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PlasmaSheep t1_ixy63lt wrote

Reply to comment by Xyspade in Not as old as a lot of the stuff on here, but a 6 plug wall adapter from RadioShack. Made November 20th, 1994. by 2XGSWsurvivor

Put simply, the MOV acts as an open circuit until the voltage across live/ground or neutral/ground exceeds a "clamping voltage". The MOV then presents almost no resistance, making most of the current flow through it rather than through the device under protection. It gets "used up" because passing current through the varistor affects its structure and increases its clamping voltage.

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Xyspade t1_ixzb2h1 wrote

Ah, thank you! So when the protection light goes out, that's its way of telling you the clamping voltage is too high to be useful anymore?

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PlasmaSheep t1_ixzy297 wrote

That's right.

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Xyspade t1_iy06psp wrote

Makes sense then why people say they should be replaced every few years regardless of whether the indicator is still lit or not. Learned a thing today!

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