Solid-state motor protection for S0 contactors
The 3RB3123-4QB0: It mounts directly onto the contactor (fastening method: contactor mounting), so the assembly stays within the same DIN-rail footprint as the contactor itself — no extra panel space for a separate overload block.
Trip class adjustability and motor current window
Trip class is field-adjustable across CLASS 5E, 10E, 20E, and 30E — the same relay can be set for fast tripping on a pump (5E) or slower tripping on a high-inertia fan (30E) without swapping hardware. The motor current must fall between the lower current setting value and the upper setting value x 3.5 — this defines the usable motor FLA window the relay can protect.
Screw terminals require a Pozidriv PZ2 tip with a 5 to 6 mm shaft diameter — standard electrician's screwdriver, no special tooling.
Environmental tolerance and mounting flexibility
Shock resistance is 15g / 11 ms (signaling contact in tripped position: 9g / 11 ms), and vibration resistance covers 1-6 Hz at 15 mm amplitude and 6-500 Hz at 20 m/s² over 10 cycles — this relay holds calibration on a conveyor line or a compressor skid.
This is a solid-state overload relay, not a bimetallic thermal type — it uses current measurement and an electronic trip circuit, so it provides temperature-compensated protection and adjustable trip class without heating elements.