The Siemens 3RB1253-0FM20 is a solid-state overload relay from the SIRIUS family, Size S6, covering a 50-205 A adjustment range for full motor protection. The 50-205 A window means it directly protects motors with FLA in that band — not a wider range you can stretch, but a fixed span that must match the motor nameplate. The class 5-30 selection lets you tune the trip curve to the starting profile: class 5 for short-start loads like centrifugal pumps, class 10 for standard induction motors, class 20 for high-inertia fans, class 30 for crushers or conveyors with long acceleration. The AC 220-240 V, 50/60 Hz control supply powers the internal electronics and the ground-fault detection circuit, which signals a separate monostable output — not a built-in shunt trip, but a dry-contact signal you wire into the safety chain.
Deployment context — where this relay goes
This relay mounts on a Size S6 contactor or individually on a DIN rail. The main circuit uses busbar connection — no screw terminals on the power path, so the panel builder needs busbar jumpers or a pre-wired bus system. The auxiliary circuit uses screw terminals for the reset (manual/automatic/remote selectable) and the ground-fault signaling output. The integrated ground-fault detection is a differentiator: it monitors leakage to earth and triggers a separate output, which can drive a warning lamp or a PLC input without needing a separate ground-fault relay. That saves a DIN-rail slot and one wiring step in a motor control center.