Motor protection relay for contactor mounting — 17-22 A, Class 10, size S0
The Siemens 3RU6126-4CB0 is a SIRIUS thermal overload relay sized for motor protection in the 17-22 A range, with a Class 10 trip characteristic that clears overloads within 10 seconds at 7.2× Ie — fast enough to protect standard induction motors during stall or jam conditions without nuisance tripping on normal starting curves. Rated for a main circuit voltage of 690 V and a frequency of 50-60 Hz, this three-pole relay mounts directly onto a size S0 contactor (the company-specific S0 frame), saving panel space and eliminating interconnecting wiring between the contactor and overload. Both the main and auxiliary circuits use screw-type terminals; the main terminals accept 2x (0.5-1.5 mm²) solid/stranded or 2x (0.75-2.5 mm²), with a tightening torque of 2-2.5 N·m, while the auxiliary terminals handle 2x (0.5-1.5 mm²) or 2x (0.75-2.5 mm²) as well. The relay's adjustable current response value spans 17-22 A, set via a front dial, and it supports both manual and automatic reset modes — a detail that matters when the motor starter is in a remote or unattended location where automatic restart after a fault is acceptable.
Panel integration and environmental limits
With dimensions of 85 mm depth, 45 mm width, and 85 mm height, the 3RU6126-4CB0 fits the standard S0 contactor footprint and can be mounted in any position. A 6 mm side clearance to grounded parts is required for safe heat dissipation. Relative humidity during operation can reach 90 %, and the relay withstands 8g / 11 ms shock per IEC 60068-2-27 — suitable for installation on vibrating machinery or in mobile equipment. Per-pole dissipation is 2.7 W. These figures drive the thermal budget in a densely packed panel — allow the side clearance and avoid enclosing the relay in a sealed compartment without ventilation. The relay is rated for installation altitudes up to 2 000 m above sea level without derating. Surge voltage resistance is 6 kV, and insulation voltage at pollution degree 3 is 690 V AC.
Lifecycle and compliance — active production, standard documentation
Substance prohibitance compliance date is 05/01/2012, aligning with RoHS and REACH requirements. The relay carries the SIRIUS brand and is designed for motor protection in industrial control panels, typically paired with a size S0 contactor such as the 3RT102 or 3RT103 series. For procurement documentation, the manufacturer provides a CE declaration of conformity, UL/CSA file numbers, and an IEC 60947-4-1 compliance statement. These are available on request at quote time.