The Siemens 4EU3951-7UB00-0A is a 3-phase mains choke (Netzdrossel f. FU) sized for the output of a frequency converter or the line side of a drive system. It carries a maximum continuous current of 1250 A and a rated current of 1125 A at 500 V AC, 50 Hz, with a rated inductance of 14 µH and a relative inductive voltage drop of 2 % at rated conditions. That 2 % drop is the design target — it limits harmonic distortion and di/dt stress on the drive's input rectifier without dropping so much voltage that the DC bus sags under load. The choke is wound for thermal class H (180 °C) insulation per IEC 60085, which means the winding can run hot without degrading the magnet wire varnish; the coil dissipates 540 W and the iron core another 192 W at full rating, so forced airflow or generous cabinet ventilation is expected — IP00 means no enclosure, so it must live inside a panel that provides the environmental seal.
The choke measures 0.41 m wide by 0.385 m tall by 0.229 m deep. Main circuit connections are flat-type terminals — expect busbar or heavy cable lugs, not screw-clamp wire terminals. This is a panel-mount component, not DIN-rail; it bolts into a drive cabinet, typically on a mounting plate near the line input or DC link. At 1125 A continuous, the buswork and fusing upstream need to match — do not undersize the branch circuit.
The 1250 A maximum and 1125 A rated current tell you this choke is built for a drive in the 560–710 kW range on 400 V or 500 V class (depending on drive efficiency and overload profile). The 2 % impedance is typical for a line reactor that filters harmonics without creating a significant voltage divider — at 2 %, the voltage drop at full load is about 10 V on a 500 V line, which most drives tolerate easily. The 50 Hz operating frequency is fixed; if your site runs 60 Hz, the choke will still work but the inductive reactance rises by 20 %, increasing the voltage drop to about 2.4 % — still acceptable for most applications, but check the drive's minimum line voltage spec. Thermal class H (180 °C) gives headroom for high-ambient cabinets or poorly ventilated installs, but the 732 W total loss (540 W coil + 192 W core) must be removed — plan for forced air or a derating if the cabinet ambient exceeds 40 °C.