Varistors, MOVs

About Varistors, MOVs

Varistors and metal-oxide varistors are voltage-dependent resistive components used to suppress transient overvoltage and divert surge current. Their resistance drops rapidly when the applied voltage exceeds a defined level, helping protect downstream circuitry from lightning-induced surges, switching transients, electrostatic events, and other voltage spikes. They are commonly used in AC mains inputs, power supplies, industrial controls, appliances, telecommunications equipment, automotive electronics, and renewable-energy systems.

Select a varistor by maximum continuous AC or DC working voltage, varistor voltage, clamping voltage, peak surge-current rating, pulse-energy rating, and transient waveform. The normal operating voltage must remain below the continuous rating, while the clamping level must protect the downstream circuit without nuisance conduction. Also compare capacitance, response time, leakage current, disc or SMD size, lead spacing, pulse lifetime and derating, operating temperature, agency approvals, and failure mode. For mains applications, coordinate the MOV with a fuse or thermal disconnect and verify insulation, fire-safety, and surge-standard requirements.