How to Install and Reset Siemens SIRIUS Thermal Overload Relays

You can install and reset a Siemens SIRIUS thermal overload relay by mounting it on a compatible contactor, wiring motor leads through its terminals, adjusting settings to the motor’s full load amps, and using the reset button or selector switch after a trip.

Ensuring Reliable Motor Protection

Thermal overload relays safeguard motors from damaging conditions like prolonged overcurrent, phase imbalance, and overheating. The Siemens SIRIUS thermal overload relay series is engineered to provide dependable motor protection in demanding industrial applications..

This article provides a step-by-step installation guide along with clear reset instructions, supported by practical troubleshooting advice. We will also reference the Siemens overload relay wiring diagram and highlight the importance of sourcing genuine devices for reliable performance.

Understanding Siemens SIRIUS Thermal Overload Relays (3RU Series)

The Siemens SIRIUS 3RU thermal overload relays are part of the SIRIUS control portfolio and are designed to protect motors up to 37 kW within a current range of 0.11–100 A. They operate using bimetallic trip technology, where heat generated by excess current bends a strip, triggering the relay to open and interrupt the motor circuit.

Key points:

• Model Example: Siemens 3RU Thermal Overload Relays
• Protection Scope: Overload, phase imbalance, and phase loss.
• Reset Options: Manual and automatic reset.
• Contacts: Each relay provides 1 NO + 1 NC auxiliary contact for control circuit integration.

When paired with a Siemens 3RT505 AC/DC Contactor, these relays form a robust motor starter combination suitable for pumps, compressors, and conveyor systems.

Step-by-Step Installation Guide

Proper installation is the foundation of reliable motor protection. Follow this structured process:

1. Safety First

Always begin by disconnecting all power supplies. Confirm with a test meter that circuits are de-energized before handling wiring.

2. Mounting the Relay

The Siemens SIRIUS 3RU relays are designed for direct mounting beneath a SIRIUS contactor such as the 3RT505 AC/DC Contactor. The relay and contactor mechanically latch together, creating a compact motor starter. For standalone use, a terminal bracket can be employed.

3. Power Wiring

• Connect the motor leads to the relay’s main terminals (T1, T2, T3).
• Ensure all three phases pass through the relay’s bimetal elements, which allows it to detect overload and phase loss conditions.

4. Control Circuit Wiring

• Wire the relay’s NC contact (95–96) in series with the contactor coil.
• If the relay trips, this NC contact opens, de-energizing the coil and disconnecting the motor.
• The NO contact (97–98) can be wired for indication lamps or alarms.

After the steps above, adjust the dial on the relay front to match the motor’s Full Load Amps (FLA) from its nameplate. For example, a 7–10 A motor would typically use a 3RU21 16-1JB0 relay set accordingly. By carefully following this Siemens overload relay wiring diagram process, you ensure both safety and correct operation.

How to Reset a Siemens SIRIUS Overload Relay

Resetting is simple once you understand the relay’s functions:

1. Identify the Trip

A trip indicator on the relay shows whether an overload condition has occurred.

2. Allow Cooling Time

Thermal relays must cool before being reset. This usually takes about 10 minutes, though it depends on ambient temperature and the severity of the overload.

3. Manual Reset

Press the blue reset button on the relay front. This restores the NC contact and allows the contactor coil to energize again.

4. Automatic Reset

Many Siemens SIRIUS thermal overload relays include a selector switch for manual or automatic reset. In automatic mode, the relay resets itself after cooling. This is convenient for unattended equipment, but should be applied carefully to avoid repeated cycling in persistent fault conditions.

5. Remote Reset

For advanced systems, Siemens offers mechanical or electrical remote reset modules that integrate into automation setups, which are useful for inaccessible panels.

For hands-on visuals, users often refer to resources like how to reset Siemens solid state relay overload assembly YouTube, which demonstrates real relay operation.

Troubleshooting Common Installation and Reset Issues

Even with correct installation, operators may encounter issues:

Relay Trips Immediately After Reset

Likely causes: Incorrect FLA setting, motor fault, or wiring error. Confirm motor current rating and recheck the Siemens overload relay wiring diagram.

Relay Won’t Reset

Ensure adequate cooling time. If persistent, the relay may be defective or experiencing continuous overload.

Contactor Not Pulling In After Reset

Verify the control wiring between the relay contacts and the contactor coil. Also, check the auxiliary NO/NC contacts for proper function.

Frequent Nuisance Trips

May indicate an undersized relay. Confirm that the selected relay matches motor FLA, or consider a higher trip class relay.

Sourcing Genuine Siemens Relays and Expert Support from Simply Buy

When working with protective devices, reliability is paramount. At Simply Buy, we supply only 100% genuine Siemens SIRIUS thermal overload relays and contactors. By sourcing directly from manufacturers, we guarantee compliance with Siemens’ specifications.

• Explore the Siemens 3RU Thermal Overload Relays for motor protection up to 37 kW.
• Pair them with the Siemens 3RT505 AC/DC Contactor for high-performance motor starter combinations.

We also provide:

• Official Siemens manuals and wiring diagrams for clear guidance.
• Technical support to help customers resolve installation or reset issues quickly.
• Competitive global delivery for all Siemens products.

With the right relay and expert support, your motors are protected, downtime is minimized, and your system operates with confidence.

Conclusion

Knowing how to install Siemens SIRIUS thermal overload relay devices and reset them after a trip is essential for reliable motor operation. By mounting properly, wiring according to diagrams, setting FLA correctly, and using manual or automatic reset functions, you can ensure dependable product performance. When paired with genuine contactors like the 3RT505, Siemens overload relays deliver the protection today’s industrial systems require.