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SPD Protection.

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I recently bought a 1 metre long two way 13 Amp trailing socket extension lead. It contains a varistor with a thermal fuse attached to its side, and two neon indicators. It is well made and clearly has been designed well. The varistor is connected to L. and N. The thermal fuse is held tightly on one side of the varistor disc. Neon light 1 indicates mains present. Neon light 2 indicates that the varistor is still in circuit and that the thermal fuse is still intact.

Total cost delivered= less than £9.00. Compare that cost with the units designed for permanent installations.

Varistor - Wikipedia

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    M.O.V. S.P.D. failure: a quote:

    “Cumulative degradation occurs as more surges happen. For historical reasons, many MOVs have been incorrectly specified allowing frequent swells to also degrade capacity.[13] In this condition the varistor is not visibly damaged and outwardly appears functional (no catastrophic failure), but it no longer offers protection.[14] Eventually, it proceeds into a shorted circuit condition as the energy discharges create a conductive channel through the oxides.”

     

    A 130 volt, 150 J MOV that has undergone catastrophic failure, apparently as a result of a lightning strike, showing evidence of heat and smoke. The 3 amp fast-blow fuse immediately in front of the varistor blew during the same event.

    A series connected thermal fuse is one solution to catastrophic MOV

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  • 0

    M.O.V. S.P.D. failure: a quote:

    “Cumulative degradation occurs as more surges happen. For historical reasons, many MOVs have been incorrectly specified allowing frequent swells to also degrade capacity.[13] In this condition the varistor is not visibly damaged and outwardly appears functional (no catastrophic failure), but it no longer offers protection.[14] Eventually, it proceeds into a shorted circuit condition as the energy discharges create a conductive channel through the oxides.”

     

    A 130 volt, 150 J MOV that has undergone catastrophic failure, apparently as a result of a lightning strike, showing evidence of heat and smoke. The 3 amp fast-blow fuse immediately in front of the varistor blew during the same event.

    A series connected thermal fuse is one solution to catastrophic MOV

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