its voltage threshold is reached. When this occurs, the varistor will instantaneously change from a high resistance mode (open circuit) to a low resistance mode (short circuit), thus conducting currents through it. Once the overvoltage event has passed and the voltage returns to below the threshold level of the varistor, it will return to an open circuit again until the next overvoltage event that exceeds its threshold occurs.
