25 A AC-3 at 400 V — what that means for your motor circuit
The Siemens 3RA2120-4DE27-0BB4 is a SIRIUS direct online starter rated 25 A in AC-3 duty at 400 V, so it switches standard three-phase squirrel-cage induction motors up to that current — think 11 kW at 400 V, or 20 hp at 460/480 V. The AC-3 rating governs motor starting and plugging, not resistive heating; that's the number that decides whether the contactor survives repetitive inrush.
Panel fit — size S0, spring terminals, DIN or screw mount
This starter lives in the S0 frame — 45 mm wide, 243 mm tall, 107 mm deep — and mounts either by snapping onto a 35 mm DIN rail or with screws through the back. Clearance: 50 mm upward, 20 mm forward, 20 mm to the side, 10 mm downward, zero backward — plan your enclosure depth and gland plate layout around those numbers.
Coil and control — 24 VDC, no PROFIsafe or PROFINET on this variant
The coil is 24 VDC nominal, held in at that voltage. This order code carries no PROFIsafe or PROFINET IO protocol — it's a conventional hardwired starter, not a fieldbus slice. If your safety circuit needs a networked disconnect, you want the -4DE27-0BBx variant with the communication module; this one is for straightforward 24 VDC control from a PLC output or pushbutton station.