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Metal Oxide Varistor

By on August 28, 2007

 metal oxide varistor

Metal Oxide Varistor (MOV) are voltage  dependent symmetrical resistors intended to protect equipment from transient voltages resulting from lightning strikes. This component is located near the ac supply input and before the bridge rectifier. The use of MOV not only reduces the chance of electrical damage buut also improves equipment reliability. Metal oxide varistor have many types of colors and to test it you can use an analog meter set to X 10 K ohm and it should show no reading on both ways. If you got any readings then it had developed a short circuit.

Some important parameters of MOV are a varistor’s energy rating (in joules), response time (how long it takes the varistor to break down), maximum current and a well-defined breakdown (clamping) voltage. The energy rating is often defined using ‘industry standard’ transients such as 8/20 microseconds or 10/1000 microseconds. Metal Oxide Varistor are designed for shunting short duration pulses. For example, 8 microseconds is a transient’s rise time; 20 microseconds is the fall time. If it break down get back the same spec or some closer value.

zinc oxide varistor



  1. Bala

    July 29, 2011 at 12:23 am

    How to test MOV(metal oxide varistor) please help as well as soon

  2. admin

    July 30, 2011 at 12:46 am

    HI Bala,

    Set your analog meter to x 10k ohm and it should have no reading in either direction.


  3. Dimitrios

    January 10, 2012 at 11:00 pm

    Dear Jestin,
    Please advise me how can i test a varistor "SV03YS". This varistor is silicon symetrical type an looks-like as diode with cathode mark and loacated in an AVR unit (power supply).
    I downloaded the datasheet of related varistor and the internal juction shows "3 diodes in series" connection.
    Or advise me what is the equivalnet? in order to replace it. I susspect that is defective, but i'm not sure.
    For your info while the AVR is at good working condition, at the anode applied 28vdc and at the cathode 42vdc, in accordance of service manual.

    Best regards in advance for your kind assistance.

    • stu

      May 8, 2017 at 3:42 am

      Those kenwood avr units are touchy and badly designed, good luck with it.

  4. admin

    January 12, 2012 at 8:12 pm

    Hi Dimitris,

    I'm not sure about this kind of varistor. For a normal varistor you can use analog meter set to x 10 k ohm and test it either way and it should not have reading. If have readings mean the varistor is shorted.


  5. Electrika

    October 26, 2014 at 4:23 pm

    What is the significant of different sizes of varistor?


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