This part of the IEC 61643 series is applicable to devices for surge protection against indirect and direct effects of lightning or other transient overvoltages. These devices are intended to be connected to DC power circuits and equipment rated up to 1 500 V DC Performance and safety requirements, tests and ratings are specified in this standard. These devices contain at least one nonlinear component and are intended to limit surge voltages and divert surge currents. The test requirements provided by this standard are based on the assumption that the SPD is connected to a DC power circuit fed by a power source providing a linear voltage-current characteristic. When the SPD is to be connected to a different kind of source, careful consideration is required. This mainly applies with regard to system and fault conditions to be expected in such a system (e.g. expected short circuit current, TOV-stresses). This standard can apply for railway applications, when related product standards do not exist for that area or for certain applications. Based on a risk assessment it may not be necessary to apply all requirements of this standard to SPDs designed for specific power applications only, e.g. circuits with a low power capability, circuits supplied by nonlinear sources, circuits with protective separation from the utility supply. NOTE 1: More information on risk assessment is provided in IEC Guide 116. SPDs for PV applications are not covered by this standard. NOTE 2: Such SPDs for PV applications are covered by IEC 61643-31. NOTE 3: Other exclusions based on national regulations are possible.