4NC current transformers can be used as accessories in the case of alternating currents I > 10 A. See "​Energy в†’ Power distribution (Low-Voltage) в†’ Low-Voltage Components в†’ SENTRON Protection, Switching, Measuring and Monitoring Devices в†’ Measuring Devices and Power Monitoring в†’ Measuring Devices в†’ Accessories в†’ 4NC Current Transformers for Measuring Purposes".