The heart of many surge protectors available today is a small electronic component called a metal oxide varistor (MOV). The role of the MOV is to divert surge current, however, MOVs wear out with use. As more surges are diverted, the MOV’s life span shortens, and failure becomes imminent. How soon? How many surges can they handle? No one knows until failure occurs! There is no forewarning or visual indications given – just failure. And while failing, they can reach very high temperatures, and actually start fires. See examples of catastrophic MOV failures in the photos below.