The Siemens 3RB2133-4QX1 is a SIRIUS solid-state overload relay for three-phase motor protection. It uses straight-through current transformers on the main circuit, eliminating the need to pass cables through a donut — the motor leads terminate directly to the relay's spring-loaded terminals. The trip class is field-adjustable among CLASS 5E, 10E, 20E, and 30E, which means one part number covers fast-acting (5E for short thermal time constants like submersible pumps) through slow (30E for high-inertia loads like centrifuges) without stocking four variants.
The auxiliary contact circuit is rated for 2 A at 24 V, 4 A at 120 V, and 3 A at 230 V — these are the switching capacities for the NC contact (one NC contact is present; zero CO contacts). At 60 VDC the rating drops to 0.55 A, and at 125 VDC it is 0.3 A, so if you are switching a DC control loop at 125 V the contact is limited to 0.3 A. The surge voltage resistance is 6 kV, and EMC burst immunity per IEC 61000-4-4 is 2 kV on power ports and 1 kV on signal ports, severity level 3 — this relay can live in a panel with contactors and drives without external suppression on the auxiliary circuit, though the free-wheel diode rule still applies if you switch an inductive DC load. Relative humidity during operation can be 100 % — no derating for condensation environments. Shock resistance is 15 g for 11 ms, which covers the typical vibration profile of a conveyor transfer station or a compressor skid.
The dimensions are 109 mm depth, 55 mm width, 92 mm height. Clearances: 0 mm upwards, forwards, backwards, and downwards; 6 mm to the side. That zero-clearance spec means the relay can be stacked directly against adjacent devices without derating for airflow, which simplifies panel layout on a tight gland plate. The auxiliary and control circuit uses spring-loaded terminals accepting 2x (0.25... 1.5 mm²) solid or finely stranded with core-end processing, or 2x (24... 16) AWG. No screwdriver torque spec to worry about — spring terminals are vibration-resistant and faster to wire on a production panel build.
ATEX certification is PTB 06 ATEX 3001 Ex II (2) GD, which qualifies it for installation in Zone 2 gas and Zone 22 dust atmospheres when used with appropriately rated enclosures. RoHS substance prohibition date is 07/01/2006, meaning it complies with the original RoHS directive. This documentation package supports the audit trail for a pharmaceutical GMP line — the ATEX cert, the surge/EMC test levels, and the material prohibition date are all on the nameplate and the declaration of conformity.