The Siemens 3RB1253-0FB30 is an overload relay rated 50-205 A for full motor protection, size S6, with a trip class range of 5-30 F. It supports continuous or individual mounting, main circuit busbar connection, and auxiliary screw terminals. The relay includes integrated ground fault detection, monostatic outputs, and an overload warning function, operating on DC 24 V control voltage.
The 50-205 A range covers a wide band of motor full-load currents — from a 15 kW motor on the low end up to roughly 110 kW at 400 V. The trip class 5-30 F lets you match the relay's thermal curve to the motor's starting profile: class 5 for fast-starting loads like pumps, class 30 for high-inertia loads like conveyors or crushers.