Overvoltage

• overvoltages that arise from external sources and enter via the terminals, and
• overvoltages that are created in the actual equipment and occur at the terminals.

1. Equipment in overvoltage category I are only specified for use in equipment or parts of systems in which no overvoltages can occur, or are specifically protected against overvoltages, e.g. by overvoltage surge arresters, filters or capacitors.
   Note: The equipment in this overvoltage category is mainly operated using low voltages.
2. Equipment in overvoltage category II are only specified for use in equipment or parts of systems in which lightning surges do not have to be taken into account. (Overvoltages due to switching activities must be taken into account.)
3. Equipment in overvoltage category III are only specified for use in equipment or parts of systems in which lightning surges do not have to be taken into account (overvoltages due to switching activities must be taken into account) but, with respect to safety and availability of the equipment or networks that are dependent on it, are subject to special requirements.
   The overvoltages created by the equipment itself must not exceed the values of overvoltage category II.
   Note: This includes equipment for fixed installations, e.g. protective equipment, contactors, switches and sockets.
4. Equipment in overvoltage category IV is defined for use in equipment or parts of equipment in which lightning surges must be taken into account.
   The overvoltages created by the equipment itself must not exceed the values of overvoltage category II.
   Note 1: This includes equipment for connecting overhead lines, e.g. ripple control receivers, counting circuits.
   Note 2: If a cable network (laid below ground) supplies a building, it is sufficient to measure the equipment according to overvoltage category III.