Siemens 3RH1921-2FA31 Auxiliary Contact Block

Description

Siemens 3RH1921-2FA31 Auxiliary Contact Block

Product Dimensions：

The Siemens 3RH1921-2FA31 is a high-reliability auxiliary switch block belonging to the SIRIUS family of industrial control products. It is designed to expand the contact capacity of Siemens size S00 to S3 contactors and contactor relays.

Product Detailed Description

The 3RH1921-2FA31 is a front-mounted, modular auxiliary contact block. It provides additional control and signaling contacts for main switching devices. This specific variant utilizes spring-loaded (Cage Clamp) terminals, which offer excellent resistance to vibrations and eliminate the need for periodic retightening.

The contact configuration is 4-pole, arranged as 3 NO (Normally Open) + 1 NC (Normally Closed) contacts.

Technical Parameters

Product Advantages

• Vibration-Proof Connection: The spring-loaded terminal technology ensures a secure, gas-tight wire connection that remains tight even in high-vibration environments, such as near large motors or on marine vessels.
• Tool-Less Installation: Easily snaps onto the front of compatible SIRIUS 3RT contactors or 3RH contactor relays without the need for mounting screws or specialized tools.
• Space Optimization: Front-mounting expands control capabilities without increasing the width of the main contactor, conserving valuable DIN rail space.
• High Reliability: Mechanically linked contacts ensure high switching reliability for interlocks and feedback signals in safety-related circuits.

Important Considerations & Precautions

• Compatibility: This module is designed strictly for the Siemens SIRIUS range (typically sizes S00 through S3). Verify your specific main contactor model series before ordering.
• Electrical Ratings: Do not exceed the rated operational current (I_e) for the specific utilization category. For example, DC-13 (inductive DC loads) has a significantly lower current rating than AC-15 (inductive AC loads).
• Wire Stripping: When using spring terminals, ensure wires are stripped to the correct manufacturer-specified length to prevent insulation from being caught in the clamp or exposed conductive wire outside the housing.
• Single Placement: Generally, only one 4-pole front-mounted auxiliary block can be attached to a single contactor.

Product Applications

The 3RH1921-2FA31 is utilized across automated control panels to manage auxiliary functions:

• Electrical Interlocking: Preventing two conflicting contactors (such as Forward and Reverse in a motor starter) from closing at the same time.
• Status Signaling: Providing feedback to a PLC input module regarding the physical state (Open/Closed) of the main contactor.
• Control Circuit Expansion: Switching pilot lights, audible alarms, or auxiliary cooling fans when the main load is energized.
• Holding Circuits: Used as a latching contact in traditional push-button start/stop motor control circuits.

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