The heart of many surge suppressors available today is a small electronic component called an MOV (Metal Oxide Varistor). 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.
Industry experts estimate surge probabilities in terms of thousands of surge occurrences. What do MOV manufacturers publish regarding their product’s surge capability?
This table shows three manufacturer’s surge ratings for two popular sizes of MOVs used in surge suppressors.
|Metal-Oxide Varistor Endurance Ratings|
|Panasonic||Siemens Components, Inc.||Harris Semiconductor|
|14mm MOV||10 surges of 1,000 amps||10 surges of 1,000 amps||10 surges of 1,000 amps|
|20mm MOV||100 surges of 1,000 amps||100 surges of 1,000 amps||100 surges of 1,000 amps|
A “best case” MOV rating is 100 surges – far under the high-performance, commercial standard of 1000!