This part of EN 61643 is applicable to devices for surge protection against indirect and
direct effects of lightning or other transient overvoltages. These devices are called
Surge Protective Devices (SPD). These devices are designed to be connected to
50 Hz a.c. power circuits, and equipment rated up to 1 000 V r.m.s. Performance
characteristics, safety requirements, standard methods for testing and ratings are
established. These devices contain at least one nonlinear component and are intended
to limit surge voltages and divert surge currents.