- Varistors are actually voltage dependent resistors. These days the MOV or metal oxide varistors tend to be the most commonly encountered. Surge protection is definitely an application where they are generally used. Inside the most common kind of surge suppressor, a part known as a MOV, diverts the extra voltage. An MOV or metal oxide varistor forms a link between the powered line and the grounding line. These kinds of semiconductors have got a variable amount of resistance that's reliant on the level of voltage.