A metal oxide varistor is a commonly used component that protects heavy electronic devices from voltage surges. It also causes the machine to short circuit rather than cause damage to the machine. A metal oxide varistor is made by combining zinc oxide and metal oxides, such as manganese and cobalt.
Metal oxide varistors are typically placed between two metal plates that serve as electrodes. When it is produced, a metal oxide varistor is rated for a certain number of uses. If a device is shorted above the varistor's rating, the metal oxide can begin to deteriorate, making a replacement necessary.