Output reactor for VFD motor protection
The Siemens SIDAC 4EU2421-0AL00-0A is a 3-phase output reactor (choke) designed to sit between a variable-frequency drive and its motor. Its job is to limit the rate of voltage rise (dV/dt) and reduce peak voltages from the drive's PWM output, protecting motor winding insulation on longer cable runs or with older motors. Rated for 35 A maximum current at 50 Hz line frequency, with a switching frequency of 7.4 kHz — matching common IGBT drive outputs. Inductance is 1 mH per phase, which gives roughly 4.14 % voltage drop (UK%) at rated conditions — a typical figure for output reactors sized to suppress reflected-wave spikes without excessive voltage sag under load. The 31.5 A operational current rating (I LN) is the continuous current it can carry in normal service; the 35 A figure (ITHMAX) is the thermal maximum for sizing upstream protection.
Mounting and integration — open-frame chassis
IP00 protection class means this is an open-frame component — no enclosure, no touch protection. It mounts inside a panel or cabinet, not exposed to the environment. Dimensions are 0.22 m wide by 0.21 m tall by 0.13 m deep, so it needs a clear footprint on the backplate or chassis floor. Terminations are free cable endings (flying leads), not bus bars or terminal blocks — plan for a strain-relief point and a nearby terminal strip for the motor cable connection. Thermal class H insulation (IEC 60085) means the winding can handle a 180 °C hot-spot temperature — generous headroom for the 111 W total power loss (coil plus iron core) at 40 °C ambient. That loss figure is real heat dumped into the cabinet; factor it into your enclosure ventilation or forced-air cooling calculation, especially if the reactor shares a compartment with the drive.
Designed to EN 61558-2-20 (safety of transformers, reactors, and power supply units) and UL/CSA recognized — the description carries that explicitly. That means it meets North American and European safety standards for the reactor class. No RoHS or REACH statement in the record, but Siemens standard production for this series typically complies; verify against the manufacturer's declaration if your compliance audit requires it.