Thyristor-based soft starter, 81 A at 40 °C — the thermal budget decides the real current
The 3RW4424-1BC36 is a SIRIUS soft starter using thyristors for voltage ramp starting — the core switching element handles the inrush without mechanical wear on the main contacts. An integrated bypass contactor closes after the start ramp, taking the thyristors out of the circuit during run mode — this cuts heat dissipation and lets the soft starter handle continuous loads without oversized heatsinks. Motor overload protection is built in, and the unit also provides intrinsic device protection against overtemperature — no separate overload relay or thermistor relay is needed for the starter itself.
Panel fit and wiring — screw fixing, box terminals, 270 mm depth
Mounting is by screw fixing (not DIN rail snap-on), with the unit sized 170 mm wide, 192 mm high, and 270 mm deep — the depth is the dimension to check when the enclosure back-panel clearance is tight. The mounting position allows vertical surface mounting with ±90° rotation and ±22.5° tilt forward/backward, so the panel layout can tilt the unit without derating. Main circuit connections use box terminals accepting 2x (4... 50 mm²) stranded or 2x (10... 1/0 AWG) using both clamping points. Clearance around the unit: 100 mm above, 75 mm below, 5 mm at the sides. Maximum motor cable length is 500 m — sufficient for most industrial motor runs, but long cable installations should check for reflected wave effects on the thyristor stack.
Inside-delta wiring and adjustable current limit — application flexibility
The soft starter supports inside-delta circuit wiring, which connects the thyristors in the delta legs of a six-wire motor. This reduces the current through each thyristor to 58 % of the line current, allowing the 81 A unit to start motors with a higher nominal current in delta configuration. Adjustable current limitation lets the user set the maximum start current as a multiple of the motor FLA — useful for applications where the supply transformer or generator has limited short-term capacity. Minimum load is 8 %, so the starter can handle lightly loaded motors without instability. Pollution degree 3 per IEC 60947-4-2 means it is rated for industrial environments with conductive dust or occasional condensation.
Fault display and external reset — local and remote diagnostics
A display on the unit shows fault codes locally — no HMI or software needed for first-level diagnostics. An external reset input allows remote clearing of faults from a PLC or pushbutton panel, which is standard for automated restart sequences.