The Siemens 4EU3921-0BE00-0A is a commutating choke (line reactor) designed for use with power converters — specifically a 3-phase choke rated for 380 V AC at 50 Hz. Its primary job is to limit the rate of current rise (di/dt) and smooth commutation notches on the converter's input or DC link, protecting the semiconductor bridge from excessive switching stress. Rated at 342 A continuous with a maximum of 380 A. The 0.00014 H inductance at 50 Hz with a 7.5% relative inductive voltage drop. At DC the rated current climbs to 465.6 A.
This is an open-frame (IP00) component — no enclosure, no finger-safe shrouding. The flat-type terminals (flat connector) on the main current circuit are designed for bus-bar or large-lug connections, not DIN-rail terminal blocks. Physical footprint: 0.41 m wide × 0.385 m tall × 0.229 m deep. Total power loss is 434 W in the coil plus 186 W in the iron core. Thermal class H (180 °C) winding insulation per IEC 60085 means the choke can run hot without degrading the magnet wire — appropriate for the 40 °C ambient rating and the high copper losses.
The 342 A rated current at 380 V AC drives the conductor sizing and the upstream protective device. This is not a 380 A part for continuous duty — the 380 A is the maximum (short-term overload), while 342 A is the continuous design point. A converter pulling 342 A RMS line current needs a choke this size; a smaller converter with a lower line current could use a lighter, cheaper reactor. The 7.5% inductive voltage drop means at rated current the choke drops voltage across its impedance.