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Siemens 3RH1921-1FA31 Auxiliary Switch Block 3NO+1NC

The 3RH1921-1FA31 is a high-performance soft starter from the Siemens SIRIUS 3R series. It is used to smoothly start and stop three-phase AC induction motors by controlling the voltage applied to the motor, effectively reducing inrush current and mechanical stress during startup, thereby extending the service life of the motor and connected equipment. This model features an integrated bypass contactor. Once the motor reaches full speed, the thyristors within the soft starter are bypassed, and the motor is directly supplied via mechanical contacts, reducing losses and heat generation in the soft starter itself.

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Product Description

Detailed Description:

  • Soft Starting & Stopping: Achieves gentle motor acceleration (soft start) by gradually increasing voltage and can also achieve gentle deceleration and stopping (soft stop) by gradually decreasing voltage. Ideal for applications like pumps, fans, and conveyor belts where reducing water hammer, vibration, or material slippage is important.

  • Integrated Bypass Function: The suffix “1FA31” in the model number indicates that this soft starter integrates a bypass contactor. After startup is complete, this contactor engages, switching the motor main circuit to bypass mode. This ensures the thyristors only operate during start and stop phases, reducing energy consumption and temperature rise.

  • Protection Features: Provides comprehensive motor protection, including overload protection, phase loss protection, motor stall protection, and thyristor overtemperature protection.

  • Flexible Control: Supports multiple control modes, including voltage ramp start and current limit start. Offers local control terminals (e.g., Start, Stop, Reset) and programmable relay outputs for status indication or interlocking with other devices.

  • Compact Design: Features a modular, compact design for mounting on standard DIN rails, saving control cabinet space. The front panel includes LED indicators showing power, run, fault, and other statuses.

  • Application Areas: Widely used for motor control of loads such as fans, pumps, compressors, conveyors, and mixers. Particularly suitable for applications with frequent starts/stops or where strict limits on grid inrush currents are required.

Key Specifications:

Parameter Details
Model 3RH1921-1FA31
Series SIRIUS 3R
Rated Operational Current 40 A (at 40°C ambient temperature)
Rated Control Supply Voltage Typically 24 V DC or 110-240 V AC (depends on ordering code)
Motor Rated Power Suitable for approx. 18.5 kW / 25 HP three-phase motor (at 400V)
Start Control Voltage Ramp Start, optionally Current Limit Start
Integrated Feature Built-in Bypass Contactor
Protection Functions Overload, Phase Loss, Stall, Thyristor Overtemperature
Control Inputs Digital inputs for Start, Stop, Reset, etc.
Relay Outputs Programmable relay contacts for status or fault indication
Protection Rating IP20 (for installation inside control cabinet)
Mounting DIN Rail Mounting
Commissioning Basic settings via potentiometers or DIP switches on the unit

What Happens After You Order?

1
Step 1

Order Confirmed

Receive email confirmation once your order or quote is received. We review your request and prepare your parts for the next step.

2
Step 2

Personal Representative

A dedicated rep contacts you to verify specs, confirm shipping details, and answer any questions before dispatch.

3
Step 3

Tested & Shipped

Parts go through rigorous final testing. Once verified, your order is carefully packed and shipped with full tracking info.

FAQ

What is your main line of business?

We specialize in the supply and repair of industrial automation components and CNC spare parts. Our inventory covers 20+ world-class brands including Fanuc, Siemens, Mitsubishi, Lenze, IFM, and SICK, featuring 100,000+ SKUs in stock. Whether you need servo drives, PLC modules, motors, encoders, or sensors, we provide tested, ready-to-ship solutions for both new and refurbished parts.

Where is your company? How do I get there?

Our headquarters is located at Rooms 801–802, Building A1-2, Area A, Guangda We Valley, Zongbu 2nd Road, Songshan Lake Park, Dongguan City, Guangdong Province, China. Our facility is equipped with professional testing labs and a clean, modern warehouse environment.

Do you have test equipment? How long is the delivery time?

Yes — we maintain complete in-house testing equipment, and 100% of parts are fully tested before shipment. Most items are in stock and ready for immediate dispatch. For stocked items, we offer 48-hour express global delivery; standard worldwide shipping typically arrives within 7 days.

What's the warranty on your parts?

New parts: 1 year
Used : 3 months

If a part does not function properly upon receipt, please contact our customer service team immediately and provide a clear video showing the issue. Once verified, you may return it to us within 7 days for an exchange or refund. Returns without prior contact and video evidence may not be accepted.

How about the packing when they are sent out?

All shipments are carefully protected with foam padding to fill every space inside the box, ensuring parts remain secure during transit. We typically use reinforced cardboard boxes; for heavier or high-value items, we provide custom wooden crates for added protection.

What deliveries are available?

We ship globally via UPS, DHL, FedEx, TNT, and EMS, with flexible options to match your urgency and budget.

OUKE Automation is not an authorized distributor unless otherwise specified, representative, or affiliate of the manufacturer of this product. All trademarks and documents are the property of their respective owners and are provided for identification and informational.

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