Introduction to NEMA Arresters

Welcome to the NEMA Medium and High Voltage Surge Arrester Section homepage. This website is offered as a service by NEMA and our member companies. The purpose of the website is to provide information to end-users on the general understanding, selection, and application of metal oxide varistor (MOV) type surge arrester protection.

Surge arresters are designed to protect valuable equipment from overvoltages on the power system network. Without surge protection the equipment insulation will suffer damage. The purpose of the surge arrester is to limit the voltage on the system while providing a low-resistance path to ground for the surge current. The information on this site applies to arresters applied on AC systems larger than 1 kV.

The surge arrester industry has evolved over the past 50 years. Advances have been made in both the level of surge protection provided as well as the incorporation of new safer housing materials and improved construction methods. This has been accomplished by the introduction of highly non-linear MOVs to limit surge voltages on protected equipment and the increased use of polymeric materials to provide longer service life and enhanced safety at the end of the product life cycle.

Surge arresters are generally characterized by their design features and the typical application. Today there are two primary design types: porcelain and polymer housings. Arresters are also classified by their application for use on distribution systems (Light Normal, Heavy duty) or in substations (Intermediate and Station). These types of arresters are generally used to protect system components from permanent damage.

Another common application for surge arresters is for transmission line protection. These arresters are used to enhance the power quality of the entire grid. If lightning causes a line insulator to experience an electrical flashover, the result will likely cause a substation breaker operation. This will disrupt the flow of power to a sizeable number of end users. Line Surge Arresters (LSAs) are used to protect the line insulation from surge induced flashover and to help prevent intermittent switching interruptions. This website features some powerful tools to analyze the reliability and cost enhancements resulting from the use of LSAs.

The workhorse of the industry from the 1930’s to the 1980’s was porcelain housed surge arresters using internal components of Silicon Carbide material in combination with internal spark gaps. These products offered reasonable surge protection but not at the same levels as todays MOV surge arresters. Additionally, at the time these arresters were being installed, system fault currents were low relative to the higher fault currents common today. This is especially true in substations. Today’s MOV surge arresters offer superior protection and much better pressure relief capability than their predecessors. This website also provides information on asset protection related to the replacement of these older technologies. is designed to make it easy to find the information you need:

  1. Arresters 101 – General Information
  2. MOV Arresters – Selection Attributes of Quality Products
  3. Line Arresters – Use of Arresters for Transmission Reliability Improvement
  4. Field Evaluation – Monitoring the condition of in-service products
  5. Asset Protection – Help to determine if a change-out program is in order

Useful Info

Make old arrester replacement a part of your preventative maintenance schedule in order to improve systems.