Siemens 3RT20231BB40 Size S0 Contactor

System Integration Context

The 3RT20231BB40 is a Size S0 electromechanical contactor from Siemens' 3RT2 family, commonly mounted in motor-control centres (MCCs), busbar compartments, and distributed IO cabinets where 24 VDC coil drive is available from the control architecture. Its chassis/DIN-rail mounting enables panel builders to install in a single module without custom bracketry, while the 1NO+1NC auxiliary configuration supports both contact confirmation and interlock chaining in low-power loads. The 9 A contact rating places it in the lower end of the Size S0 range, making it suitable for driving small AC-3 loads or as an auxiliary relay in higher-power starters.

Contact and Coil Options

Contact Arrangement and Current Handling

The primary pole configuration for the 3RT20231BB40 is a three-pole normally-open (3PST-NO / 3 Form A) arrangement, suitable for switching three-phase loads such as motors, heaters, or capacitors in AC-3 duty. Contact rating is specified at 9 A, which aligns with the Size S0 frame in Siemens' 3RT2 series. The auxiliary contact complement is 1NO/1NC, useful for feedback signalling and control-circuit interlock in simpler starter assemblies; this does not provide redundancy for the power poles but is adequate for sequencing and status indication.

Coil Voltage Family and Operate Points

The coil supplied with the 3RT20231BB40 is rated 24 VDC, drawing 5.9 W during energisation. The must-operate voltage is specified as 19.2 VDC, giving a comfortable margin above nominal 24 VDC supply rails and accommodating modest voltage drop in long control wiring runs. The in-catalog alternates span the same Size S0 / 9 A / 5.9 W frame across several DC coil voltages:

All alternates share the same base product number (3RT2023), the same coil power consumption (5.9 W), the same contact rating (9 A), and the same mounting type (chassis or DIN rail). The differences are in coil voltage and the auxiliary contact count (1NO/1NC versus 2NO/2NC). Operate time is listed for all Box-packaged alternates at 170 ms; this parameter is absent for the bulk-seed variant but likely falls in the same range.

Operating Temperature

Operating temperature range is 25°C to 60°C for the seed and most alternates, with minor notation variations (space before the unit symbol). This range is typical for enclosed panel environments and covers most indoor industrial applications; thermal derating for higher ambient conditions or enclosed cubicle mounting would require review against the specific installation envelope.

Similar Catalog Parts

The 3RT20231BB40 sits within a tightly grouped family of Size S0 / 9 A / 5.9 W DC-coil contactors. The table below provides a side-by-side comparison across shared spec keys. These parts are catalog peers requiring user qualification and are not OEM-endorsed direct substitutes.

Why they are similar

All share the same base product family (3RT2023) and identical electromechanical platform: 9 A three-pole, 5.9 W DC coil, chassis/DIN-rail mount. The alternates differ only in coil voltage (supporting different control architectures) and, for the BB44/BB443MA0 variants, in auxiliary contact count (2NO/2NC instead of 1NO/1NC). The primary distinction is the must-operate voltage scaling proportionally with the coil rating — e.g., the 60 VDC variant requires 48 VDC minimum, which precludes drop-in substitution on a 24 VDC supply.