Surge arresters are devices for protection of electrical equipment from over-voltage transients caused by atmospheric or internal switching events. Sometimes called a surge protection devices. They are designed to divert excessive voltages to ground and thus protect equipment in power transmission and distribution systems.

Many types of surge arrestors are available in both polymer and ceramic housing and for AC and DC applications. Typically designed to cover voltages from 6.6 kV to 1000 kV arresters protect distribution transformers, power equipment, cables and power station equipment. In special environments metal oxide varistors, also known as zinc oxide (ZnO) blocks, can be used inside GIS housing, pole mounted distribution transformers and power transformers. Prevailing standards governing this type of technology are IEC 60099-4 and IEEE C62.11.