Solid-state overload relay with ground-fault and thermistor protection
The Siemens 3RB1253-0FM00-0FM0 is a solid-state overload relay that integrates thermistor motor protection and ground-fault monitoring into a single device. It covers the 50-205 A AC range at 220-240 V 50/60 Hz, using an external summation current transformer for ground-fault detection. The relay provides two independent signal paths: 1 NO/1 NC for overcurrent/thermistor alarm and 1 NO/1 NC for ground fault, both monostable. This means a single unit handles motor overload, winding temperature (via PTC thermistor), and earth leakage — reducing panel wiring and component count compared to separate relays for each function.