Can MOV voltage be measured nondestructively?

[larrymoencurly]

Or do you have to destroy them?

[redwire]

Re: Can MOV voltage be measured nondestructively?

MOV's are mushy and follow a log I vs log V curve, so values cover a wide range. There is no sharp knee like a zener diode, but you can estimate the voltage rating using a few mA's test current (limit).
It looks like the voltage rating is where the MOV starts to conduct 1mA DC. So for a 250V (RMS) MOV, that's around 350VDC +/-10%:

Example B60K250 (Fig. 12)
200V 1uA
250V 5uA
300V 30uA
400V 1mA
450V 100mA
500V 10A

so it's 400-500V before the 250V rated MOV really does anything

Source: EPCOS MOV SIOV_General.pdf

[japlytic]

Re: Can MOV voltage be measured nondestructively?

If you limit current appropriately, it could be possible.

[Longbow]

Re: Can MOV voltage be measured nondestructively?

Often, you may want to obtain a likely part number from an unmarked MOV. Using a current limiting resistor (as above) note the a.c. voltage at which the MOV begins to conduct. Reduce that a.c. voltage by the safety margin of your choice - 10 to 20 percent - and you will have the approx. a.c. working voltage of the MOV. The physical size of the MOV will give you a clue to the peak surge current handling capability, which is the other important spec for the part.

[severach]

Re: Can MOV voltage be measured nondestructively?

A DY294 Digital Transistor Tester / Semiconductor Tester should be able to test these. In capacitor mode it raises the voltage until the device breaks down. Some capacitor types are instantly destroyed at first breakdown but electrolytic are not. A MOV won't be destroyed at the limited current it puts out.