The Siemens 4EU3921-0BC00-1B is a three-phase commutating choke (line reactor) designed for converter applications. It limits the rate of rise of current (di/dt) and reduces harmonic distortion on the line side of a variable-frequency drive or DC drive converter. Rated at 495 A continuous with a 550 A maximum at 50 Hz, it handles the full-load current of a substantial drive system — think 250–300 kW motor loads on 400 V AC three-phase. The 0.08 mH inductance (80 µH) and 6.4% relative inductive voltage drop (uk) are sized for typical drive input filtering. The 550 W coil loss and 170 W iron core loss at rated load tell you the thermal budget: this is a 720 W total dissipation component that needs free air or forced ventilation — IP00 means no enclosure, so it mounts inside a cabinet with clearance for airflow.
That 550 A maximum (Ithmax) is the short-time thermal withstand — not a continuous rating. For a drive with a 400 A output rating, this choke gives headroom; for a 500 A drive, you are at the limit and should verify the drive's input current profile. The 674 A DC rated value means this choke can also sit on the DC link of a converter, not just the AC line side. That is unusual for a commutating choke — most are AC-only. If you are retrofitting a DC drive bus, this single component covers both roles. Flat-type terminals (bus-bar style) on the main circuit mean you are landing lugged cable or bus bar, not wire ferrules. Plan for M8 or M10 bolt-down connections rated for 500 A class. The 0.229 m depth, 0.41 m width, and 0.385 m height define the cabinet footprint — allow 50 mm clearance on all sides for airflow and terminal access.