All MOV-based protectors intended for long-term use should have an indicator that the protective components have failed, and this indication must be checked on a regular basis to ensure that protection is still functioning. It’s not there, therefore how do we know if it failed?
Answer:
https://en.wikipedia.org/wiki/Surge_protector#Metal_oxide_varistor
This is the source. This indication is not required for standard compliance, only for “Wikipedia compliance”.
That said, the AC iPurifier is fused and in case of a failed MOV it will disconnect from the mains and the indicators will be dark. Thus a “device failure” indication is implemented, that covers the MOV.
Further, the MOV protection in the AC iPurifier (and in power strips etc.) is a secondary (supplementary) protection intended to improve the protection for sensitive and high-value electronics. They are a “last-ditch” protection in case of a lightning strike or switching transients defeating the primary protection or passing some of the transients.
Primary means of surge protection are integrated into mains systems as a matter of standards.
