Siemens 3RH5921-1FA22

1.  Basic Product Information

3RH5921-1FA22 is a front-mounted auxiliary contact module of the Siemens SIRIUS series, with a standard configuration of 2NO+2NC (2 Normally Open + 2 Normally Closed). It adopts screw terminal connection and is compatible with 3RT5/3RT6 series contactors and 3RH series contactor relays. It is a key component for signal expansion and logic interlocking in industrial control circuits.

2.  Core Technical Parameters

3.  Working Principle

This auxiliary contact module acts synchronously with the main contacts of the contactor/relay through a mechanical linkage mechanism:

1.  Initial State (De-energized): The normally closed contacts (21-22, 41-42) remain closed, and the normally open contacts (13-14, 33-34) remain open.
2.  Operating State (Main Contact Closure): After the contactor coil is energized, the mechanical transmission mechanism drives the auxiliary contacts to switch synchronously—the normally closed contacts open and the normally open contacts close, realizing the logic switching of the control circuit.
3.  Reset State (Power-off Release): When the coil is de-energized, the reset spring pushes the contacts back to their initial position, ensuring the synchronous reset of the circuit state.
4.  Structural Features and Advantages
5.  Quick Installation Design: Adopts snap-on front mounting, which can be assembled without additional tools, improving the efficiency of cabinet wiring.
6.  Modular Expansion: A single module provides 4 channels of contacts, which can be combined with other auxiliary modules to meet complex control requirements.
7.  Clear Identification: Terminal numbers follow Siemens standards (1-2 for normally closed, 3-4 for normally open), facilitating circuit design and fault troubleshooting.
8.  High Reliability: Copper alloy contact material with excellent electrical conductivity and wear resistance. The short bounce time of contact switching reduces arc damage to the contacts.
9.  Strong Compatibility: Compatible with all Siemens 3RT5/3RT6 series contactors and 3RH series contactor relays, with high versatility.
10.  Typical Application Scenarios
11.  Motor Control Circuit Expansion

Scenarios: Forward and reverse control of production line motors, star-delta starting conversion, speed regulation of multi-speed motors.

Logic: Normally open contacts are used to control the contactor coil, and normally closed contacts are used for interlock protection to prevent power supply short circuit.

2.  Status Indication and Alarm

Scenarios: Equipment running indicator light, fault alarm light, power supply status display.

Logic: Normally open contacts are connected in series with the indicator light circuit. The light turns on when the contactor pulls in, intuitively reflecting the equipment running status.

3.  PLC Signal Acquisition

Scenarios: Equipment status monitoring and action feedback of automation systems.

Logic: Auxiliary contacts are connected to the PLC digital input module to convert the contactor action status into electrical signals, realizing closed-loop system control.

4.  Safety Circuit Interlocking

Scenarios: Emergency stop circuit, safety door interlock, overload protection interlock.

Logic: Normally closed contacts are connected in series with the safety circuit. The circuit is automatically cut off when the contactor fails, ensuring the safety of personnel and equipment.

6.  Selection and Replacement Suggestions
7.  Compatible Contactor Specifications: S00-S3 (corresponding to 3RT50/51/52 series), not applicable to large-size contactors of S4 and above.
8.  Terminal Type Selection: If spring terminal connection is required, 3RH5921-2FA22 can be used as an alternative.
9.  Contact Quantity Expansion: A single contactor can be equipped with up to 2 front auxiliary modules, providing a maximum of 8 channels of contacts (4NO+4NC).
10.  Alternative Model: If side-mounted auxiliary contacts are required, the 3RH69 series (e.g., 3RH6911-1HA22) can be selected.