RGU-100B is a Type B residual current protection and monitoring relay for WGB-series transformers. It measures AC, DC and mixed residual currents for loads with frequencies up to 2 kHz. Sensitivity is adjustable from 0.03 to 3 A with INS, SEL or 0.1 to 5 second delay. It includes a pre-alarm relay, event log, remote-control input, RS-485 Modbus/RTU communications and a high-contrast display that turns red on trip. The compact 3-module DIN-rail device is suitable for variable speed drives, UPS systems, photovoltaic installations, EV charging and active filters.