S0 frame, Class 10 trip — the panel-fit facts
The 3RA2125-0KA23-0AK6 is a SIRIUS non-fused direct starter in the S0 frame size, rated 370 W at 400 V with a Class 10 thermal bimetallic overload relay. The S0 footprint means it occupies 45 mm on the DIN rail — one standard module slot — and needs 97.1 mm depth behind the gland plate, with 30 mm upwards and 10 mm forwards clearance for wiring and heat dissipation. The supplied contactor is a 3RT2023-1AK60, and the link module 3RA2921-1AA00 ties the contactor to the overload block; both are matched at the factory, so there is no separate ordering step for the interconnect.
Termination and mounting — what lands on the rail
Snap-on DIN rail or screw-mount with the additional push-in lug — the S0 base accepts both. The main contact terminals accept 1…10 mm² stranded, or 2x (2.5…6 mm²) for paralleled feeds; AWG equivalents are 2x (16…12) or 2x (14…8). That range covers the full motor branch circuit for a 0.5 hp load at 460/480 V or 575/600 V. Mounting position is vertical only, with pollution degree 3 — the enclosure seal and creepage distances are sized for conductive dust and humidity typical in industrial panels. Operating temperature range is -20…+60 °C, with storage from -50…+80 °C and transport down to -55 °C.