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Siemens 3RH1921-1CA01 auxiliary switch block
The Siemens SIRIUS 3RH1921 series auxiliary switch blocks snap onto the front of 3RT1 contactors and give the PLC a feedback signal of the contactor’s switching state.
Why does a contactor need auxiliary contacts? The main contacts of a contactor switch the high-current circuit of a motor or load, but the PLC or control system often needs to know whether the contactor has actually operated. Auxiliary contacts are low-current contacts that provide this feedback: when the coil is energized and the main contacts close, the auxiliary contacts change state at the same time and send the signal back to the PLC — essential for fault diagnosis, interlocking and sequence control.
Specifications
| Item | Details |
|---|---|
| Model | 3RH1921-1CA01 |
| Brand | Siemens SIRIUS |
| Contacts | 1NC |
| Mounting | Front snap-on |
| Terminals | Screw terminals |
| Rated operational voltage | 690 VAC / 600 VDC |
| Rated operational current | AC-15: 6 A at 230 V / AC-12: 10 A |
| Mechanical life | 10 million operations |
| Electrical life | 200,000 operations |
| Protection | IP20 |
| For contactors | Siemens 3RT1 series (sizes S0–S12) |
| Approvals | CE / UL / CSA / CCC / EAC |
3RH1921 series contact versions
| Model | Contacts | Poles | Notes |
|---|---|---|---|
| 3RH1921-1CA01 | 1NC | 1 | Normally closed (this product) |
| 3RH1921-1CA10 | 1NO | 1 | Normally open |
| 3RH1921-1DA11 | 1NO + 1NC | 2 | One NO, one NC |
| 3RH1921-1FA22 | 2NO + 2NC | 4 | Four-pole block |
| 3RH1921-1EA11 | 1NO + 1NC | 2 | Spring-type terminals |
Combining blocks: up to four single-pole auxiliary switches (or one four-pole block) can be fitted to the front of each 3RT1 contactor. NC contacts open before NO contacts close, keeping interlocking reliable.
Selection note: the 3RH1921 is for 3RT1 contactors. For the newer 3RT2 series, choose 3RH2921 auxiliary switches (slightly different shape and interface). Please confirm your contactor generation and model before ordering.
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