What it is and where it fits
The Siemens 3RB1036-1UB1 is a solid-state overload relay from the SIRIUS 3RB1 family, rated for motor protection in the 15 to 50 A range with Class 10 trip characteristics. It mounts individually (size S2) via screw connection and includes a built-on relay connector for auxiliary wiring. The manual-automatic reset selector lets the commissioning engineer choose between latching on fault or auto-reset after the thermal model cools — a decision that matters when the line is unattended overnight.
Key ratings and what they mean for fit
The 15 to 50 A setting range covers the most common motor FLA band for small-to-medium induction motors on 400 V three-phase supplies. Class 10 trip means the relay will open within 10 seconds at 7.2× the set current — fast enough to protect a standard squirrel-cage motor during a locked-rotor event without nuisance tripping on normal starts. The solid-state design means no bimetal fatigue and no ambient-temperature compensation drift over years of cycling, which is what makes this a reliable critical spare for a legacy panel.