What it is and what it does
The Siemens 3RT2028-1AU00 is a SIRIUS S0-frame power contactor rated 34 A in AC-3 duty at 480 V — that's the motor-switching current, not the resistive-heater current. The AC-3 rating governs inductive motor loads: starting current, breaking under full load. For a 480 V three-phase motor, this contactor handles up to about 34 A locked-rotor and 34 A full-load break. Screw-type terminals on the magnet coil and main contacts; the auxiliary switch block comes built-in with 1 NO + 1 NC contact.
Mounting and panel fit
Mounts by screw or snap-on onto 35 mm DIN rail per DIN EN 60715. The mounting position is flexible: ±180° rotation on a vertical surface, plus ±22.5° tilt forward/backward. Clearance: 10 mm upward, 10 mm downward, 6 mm sideways. Overall dimensions 85 mm high × 45 mm wide × 97 mm deep — fits standard S0 panel cutouts. Stranded or solid wire from 1 to 10 mm² on the main terminals.
Auxiliary contact ratings
Built-in auxiliary contacts: at 24 V rated value 10 A, at 48 V rated value 2 A, at 110 V rated value 1 A, at 230 V rated value 5 hp, at 400 V rated value 3 A. The 24 V 10 A rating covers PLC or relay coil loads; the 5 hp at 230 V covers small motor contactor coils. Arcing time 10 ms at 50 Hz.
Operating conditions
Rated for -25 to +60 °C during operation, storage from -55 to +80 °C. Mechanical life typical 10 million operations. Switching frequency: up to 1000 cycles/h at AC-1, 750 cycles/h at AC-3, 250 cycles/h at AC-4.