Siemens 3RT20181BB42 Contactor — S00 Frame, 16 A, 24 VDC Coil
MPN Structure and Series Overview
The Siemens 3RT20181BB42 belongs to the 3RT2018 family of SIRIUS S00-size contactors. The MPN suffix encodes two key dimensions: the character pair occupying positions 9–10 specifies the coil voltage class (BB = 24 VDC), while positions 11–12 define the auxiliary contact arrangement (42 = one NC auxiliary contact, front-mounted screw terminals). The main power poles are configured as three Form A (3PST-NO), rated at 16 A, with a 4 W DC coil.
Contact Arrangement Comparison
The primary part carries one NC auxiliary contact. Catalog peers sharing the same base number differ in auxiliary contact layout; three in-catalog variants illustrate the range.
| Parameter | 3RT20181BB42 | 3RT20181BB41 | 3RT20181BB443MA0 |
|---|---|---|---|
| Auxiliary Contacts | 1 NC | 1 NO | 2 NO / 2 NC |
| Coil Voltage | 24 VDC | 24 VDC | 24 VDC |
| Coil Power | 4 W | 4 W | 4 W |
| Main Contact Rating | 16 A | 16 A | 16 A |
| Mounting | Chassis / DIN Rail | Chassis / DIN Rail | Chassis / DIN Rail |
| Encapsulation | Bulk | Bulk | Bulk |
Auxiliary Contact Needs
The 1NC variant (3RT20181BB42) suits circuits requiring a normally-closed monitoring or interlock signal that opens on coil energization. The 1NO variant (3RT20181BB41) provides the inverse logic. Where two independent auxiliary contacts are needed — for example, separate run and overload acknowledgment signals — the 2NO/2NC arrangement (3RT20181BB443MA0) eliminates a separate relay block.
Voltage Class Alternatives
Other catalog entries in the same 3RT2018 base series apply different coil voltages while preserving the 1NC auxiliary pattern.
| Parameter | 3RT20181BB42 | 3RT20181BA42 | 3RT20181BW42 | 3RT20181BM42 |
|---|---|---|---|---|
| Coil Voltage | 24 VDC | 12 VDC | 48 VDC | 220 VDC |
| Must-Operate Voltage | 19.2 VDC | 9.6 VDC | 38.4 VDC | 176 VDC |
| Coil Power | 4 W | 4 W | 4 W | 4 W |
| Contact Rating | 16 A | 16 A | 16 A | 16 A |
The must-operate voltage scales proportionally with coil voltage class (80 % of nominal), maintaining the same 4 W coil consumption across the BB, BA, BW, and BM voltage selections.
General Specifications
| Parameter | Value |
|---|---|
| Base Product Number | 3RT2018 |
| Contact Form | 3PST-NO (3 Form A) |
| Contact Rating | 16 A |
| Coil Voltage | 24 VDC |
| Coil Power | 4 W |
| Coil Current | 166.7 mA |
| Coil Resistance | 144 Ω |
| Must-Operate Voltage | 19.2 VDC |
| Mounting Type | Chassis Mount, DIN Rail |
| Features | Auxiliary Contacts |
| Encapsulation | Bulk |
| Manufacturer | Siemens |
Coil resistance of 144 Ω and a must-operate voltage of 19.2 VDC are consistent with the 24 VDC nominal coil rating at approximately 166.7 mA pull-in current.
Similar Catalog Parts
The 3RT2018 family extends beyond the auxiliary-contact variants listed above. Catalog entries such as 3RT20181BB420CC0, 3RT20181BB410UA0, and 3RT20181BB410CC0 share the same 24 VDC coil and 16 A main contact rating but differ in packaging (Box vs. Bulk) and, for some entries, operating temperature range (25°C–60°C). Voltage-class peers — 3RT20181BA42 (12 VDC), 3RT20181BW42 (48 VDC), and 3RT20181BM42 (220 VDC) — carry the same 1NC auxiliary contact suffix while varying coil voltage. All listed parts require the reader's own technical qualification before use as alternatives.