The principal "active" element of the Surge Arrester is a metal oxide varistor characterized by high non-linearity. At a working voltage mainly a capacity current flows smaller than 1 mA. Any voltage increase causes a large increase of current flowing through the varistor, leading in turn to immediate limitation of further voltage increase on arrester terminals. When the over voltage disappears, the arrester immediately returns to its basic state.

Surge Arresters are equipped with a disconnecting device that disconnects the arrester from the network if it becomes damaged as the result of over voltage of too high energy or inadmissible voltage increase in the system. If such a situation occurs then the bottom terminal of the disconnecting device is "rejected" by the spring inside. This terminal remains suspended on an insulation "leash".

Kingtronics sell 2-Electrode arresters and 3-Electrode arresters. Following are 2-Electrode arresters and 3-Electrode arresters’s pictures.