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Choosing varistor that matches fuse.

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Jstrahan

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Im currently working on a inverter driverboard that got caught in a bad power surge. The fuse is rated at 8amp/125vac. The varistor is completely burnt up so i cannot identify it. Should i base the varistor on the fuse since they are in series? The varistor will go line to neutral.
 

Varistor should be selected according to nominal line voltage, e.g. 130 or 140Vrms for 115V grid. Power respectively size as before, or larger if possible.

The fuse can't actually protect the varistor in case of a long enduring surge.
 

So if my rms is 130v is that what my working voltage should be for the varistor or the clamping voltage?
 

Hi,

working voltage (= normal operating voltage, nominal line voltage)


Klaus
 

So let me get this straight. My mov should be slightly higher than the rms? What confuses me is the fact that some posts state that on a 115-120vac circuit i should have a varistor whos working voltage should be 170. Im going crazy.
 

We have regularly 275 Vrms varistors for 230 V grid voltage, so I would rather suggest 140 Vrms.
 

Thanks for all the replys. One last question... what is the difference between varistor voltage and maximum allowable voltage? For example the is another varistor in my circuit that has a varistor voltage of 270 l, but the maximum allowable vac is 175. The only difference between this one and the one i'm replacing is that one is Line to Neutral(replacing) and the other is Line to Ground.
 

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