748 A at 40 °C — what it means for your motor load
The 3RW4447-2BC34: That 40 °C rating is the standard panel ambient — above that, derate per the curve. For a 400 V motor drawing 680 A FLA, this soft starter has headroom at 40 °C but needs the 50 °C derating checked if the panel runs hot. Insulation voltage is 690 V rated value, so it comfortably covers 400 V, 480 V, and 575 V systems with margin. The pollution degree 3 rating per IEC 60947-4-2 means it's designed for industrial environments where conductive dust or condensation is present — the creepage distances are sized accordingly.
Inside-delta wiring — cuts phase current by 58%
This soft starter supports inside-delta circuit configuration, which connects the thyristors inside the motor delta winding rather than in the supply lines. That drops the current per phase to 58% of the line current — a 748 A line-rated unit handles roughly 430 A per phase in inside-delta mode. The main current circuit uses busbar connection with clamping points accepting 2/0 to 500 kcmil. The dimensions are 230 mm high, 210 mm wide, 298 mm deep — that depth is the dimension to watch in shallow enclosures. Clearance requirements: 100 mm above, 75 mm below, 5 mm at the sides.
Integral protection and adjustable starting
Motor overload protection is built in — no separate overload relay needed. The adjustable current limitation lets you set the starting current between 2x and 5x the motor FLA, and the minimum load setting is 8% for light-load applications. Intrinsic device protection monitors the thyristors for over-temperature and short-circuit conditions. An external reset input and a display for fault signals are standard. Operating temperature during operation is 60 °C max; storage range is -25 to +80 °C.