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As far as i know cumulative degradation occurs in a MOV when multiple surges appears in a circuit, A way to minimize this degradation is having multiple MOVs in parallel. This kind of damage can be internal and so not detectable by visual inspection.

In this situation i can use a digital multimeter to test the MOV for a short circuit between its terminals. I'm aware that this test is not 100% precise since a MOV can be damaged and present a open circuit between its terminals.

Taking MOV above its breakdown with a high voltage, to see if it conducts and check the clamp voltage does not seems very safe or practical.

My question is:

Beyond looking for short circuits between the terminals with a multimeter is there any practical way of testing a MOV (with no physical damage visible) in a PCB?

Thanks

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A MOV can be tested with a small applied current (such as 1mA) and that voltage compared with the datasheet specification.

For example, a Bourns MOV-07D221K should drop 198V minimum, 220V nominal 242V maximum at 1mA. That test should be done quickly with appropriate equipment to limit the current to avoid heating the MOV too much, particularly with higher voltage MOVs. Obviously, you would do that out of circuit.

Chances are if the MOV looks okay (and tests open circuit) it is, they normally fail shorted and only go open when they are blown open by excessive current (which tends to be detectable visually or by odor).

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    \$\begingroup\$ Having worked in the surge industry, 1.00mA from a wide range constant current source was a valid test the MOV manufacture approved of. Later on it became a UL test standard, before and after surge testing an MOV. +1 for accuracy. \$\endgroup\$ – Sparky256 Nov 17 '18 at 2:01
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    \$\begingroup\$ As a side note, MOV heating is related to watts dissipated, or the test current x the Vdrop of the MOV, so MOV's with a 1KV clamp voltage at 30mA would get very hot. At 1mA most all except tiny MOV's stay cool to the touch. \$\endgroup\$ – Sparky256 Nov 17 '18 at 2:05

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