Rated current and thermal derating — the real-world limit
The 3RW4028-1TB05 is rated 38 A at 40 °C ambient. The minimum load is 20 % of the rated motor current — below that the soft starter may not trigger the bypass contactor reliably. Size the motor so its FLA sits between 20 % and 100 % of the 38 A ceiling at your panel ambient.
Integrated bypass and thyristor stack — what that means for heat
This unit has an integrated bypass contact system and uses thyristors for the ramp-up. Once the motor is at speed, the bypass closes and the thyristors are out of circuit — so the heat load in the panel drops to the bypass contactor's dissipation, not the full SCR conduction loss. That matters for the vertical mounting surface limits: without an additional fan, the unit allows +/-10° rotation; with a fan, +/-90° rotation and +/-22.5° tilt front-to-back. The bypass also means the soft starter doesn't need to dissipate SCR heat continuously during run — the enclosure stays cooler than a non-bypassed design at the same current.
Mounting, clearance, and panel fit
Required clearances: 60 mm above, 40 mm below, 15 mm at the sides. The 155 mm depth is the body only — allow extra for the screw terminals on the main circuit and the control circuit. Pollution degree 3 per IEC 60947-4-2 — suitable for industrial enclosures where conductive dust or occasional condensation is present.
Control voltage and wiring
Control supply is 24 V AC/DC at 50/60 Hz — the same 24 V rail that powers the PLC cabinet. Main circuit terminals are also screw-type. Maximum motor cable length is 300 m — beyond that, capacitive charging current from the cable can interfere with the thyristor gating. An external reset input is provided for remote restart after a fault trip.