The 3RB1257-0KB30: The 125-500 A range covers large motor loads — think 75 kW to 250 kW induction motors at 400 V, depending on service factor and duty cycle. Class 5-30 F means the trip curve is adjustable from fast (class 5, for short overload protection on small motors) to slow (class 30, for high-inertia loads like crushers or centrifuges). The integrated ground fault detection adds a layer of protection that a standard bimetallic overload relay does not provide, which is useful on ungrounded or resistance-grounded systems where a single phase-to-ground fault can go undetected until a second fault occurs.
Deployment Context
The S10/S12 frame size and busbar connection mean this relay mounts directly to a busbar system in a motor control center (MCC) or a large panel — not a standalone DIN-rail mount. The screw-terminal auxiliary circuit and DC 24 V control voltage integrate with standard PLC or relay logic. The manual-automatic-remote reset option lets you configure it for attended or unattended operation.