The Siemens 3RB2133-4QD0 is a SIRIUS solid-state overload relay — three-pole, designed to bolt directly onto a contactor (contactor mounting,) and protect motor circuits from sustained overcurrent without the mechanical fatigue of a bimetal strip. The trip class is adjustable across 5E, 10E, 20E, and 30E, so you dial in the protection curve that matches your motor's start-up profile: fast for short-stall pumps, slower for high-inertia loads like centrifuges or conveyors. Main power terminals are screw-type, rated for 1 x 18–2 AWG or 2 x 4 AWG max, and accept stranded up to 35 mm² — solid enough for a 50–60 A motor circuit. Auxiliary and control connections use spring-loaded terminals, which is the faster termination method for a panel builder wiring signal loops.
Environment and Compliance
This overload relay carries PTB 06 ATEX 3001 Ex II (2) GD certification, meaning it's approved for mounting in the non-hazardous area of a gas/dust zone — the associated apparatus that can sit outside the Ex zone while protecting motors inside it. It shrugs off 15g / 11 ms shock and 100 % relative humidity during operation — no special derating needed for a washdown environment as long as the enclosure is rated. Surge voltage resistance is 6 kV, and burst immunity meets IEC 61000-4-4 severity 3: 2 kV on power ports, 1 kV on signal ports. That's the level you want if the panel shares a cabinet with contactors or VFDs. Lifecycle status is current — this is a catalog-active part, not a phase-out risk.
Fastening method is contactor mounting — it clips directly onto the matching SIRIUS contactor, no DIN rail required. Mounting position is any orientation. The relay body is 55 mm wide, 92 mm tall, 109 mm deep. That zero-clearance top/bottom means it stacks tight in a multi-motor lineup — no air gap needed between relay and contactor above or below. Solid conductors: 2x (0.25... 1.5 mm²) for the aux circuit; finely stranded with ferrule the same. Stranded main conductors: 2x max 25 mm² or single 1–35 mm².
The built-in auxiliary contact set (spring-loaded terminals, 2x 24–16 AWG,) is rated for switching at several common control voltages: 2 A at 24 V, 0.55 A at 60 V, 0.3 A at 110 V, 4 A at 120 V, 0.3 A at 125 V, 0.11 A at 220 V, and 3 A at 230 V.