3RU1136-4HB0 Thermal Overload Relay (Industrial-Grade Motor Safeguard)

The 3RU1136-4HB0 represents Siemens' proven approach to three-phase motor protection, combining Class 10 thermal trip technology with field-proven reliability for 40-50 ampere applications. This overload relay integrates seamlessly into SIRIUS motor control assemblies, delivering proportional thermal response that mirrors actual motor heating patterns while preventing costly downtime from phase failures and sustained overload conditions.

Designed for industrial facilities where motor-driven equipment operates continuously under variable load conditions, this relay addresses the critical challenge of distinguishing between acceptable startup inrush and dangerous fault currents. Manufacturing plants, water treatment facilities, and material handling operations rely on this protection device to maintain uptime while safeguarding expensive motor assets from thermal damage.

With adjustable current settings, dual reset modes, and direct snap-on contactor mounting, the 3RU1136-4HB0 reduces installation time by 40% compared to separately mounted protection devices while ensuring IEC 60947-4-1 compliance for global industrial standards.

Core Features & Benefits

✓ Adjustable 40-50A Range: Precision dial adjustment accommodates motors with varying full-load currents without requiring multiple relay models, reducing inventory complexity and enabling quick motor replacements.

✓ Class 10 Trip Characteristic: Temperature-compensated bimetal elements provide 10-second maximum trip time at 7.2× rated current, allowing brief overloads during startup while responding rapidly to locked-rotor conditions.

✓ Dual-Mode Reset Function: Field-selectable manual or automatic reset adapts to operational requirements—manual mode enforces fault investigation protocols, automatic mode suits remote installations requiring self-recovery capability.

✓ Three-Phase Monitoring: Simultaneous tracking of all three phases detects phase loss, voltage imbalance, and asymmetric loading conditions that single-phase protection would miss, preventing single-phasing damage.

✓ Direct Contactor Integration: Snap-on mounting to SIRIUS 3RT contactors eliminates 12 wire terminations and reduces panel footprint by 35%, accelerating assembly and simplifying maintenance access.

✓ Wide Voltage Compatibility: Operates across 24-690V AC systems without derating, supporting diverse motor control applications from small machinery to industrial process equipment.

Application Scenarios

Conveyor & Material Handling Systems: Protects belt conveyor drives, bucket elevators, and screw conveyors in mining, agriculture, and logistics facilities where motors experience frequent starts, variable loads, and dusty environments. The relay's thermal memory prevents nuisance trips during sequential restart cycles while catching bearing failures that manifest as gradual current increases.

Pump & Compressor Stations: Safeguards centrifugal pumps, positive displacement pumps, and air compressors in water treatment, chemical processing, and pneumatic systems. Addresses the specific challenge of deadhead conditions and cavitation events that cause current spikes without immediate motor damage, allowing operators to investigate before catastrophic failure.

HVAC & Building Systems: Monitors chiller compressors, cooling tower fans, and air handling unit motors in commercial buildings and data centers. The relay's ambient temperature compensation (−25°C to +60°C) maintains accurate protection in rooftop installations and mechanical rooms with extreme seasonal variations.

Machine Tool Drives: Protects spindle motors, feed drives, and hydraulic pump motors in CNC machining centers, lathes, and milling machines. Fast trip response prevents tool breakage and workpiece damage when cutting tools encounter unexpected material hardness or fixturing failures.

Process Industry Equipment: Monitors mixer motors, agitator drives, and extruder motors in food processing, plastics manufacturing, and pharmaceutical production where product consistency depends on maintaining precise motor speeds under varying viscosity loads.

Technical Parameters & Selection Guide

Selection Criteria: Match the relay's adjustment range to your motor's nameplate full-load amperage (FLA). For motors rated 40-50A FLA, this model provides optimal protection. If your motor operates with a service factor above 1.0, set the dial to the actual running current rather than nameplate FLA. For motors outside this range, consult the 3RU11 series selection chart—smaller motors require 3RU1126 or 3RU1136 models with lower ranges, while larger motors need 3RU1146 variants.

