Solid-state overload relay for motor protection
The Siemens 3RB2133-4UW1 is a SIRIUS solid-state overload relay rated for 3-pole main current circuits with straight-through transformers and screw-type terminals for auxiliary and control wiring. It protects motors by monitoring current and tripping when an overload condition persists beyond the selected trip class. Trip class is field-adjustable among CLASS 5E, 10E, 20E, and 30E, letting you match the relay's response to the motor's starting profile — a 5E setting for short-duration starts like centrifugal pumps, or 30E for high-inertia loads such as conveyors or crushers. The relay carries ATEX certification PTB 06 ATEX 3001 Ex II (2) GD, meaning it is approved for use in potentially explosive atmospheres as an associated apparatus — the (2) indicates it can be installed outside the hazardous zone but must be connected to equipment within it per the installation directive.
Mounts in any position via stand-alone installation — no DIN-rail adapter required, though the 55 mm width and 92 mm height are compatible with standard enclosure layouts. Depth is 109 mm, which is the dimension to check when closing a shallow panel door or fitting alongside busbars. This zero-clearance stacking on four faces allows dense panel packing, but the side gap of 6 mm must be maintained for heat dissipation. Withstands 100 % relative humidity during operation and shock of 15g for 11 ms — suitable for installation on vibrating machinery or in unconditioned enclosures.
Electrical ratings and auxiliary contacts
The auxiliary contact block provides 1 NC contact (no CO contacts). Switching capacity varies with voltage: 2 A at 24 V, 4 A at 120 V, 3 A at 230 V, and lower ratings at 60 V (0.55 A), 110 V (0.3 A), 125 V (0.3 A), and 220 V (0.11 A). These are the maximum currents the NC contact can break at those voltages — use them to confirm the control circuit load. Surge voltage resistance is rated at 6 kV, and immunity to electrical fast transients (burst) per IEC 61000-4-4 is 2 kV on power ports and 1 kV on signal ports, severity level 3. This meets the EMC requirements for industrial environments without external filtering in most installations.
Wiring and conductor specifications
Screw-type terminals accept solid conductors from 0.5 to 4 mm², or two conductors of 0.5 to 2.5 mm² each. For finely stranded wire with ferrule, the range is 0.5 to 2.5 mm², or two conductors of 0.5 to 1.5 mm². AWG equivalents for auxiliary contacts are 2x (20 to 14).
Substance prohibition date per RoHS-like requirements is 07/01/2006, confirming compliance with the original RoHS directive.