Varistors are widely used in power supplies, surge protectors, industrial equipment, and home appliances to protect circuits from lightning strikes and transient overvoltage events.
However, after absorbing excessive surge energy, a varistor may eventually fail. Knowing how to identify and handle a failed varistor can help prevent further equipment damage and improve system reliability.
1. Disconnect the Power Immediately
If a varistor failure is suspected, disconnect the power supply immediately to avoid short circuits, overheating, or additional damage to the circuit.
2. Check the Varistor for Visible Damage
Inspect the varistor for signs of failure, such as:
Cracks or physical damage
Bulging or deformation
Burn marks or discoloration
Charring around the component
If no visible damage is present, use a multimeter to check its resistance. A healthy varistor typically shows very high resistance. A very low resistance reading may indicate failure.
3. Replace the Varistor with the Correct Specification
Always replace a failed varistor with a component that has the same voltage rating, surge current capability, and package size to ensure proper protection performance.
4. Investigate the Root Cause
A failed varistor often indicates that the system has experienced severe surge events. Engineers should also evaluate:
Surge environment and protection level
Varistor voltage rating selection
Coordination with fuses, GDTs, or TVS devices
Grounding and PCB layout design
Varistors are sacrificial protection devices designed to absorb surge energy and protect critical electronics. At JEC (Dongguan Zhixu Electronics), we provide a full range of high-reliability metal oxide varistors for power supplies, industrial control, renewable energy, security systems, and consumer electronics applications.
Contact JEC for free samples and one-on-one engineering support.
Post time: Jun-30-2026