Siemens 3RT20161KB41 S00 Coupling Relay
The 3RT20161KB41 is Siemens' size S00 frame coupling relay, designed for DIN-rail or chassis installation in motor control centers, MCC buckets, and control cabinets where a 24 VDC control circuit must switch main-power loads.
The 3RT201 prefix identifies this as an S00 Sirius contactor relay; the sixth-character position encodes the auxiliary contact configuration, with "K" denoting one auxiliary NO contact.
Contact and Coil Specifications
| Parameter | Value |
|---|---|
| Contact Form | 3PST-NO (3 Form A) — main power poles |
| Contact Rating | 9 A (AC-3 duty) |
| Coil Voltage | 24 VDC |
| Coil Power | 2.8 W |
| Coil Current | 116.7 mA |
| Coil Resistance | 205.7 Ω |
| Must Operate Voltage | 16.8 VDC |
| Mounting Type | Chassis Mount, DIN Rail |
| Encapsulation | Bulk |
Coil pickup and drop-out
The must-operate threshold of 16.8 VDC provides a 30 % voltage margin above the nominal 24 VDC coil rating, which accommodates voltage drop in long control wiring runs common in distributed MCC configurations.
Main pole arrangement
The three Form A contacts serve as the main switching poles for AC-3 (motor switching) duty, rated at 9 A — appropriate for motors up to approximately 4 kW at 400 VAC.
Product Family Variants
The 3RT20161xB41 series shares the S00 frame, 24 VDC coil, and 9 A contact rating; variants diverge on auxiliary contact type and package style.
| MPN | Auxiliary | Coil Power | Encapsulation | Must Operate |
|---|---|---|---|---|
| 3RT20161KB41 | 1 NO | 2.8 W | Bulk | 16.8 VDC |
| 3RT20161KB42 | 1 NC | 2.8 W | Box | 16.8 VDC |
| 3RT20161JB41 | 1 NO | 2.8 W | Bulk | 16.8 VDC |
| 3RT20161QB41 | 1 NO | 2.8 W | Box | 16.8 VDC |
| 3RT20161WB41 | 1 NO | 1.6 W | Box | 20.4 VDC |
| 3RT20161SB41 | 1 NO | 1.6 W | Box | 20.4 VDC |
Higher-coil-resistance variants (WB41, SB41) draw less holding current but raise the must-operate threshold to 20.4 VDC, reducing margin in extended wiring runs.
The KB42 variant substitutes a normally-closed auxiliary contact, suitable for feedback or interlock circuits rather than command signaling.