Siemens SIRIUS 3RU2 Thermal Overload Relays

Siemens SIRIUS 3RU2 Thermal Overload Relays Suppliers, Exporters in India

Siemens SIRIUS 3RU2 Thermal Overload Relays protect three-phase motors against excessive current, prolonged overload and phase failure. They are normally fitted below a Siemens SIRIUS contactor in motor starters, control panels and motor control centres.

The relay monitors the current drawn by the motor through three bimetal elements. When the motor continues to draw more current than the selected setting, the elements heat up and operate the relay contacts. The normally closed contact disconnects the contactor coil, while the normally open contact can send a trip indication to a lamp, alarm or PLC.

The 3RU2 range covers motor currents from approximately 0.11 A to 100 A, with different models for S00, S0, S2 and S3 contactor sizes. Siemens supplies versions for direct mounting on a contactor as well as separate mounting inside the panel.

These relays are mainly used for motors with normal starting conditions. The current setting can be adjusted to match the motor’s rated current shown on the nameplate. Manual and automatic reset options allow the panel builder to select how the motor should return to service after an overload trip.

ARP IMPEX supplies and exports Siemens SIRIUS 3RU2 Thermal Overload Relays for motor starters, control panels, industrial machinery and replacement requirements. Share the complete Siemens part number or motor current range for price and availability.

Technical Specifications

• Brand: Siemens
• Product range: SIRIUS
• Series: 3RU2
• Product type: Thermal overload relay
• Protection function: Motor overload and phase-failure protection
• Operating principle: Thermal bimetal release
• Current range: Approximately 0.11 A to 100 A across the series
• Available sizes: S00, S0, S2 and S3
• Trip class: Class 10
• Motor type: Three-phase AC motors
• Number of poles: Three
• Current setting: Adjustable within the range of the selected relay
• Reset options: Manual or automatic reset
• Auxiliary contacts: One normally closed contact and one normally open contact
• Mounting options: Direct contactor mounting or separate panel mounting
• Main terminal options: Screw or spring-loaded terminals, depending on the model
• Auxiliary terminal options: Screw or spring-loaded terminals, depending on the version
• Test function: Available through the front TEST control
• Stop function: Front STOP control
• Temperature compensation: From -40°C to +60°C
• Operating temperature: Up to +70°C on standard models, subject to derating and installation conditions
• Front protection: IP20
• Compatible equipment: Siemens SIRIUS contactors and motor starters

Current ranges, terminal arrangements and mounting options vary by article number. The exact relay should be selected according to the motor rated current and the compatible contactor frame size.

Features

• Adjustable current setting allows the relay to match the motor nameplate current.
• Thermal bimetal operation does not require a separate control supply.
• Phase-failure sensitivity helps protect motors running under an unbalanced supply.
• Manual reset prevents an unexpected restart after the relay trips.
• Automatic reset can be selected where the control circuit safely allows it.
• The TEST control helps check the trip circuit and auxiliary-contact wiring.
• The STOP control can open the contactor control circuit during testing or maintenance.
• One normally closed contact switches off the contactor after a trip.
• One normally open contact can operate an alarm, an indication lamp or a PLC input.
• Temperature compensation reduces the effect of normal changes in panel temperature.
• Direct mounting provides a compact motor-starter assembly.
• Separate mounting versions suit panels where the relay cannot be installed directly below the contactor.
• Different current ranges cover fractional motors as well as motors drawing up to 100 A.
• The range matches Siemens SIRIUS contactor sizes from S00 to S3.
• Front current adjustment and reset controls remain accessible after installation.

The relay’s TEST function simulates a trip by opening the NC contact and closing the NO contact. After a real overload trip, the bimetal elements must cool before the relay can be reset.

Applications

• Siemens SIRIUS 3RU2 Thermal Overload Relays are commonly used in:
• Direct-on-line motor starters
• Reversing motor starters
• Star-delta starter panels
• Motor control centres
• Pump control panels
• Compressor control panels
• Industrial fans and blowers
• Conveyor systems
• Packaging machines
• Machine tools
• Mixers and agitators
• HVAC equipment
• Water-treatment plants
• Material-handling systems
• Production and assembly machinery
• Process plant equipment
• Electrical control panels
• Industrial maintenance and motor-starter replacement

Selecting the Correct Siemens 3RU2 Relay

The adjustable current range of the overload relay must cover the rated current shown on the motor nameplate. For example, a motor with a rated current of 18 A requires a relay range that includes 18 A. Selecting the relay only by motor power can lead to the wrong product because the motor current changes with voltage, efficiency and operating conditions.

The relay must also match the Siemens contactor size and mounting arrangement. Buyers replacing an existing unit should share the complete 3RU2 part number printed on the relay. When the part number is unavailable, provide the motor power, rated current, operating voltage, contactor part number and required mounting type.

A thermal overload relay does not provide short-circuit protection. The motor circuit still requires a suitable fuse, motor protection circuit breaker or short-circuit protective device selected according to the panel design and coordination requirements.

Siemens 3RU2 Thermal Overload Relay Supplier and Exporter

ARP IMPEX supplies Siemens SIRIUS 3RU2 Thermal Overload Relays for panel builders, machine manufacturers, EPC contractors, factories and industrial maintenance companies.

The range includes low-current S00 relays, S0 and S2 motor-protection models and S3 relays with adjustable current ranges up to 100 A. Direct-mounting and separate-mounting versions are available against the required Siemens article number.