The Siemens 4EU4321-0BM10-0A is a commutating choke (line reactor) designed for the DC link of a converter drive. Its job is to limit current rise rates and reduce harmonic distortion on the line side of a variable-frequency drive or DC drive system. Rated for a continuous 1387 A at 780 V AC, three-phase, 50 Hz, this is a substantial component sized for large industrial drives — think 500+ kW motor loads on pumps, conveyors, or extruders.
The 1387 A rated current is the continuous thermal limit at 40 °C ambient. That is the number you match to the drive's input current rating, not the motor's full-load amps. The 780 V AC operating voltage suits 690 V class drives common in European and Asian installations. The 2 % relative inductive voltage drop is the impedance at rated current and frequency — a standard value for commutating chokes that provides enough inductance to smooth commutation notches without excessive voltage drop under load. Inductance is 0.00002 H (20 µH). That is a low value for a choke this size, which is typical for a commutating choke — it only needs to handle the high-frequency switching edges, not the full line-frequency impedance. The DC rated current is 1699.7 A, reflecting the higher RMS content in the DC link versus the AC line side. Total power loss is 940 W (710 W coil + 230 W iron core). That heat must be managed: the IP00 open construction relies on forced air or cabinet ventilation. Thermal class H insulation allows a 180 °C hot-spot temperature, giving margin in a warm cabinet, but the 40 °C ambient rating is the design point — derate above that.
Physical integration and connections
Dimensions are 0.46 m wide × 0.435 m high × 0.265 m deep. This is a floor-mount or chassis-mount component, not a DIN-rail device. The main circuit connection uses flat-type terminals — expect busbar or large cable lugs. Plan for a minimum 1 m³ of clear space around it for airflow and access. The IP00 rating means no enclosure protection; it must live inside a cabinet or electrical room.