The Siemens 4EU3951-1UB00-0A is a three-phase mains choke (line reactor) designed for installation ahead of a variable-frequency drive (FU). It smooths line-side harmonics and limits inrush current by presenting a 31 µH inductance at a 4% relative inductive voltage drop under rated conditions. Rated for 400/480 VAC at 50/60 Hz, it carries a maximum AC current of 910 A and a continuous rated current of 819 A. Total power loss sums to 730 W — 540 W in the coil and 190 W in the iron core — all dissipated into the surrounding air through the open IP00 frame. The 4% voltage drop figure is the key sizing parameter: it tells you the choke will drop 4% of line voltage at rated current and frequency, which is the standard impedance for most VFD line reactors. The 31 µH inductance value lets you verify coordination with the drive's DC-link capacitance.
Thermal class and enclosure
Insulation is Class H per IEC 60085, meaning the winding can sustain a 180 °C hot-spot temperature — a necessary margin for a 730 W loss device mounted in a warm cabinet. The IP00 rating means it is an open-frame component: no finger-safe cover, no drip shield. It must be installed inside a locked electrical enclosure with adequate ventilation or forced-air cooling. Dimensions are 0.385 m high by 0.41 m wide by 0.229 m deep. The main circuit connects via flat-type terminals (bus-bar or flat-cable lugs), not ring terminals or spring clamps — plan your bus-bar drill pattern and lug crimp tooling accordingly.