Trip class and motor protection timing
The 3RU2126-4CB1: If your motor has a long acceleration time (high-inertia fan or crusher), CLASS 10 may nuisance-trip on start; you'd need a CLASS 20 or 30 relay instead. The S0 frame size (97 mm high, 45 mm wide, 95 mm deep) fits the standard SIRIUS contactor footprint — it mounts directly below a 3RT2 contactor of the same size class without extra bracketing.
Auxiliary contact ratings across control voltages
These are the make/break capacities for the signal circuit — the 120 V rating is the highest current point, so if your PLC input module runs on 24 VDC, budget 2 A max per contact. At 60 V and 125 V the contact is rated 0.3 A and 0.22 A respectively — these lower values reflect DC switching limits where arc extinction is harder. For DC control circuits, verify the voltage matches the rating table.
Temperature compensation and mounting flexibility
Temperature compensation is active from -40 °C to +60 °C ambient — the bimetal element adjusts for ambient heat so the trip point stays accurate whether the panel is in a heated factory or an unheated warehouse. Operating range extends to -40 to +70 °C, but above 60 °C the compensation curve stops tracking.
The 3RU2126-4CB1 is the standard SIRIUS thermal overload relay in the S0 frame, not a phase-out or NRND variant. Substance prohibitance date of 10/01/2009 indicates RoHS compliance per Siemens' declaration. The relay carries the SIRIUS brand designation and is designed for the main current circuit with screw-type terminals.