What It Is and What It Does
The Siemens 3RB1045-2EB0 is an electronic overload relay in the SIRIUS 3RB10 family, designed to protect three-phase motors against overload and phase imbalance. It mounts directly onto a matching contactor (size S3 footprint) and uses screw terminals for power and control wiring. The relay is set for Class 20 trip curve — meaning it allows up to 20 seconds of locked-rotor current before tripping, which suits standard motor starting profiles on pumps, fans, and conveyors. Reset is manual only, so the relay stays tripped until an operator physically presses the reset button, preventing automatic restart after a fault.
Key Ratings and What They Mean for Fit
The 25 to 100 A adjustment range covers a wide band of motor full-load currents — from a 7.5 kW motor on the low end up to about 45 kW at 400 V (assuming a typical 2.2 A/kW rule of thumb). The Class 20 curve is the standard choice for general-purpose induction motors; it coordinates with most IEC and NEMA motor thermal limits without nuisance tripping on startup inrush. The screw connection is a straightforward field termination — no special tooling beyond a screwdriver, and it accepts stranded or solid copper up to the terminal rating. Size S3 means the relay shares the mounting profile with S3 contactors (e.g., Siemens 3RT10 series), so it clips directly onto the contactor without extra DIN-rail space.