What circuit conditions does a metal oxide varistor protect against?

A metal oxide varistor (MOV) primarily protects against voltage transients and surges, such as those caused by lightning strikes, power surges, or electrical switching. It operates by clamping excessive voltage levels, thus diverting surge currents away from sensitive electronic components. This helps to prevent damage from overvoltage conditions, ensuring the safety and longevity of electrical devices. Additionally, MOVs can provide protection against transient overvoltages in AC and DC circuits.