photo of MOV

If a varistor falls on hard floor without any visual damage that can be seen after that, can it still be damaged inside?

Are varistors sensitive to that situation?

How can I do a simple test to check that the varistor didn't get damaged from the fall?


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    \$\begingroup\$ If it were a product going to NASA they would compute the impulse shock from epoxy hardness to get hundreds or thousands of g’s for xx to x us duration and determine if stress testing with vibration is needed or reject the product. Considering MOV’s have limited lifetime or number of surges, or accumulated Joules you may want to consider risk of field failure. Epoxy is very hard but metaloxide is very brittle crystalline structure. But wires are forgiving. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 12 '18 at 17:11
  • \$\begingroup\$ You says,that the metaloxide is very brittle,but wires are forgiving.What was your intention when you said,"wire are forgiving"?Did you mean that some ceramic zinc oxide grains may be damage,but it won't be critical? \$\endgroup\$ – xchcui Jun 13 '18 at 15:42
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    \$\begingroup\$ I meant if rare chance that leads landed 1st to reduce shock level , it may reduce risk. It may be OK depending on coating thickness. A spectrogram Sweep HV test on impedance will tell if grains shifted significantly ,as a non destructive fragility test compared to normal units up to 1MHz. Same test is done on GW size transformers after shipping. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 13 '18 at 15:55

Probably not, if the coating is not chipped.

If you read the datasheet you will find a voltage rating at which the current is guaranteed to be less than some nominal value (maybe 1mA). If you (briefly) apply the voltage and the current is less (typically it will be very much less) then the MOV is (most likely) functionally okay.

If the application requires very high reliability (eg. space or medical equipment) you may wish to discard a 50 cent part rather than bother, or use it for engineering samples and not items to be shipped.

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  • \$\begingroup\$ I can't achieved the right voltage in order to test the varistor,but i saw in the data sheet that each varistor has also a capacitance value.Can i test the varistor with a standard capacitor meter?Is it a reliable test to check the varistor? \$\endgroup\$ – xchcui Jun 13 '18 at 15:51
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    \$\begingroup\$ The concern would be an internal crack so I don't think the capacitance will be much of an indication. Really, it's probably fine. \$\endgroup\$ – Spehro Pefhany Jun 13 '18 at 16:22

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