What should you do if an MOV burns out and cannot read voltage or resistance?

When dealing with a malfunctioning Metal Oxide Varistor (MOV) that has burned out, replacing it with a larger one is a prudent course of action. An MOV is designed to protect circuits from voltage spikes by clamping excess voltage to protect sensitive components. If the MOV has burned out, it likely indicates that the existing part was insufficient for the voltage or current conditions it faced.

Replacing it with a larger MOV means selecting one with a higher voltage rating or more robust specifications. This enhances the protection level of the circuit against future transient voltage spikes, which could otherwise cause additional damage. A larger and appropriately rated MOV can handle greater voltage and current without failing, thereby improving the reliability and safety of the system.

In contrast, using an older model may not have the necessary specifications to handle today's voltage requirements effectively. Attempting to reset the circuit without addressing the root cause of the problem could result in repeated failures, and ignoring the issue altogether poses a significant risk of damage to other circuit components. Therefore, opting for a larger MOV is the most effective way to ensure circuit safety and functionality.