Irregular voltage distribution is a very usual problem in power equipments that present a larger height. In arresters, it is characterized by the occurrence of larger voltage drops in the upper region of the equipment, close to the high voltage terminal. The level of irregularity in the voltage distribution depends on the geometry of the equipment and the used materials. The existence of earth capacitances is the main responsible for this problem. It is known, by means of tests and calculations that an increase of heating and leakage current in varistors present a straight relation with the level of earth capacitances in the arrester [8]. Pollution along the arrester housing is a problem that increases the voltage distribution irregularity, as though they create more intense earth capacitances. A simple solution to avoid this problem or reduce its effects is the application of grading rings. They allow a better voltage distribution along the arresters, reducing the effects of the earth capacitances. Another solution to avoid this problem is assembling the arrester with a larger concentration of varistors in the upper region so that there is a better performance where there is a larger voltage drop. Short-circuits in the inner region of the arrester are also a possible cause of voltage distribution irregularities in ZnO arresters.