This guide covers the application of metal-oxide surge arresters (see IEEE Std C62.11-1993 ) to safeguard electric power equipment against the hazards of abnormally high voltage surges of various origins. Such overvoltages may cause flashovers and serious damage to equipment and thereby jeopardize the supply of power to users. It is essential to prevent this by the proper coordination of surge-protective devices with the insulation strength of the protected equipment. This application guide does not cover the application of low-voltage surge protective devices below 1000 V ac. However, it references these devices when applied to the secondary of a transformer since they are part of the transformer protection. The subject is broad, with many ramifications, and it requires a volume of considerable bulk to explain all possible cases in detail. Clause of this guide covers the basic cases for stations used to supply and switch electric power transmission, subtransmission, or distribution feeders. Information is included in Clause on application of arresters for protection of overhead and underground distribution systems, all distribution transformers, and other electric distribution equipment. Step-by-step directions toward proper solutions for various applications are provided. In many cases, the prescribed steps are adequate. More complex and special situations requiring study by experienced engineers are described, but specific solutions may not be given. These procedures are based on theoretical studies, test results, and experience.