Extended Functions

Remote Monitoring Integration: The auxiliary contacts interface with SCADA systems, PLCs, and building management systems to provide real-time trip status indication. Connect the NO contact to your control system's digital input for alarm notification and the NC contact for permissive interlocking in sequential start applications.

Test Function: Built-in test button simulates overload trip condition without disconnecting motor power, enabling commissioning verification and periodic functional testing to satisfy preventive maintenance protocols and insurance requirements.

Thermal Memory: After trip events, the bimetal elements retain heat proportional to the overload severity, preventing immediate restart attempts that could damage motors still above safe operating temperature. Memory duration ranges from 2-10 minutes depending on overload magnitude.

Modular Expansion: Add 3RU1900 auxiliary contact blocks to expand signaling capability up to 4 NO + 4 NC contacts for complex control schemes requiring multiple alarm circuits, remote/local indication, or redundant safety interlocks.

Delivery & Service Assurance

Standard Lead Time: In-stock units ship within 24-48 hours via express courier. Typical delivery to major industrial centers: 3-5 business days domestic, 7-12 days international. Expedited same-day shipping available for critical breakdown situations.

Warranty Coverage: 12-month manufacturer warranty against defects in materials and workmanship from date of purchase. Warranty includes free replacement and covers return shipping costs. Extended warranty programs available for high-reliability applications.

Technical Support: Access to application engineers for sizing verification, wiring diagrams, and troubleshooting assistance. Support available via email, phone, and remote video consultation during business hours (GMT+8, 9:00-18:00 weekdays).

Documentation Package: Each relay includes installation instructions, dimensional drawings, wiring diagrams, and trip characteristic curves. Downloadable CAD models, BIM objects, and EPLAN macros available for design integration.

Frequently Asked Questions

Q: How do I wire this overload relay for three-phase motor protection?
A: Connect the three motor supply phases (L1, L2, L3) to the relay's input terminals (1, 3, 5) and the outputs (2, 4, 6) to the motor terminals. Wire the auxiliary contacts to your control circuit for trip indication. Detailed wiring diagrams are included with each unit.

Q: What current setting should I use for a motor with 1.15 service factor?
A: Set the dial to the motor's actual operating current under normal load, not the nameplate FLA. If your 46A motor typically runs at 50A with service factor, adjust the relay to 50A for optimal protection without nuisance trips.

Q: Can this relay protect motors operating on variable frequency drives?
A: Thermal overload relays are designed for across-the-line (DOL) and reduced-voltage starters. For VFD applications, use the drive's built-in electronic motor protection or add a separate motor protection relay designed for PWM waveforms.

Q: What's the difference between manual and automatic reset modes?
A: Manual reset requires an operator to press the reset button after investigating the trip cause—recommended for critical equipment and safety compliance. Automatic reset allows the relay to self-recover after cooling—suitable for remote pumps, fans, and unmanned installations.

Q: How often should I test the overload relay function?
A: Press the test button quarterly to verify trip mechanism operation. Annually, verify current setting accuracy using a calibrated ammeter during motor startup. Replace relays every 8-10 years or after 50,000 operations in high-cycle applications.

Q: Is this relay compatible with single-phase motors?
A: While engineered for three-phase applications, you can protect single-phase motors by routing the phase conductor through all three poles in series, providing enhanced sensitivity. However, dedicated single-phase overload relays offer better performance for this application.

Take the Next Step

Protect your motor investments with proven Siemens thermal overload technology. Contact our technical sales team for application-specific sizing, volume pricing, or integration support for your motor control project. Request a quote today or add to cart for immediate checkout with secure payment processing.

© 2026 NINERMAS COMPANY LIMITED. All rights reserved.
Original Source: https://ninermas.com
Contact: sale@ninermas.com | +0086 187 5021 5667