LR2-D33 3-Phase Plug-In Thermal Overload Relay

Product Overview

The LR2-D33 series thermal overload relay is a bimetallic motor protection device designed for plug-in assembly with matching frame-size AC contactors, forming an integrated direct-on-line (DOL) motor starter. It protects 3-phase induction motors from damage caused by sustained overload current, single-phase loss and phase imbalance faults in low-voltage control and distribution systems.

Operating on the thermal deflection principle of bimetallic strips heated by load current, it delivers inverse-time tripping under overload conditions, with trip class 10 characteristics optimized for standard squirrel-cage motors. The built-in differential phase detection mechanism identifies phase loss and phase imbalance rapidly and trips before motor winding overheating occurs. It supports both automatic and manual reset modes, with integrated ambient temperature compensation to maintain accurate tripping across a wide operating temperature range. Equipped with 1 NO + 1 NC silver alloy auxiliary contacts for control interlocking and fault signaling. It is widely applied in motor control centers (MCC), pump & fan control panels, machinery OEM equipment and industrial building distribution systems.

Key Product Features

✅ Plug-In Direct Contactor Mounting Designed for direct plug-in assembly with same-frame CJX2 series AC contactors, forming a compact integrated motor starter. Eliminates interconnection wiring, saves cabinet space and reduces assembly labor. Also supports independent 35mm DIN rail mounting.

✅ Overload + Phase Failure Dual Protection Inverse-time thermal overload protection with continuously adjustable current setting, plus dedicated differential phase failure detection. Sensitive to single-phase fault, phase imbalance and phase reversal, effectively prevents motor burnout caused by asymmetrical operation.

✅ Ambient Temperature Compensation Integrated compensation bimetallic strip automatically offsets the effect of ambient temperature variation on tripping accuracy. Maintains stable tripping characteristics across -25℃ to +55℃, suitable for both indoor workshop and outdoor equipment applications.

✅ Auto / Manual Selectable Reset Supports both automatic self-reset and manual push-button reset. Automatic reset enables unattended recovery after temporary overload; manual reset requires operator confirmation before re-energizing, improving safety for maintenance scenarios. Integrated test button for on-site functional verification.

✅ 1NO + 1NC Silver Alloy Auxiliary Contacts Equipped with 1 normally open and 1 normally closed auxiliary contact with silver alloy contact points. Used for control circuit interlocking, self-holding, fault alarm output and remote status indication. Reliable electrical endurance for frequent switching operations.

✅ Clear Current Setting Dial Large easy-to-read current adjustment dial with clear scale marking. Enables precise setting of rated protection current on site, matching actual motor nameplate current for optimized protection.

✅ IEC 60947-4-1 International Standard Manufactured and fully type tested in accordance with IEC 60947-4-1 and GB/T 14048.4 standards. Passed overload tripping test, phase failure test, endurance test and dielectric withstand test, qualified for global industrial motor protection projects.

Technical Specifications

表格

Application Scenarios

• Direct-on-line (DOL) motor starters and motor control centers (MCC)
• Pump, fan, compressor and conveyor drive motor protection
• Machine tool, packaging machinery and production line control systems
• Industrial plant and commercial building motor control circuits
• HVAC, water treatment and agricultural equipment motor protection
• Panel builder and switchgear assembly OEM matching

Our Advantages

1. Accurate and stable tripping performance Precision calibrated bimetallic strips and transmission mechanism, accurate tripping current and inverse time characteristic, avoids nuisance tripping and failure to trip, ensures reliable motor protection.
2. Convenient plug-in assembly design Direct plug-in matching with same-frame contactors, no external wiring required between contactor and relay, reduces assembly time and cabinet space.
3. Strict factory quality inspection Each unit undergoes overload tripping calibration, phase failure response test, insulation test and mechanical life test before delivery to ensure consistent on-site performance.
4. High compatibility and interchangeability Standard mounting dimensions and terminal layout, fully compatible with mainstream LR2 / D series thermal overload relays on the market, easy for maintenance replacement.
5. Complete technical documentation support Provide dimension drawings, wiring diagrams, selection guides and test certificates to support project design, tender bidding and on-site commissioning guidance.

Custom Solution

We provide project-oriented custom solutions for thermal overload relays:

• OEM Brand Customization: Custom silk-screen logo and model marking on product housing and dial for distributor branded resale.
• Specification Customization: Custom current rating range, trip class and auxiliary contact configuration according to specific motor protection requirements.
• Reset Mode Customization: Fixed automatic or manual reset mode according to customer standard specifications.
• Export-grade Custom Packing: Neutral carton, customer-branded packaging, seaworthy reinforced packing for long-distance sea transportation.
• Large-order Priority Production: Priority production schedule for large machinery OEM and EPC project orders to guarantee delivery lead time.

Share your required current range, trip class and application scenario, our engineers will recommend the most suitable thermal relay solution within 24 working hours.

FAQ

Q1: What is a thermal overload relay used for?

A: A thermal overload relay protects 3-phase induction motors from damage caused by sustained overload current, phase loss and phase imbalance. It is almost always paired with an AC contactor to form a complete motor starter.

Q2: What does trip class 10 mean?

A: Trip class 10 means the relay will trip within 10 seconds when carrying 7.2 times the rated current. It is the standard trip class for general purpose squirrel cage induction motor protection.

Q3: Does this relay have phase failure protection?

A: Yes. It is equipped with a differential phase detection mechanism that sensitively detects single-phase faults and phase imbalance, and trips rapidly to protect the motor from burnout under asymmetrical operation.

Q4: What is the difference between auto and manual reset?

A: In automatic reset mode, the relay automatically resets after cooling down once the fault clears. In manual reset mode, an operator must press the reset button after confirming safety, which is preferred for maintenance and hazardous machinery scenarios.

Q5: How is this relay installed?

A: It is designed for direct plug-in mounting on matching frame-size AC contactors. It can also be installed independently on a standard 35mm DIN rail in control cabinets.

Q6: Do you support OEM private label service?

A: Yes, we support custom logo and model marking on the product. A certain minimum order quantity applies for OEM service.

Q7: What standard does this relay comply with?

A: It complies with IEC 60947-4-1 international standard for low-voltage controlgear, and meets general industrial motor protection requirements.

Package Content

1 × LR2-D33 Thermal Overload Relay