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Document Information
文書番号: EASY-D3N-LRN-EN-01
Version: 1.0
Date: January 14, 2026
Language: English
Product Series: EasyPact D3N
- Product Overview
1.1 General Description
の LRN32N Thermal Overload Relay is a member of the Schneider Electric EasyPact D3N series, designed specifically for overload and phase failure protection of three-phase induction motors. It operates on the principle of thermal deformation of bimetallic strips and is ideal for use with Schneider LC1N series contactors in various industrial applications.
1.2 Key Features
| Feature | Description |
| Current Setting Range | 23あ – 32あ (adjustable) |
| 保護機能 | Overload protection, phase failure (phase loss) protection |
| Trip Class | 10あ (IEC 60947-4-1 standard) |
| Reset Options | Manual/automatic reset selector switch |
| Temperature Compensation | -30C to +60C (stable protection performance across varying temperatures) |
| Contact Configuration | 1 normally closed (ノースカロライナ州) そして 1 normally open (いいえ) auxiliary contact |
| Mounting | Direct mounting on LC1N contactors or DIN rail installation |
| 寸法 | 70mm * 45mm (height width) |
| コンプライアンス | IEC 60947-4-1, GB14048 standards |
- Technical Specifications
2.1 Electrical Characteristics
| パラメータ | Value | Standard |
| Rated Operational Current (Ie) | 32あ | IEC 60947-4-1 |
| Setting Current Range (Ir) | 23あ – 32あ | IEC 60947-4-1 |
| Trip Class 10A Characteristics | 1.05 × Ir: No trip for ≥ 2 hours | IEC 60947-4-1 |
| 1.2 × Ir: Trip time 20-60 秒 | ||
| 1.5 × Ir: Trip time 2-10 秒 | ||
| 7.2 × Ir: Trip time ≤ 0.5 秒 | ||
| Rated Insulation Voltage (Ui) | 690V AC | IEC 60947-4-1 |
| Rated Operational Voltage (うえ) | Up to 690V AC | IEC 60947-4-1 |
| Auxiliary Contact Rating | 250V AC, 5あ (resistive load) | IEC 60947-5-1 |
| Dielectric Strength | 6kV at 50Hz | IEC 60947-4-1 |
2.2 Environmental Conditions
| Condition | Range | |
| 動作温度 | -30°C to +60°C (no derating) | |
| Storage Temperature | -60°C to +80°C | |
| Relative Humidity | 5% に 95% (non-condensing) | IEC 60068-2-78 |
| 高度 | ≤ 2000m (no derating) | IEC 60947-4-1 |
2.3 Mechanical Characteristics
| パラメータ | Value |
| 重さ | 0.12kg |
| Mechanical Life | ≥ 10,000 operations |
| Electrical Life | ≥ 1,000 operations at rated load |
| Reset Time (Automatic) | 5-10 minutes (after tripping) |
| Reset Time (Manual) | Immediate (after bimetallic strip cooling) |
- Operating Principle
3.1 Core Components
- Bimetallic Strip: Two metals with significantly different thermal expansion coefficients bonded together (the heart of the thermal overload protection mechanism)
- Heating Element (Resistance Wire): Connected in series with the motor main circuit, generates heat proportional to the square of current (Joule’s Law)
- Mechanical Tripping Mechanism: Triggered by bimetallic strip deformation to open the auxiliary contacts
- Reset Mechanism: Manual/automatic reset selector and button
- Trip Indicator: Visual indication when the relay has tripped
3.2 Overload Protection Working Principle
- Normal Operation: When motor current is within the setting range (23A-32A), the heating element produces limited heat, causing minimal bimetallic strip deformation. The relay remains in the closed state, allowing the motor to run normally.
- Overload Condition: When motor current exceeds the setting value (例えば, due to excessive load or locked rotor), the heating element’s temperature rises rapidly (heat ∝ I²Rt). The bimetallic strip bends toward the metal with the lower thermal expansion coefficient.
- Tripping Action: When the bending reaches a threshold (dependent on current magnitude and duration as per Trip Class 10A), the mechanical tripping mechanism activates, opening the NC auxiliary contact. This cuts power to the contactor coil, which in turn disconnects the motor from the main power supply.
3.3 Phase Failure Protection Principle
Phase failure protection operates based on unbalanced three-phase current detection:
Normal Condition: Balanced three-phase currents produce equal heat in all three heating elements, resulting in uniform bimetallic strip deformation.
Phase Loss Condition: When one phase is lost, the remaining two phases carry approximately 1.73 times the normal current, causing uneven heating and accelerated bending of the corresponding bimetallic strips. This triggers tripping faster than in a simple overload situation.
3.4 Reset Mechanism Operation
| Reset Mode | Operation | Application |
| Automatic Reset | After tripping and power disconnection, the bimetallic strip cools and returns to its original shape, automatically resetting the relay. The NC contact closes when the bimetallic strip has sufficiently cooled. | Applications where automatic restart is permissible after fault clearance |
| Manual Reset | After tripping, the relay remains in the tripped state even when the bimetallic strip cools. Manual intervention (pressing the reset button) is required to reset the relay. | Applications where accidental automatic restart must be prevented |
- Installation Instructions
4.1 Mounting Procedures
4.1.1 Direct Mounting on LC1N Contactors
- Ensure the contactor is de-energized and isolated from the power supply
- Align the LRN32N relay with the mounting clips on the top of the LC1N contactor
- Push the relay firmly until it clicks into place
- Verify secure mounting by gently pulling on the relay
4.1.2 DIN Rail Mounting
- Use appropriate DIN rail mounting accessories (available separately)
- Align the relay with the DIN rail (35mm standard)
- Snap the relay onto the rail until it locks securely
4.2 Wiring Diagram
4.2.1 Power Circuit Connection
Connect the three-phase motor main circuit through the LRN32N main terminals (1, 2, 3 for input; 4, 5, 6 for output)
Ensure correct phase sequence (L1→1, L2→2, L3→3; 4→U, 5→V, 6→W)
4.2.2 Control Circuit Connection
Connect the NC auxiliary contact (95-96) in series with the contactor coil circuit
The NO auxiliary contact (97-98) can be used for alarm or status indication purposes
Use appropriate wire sizes: 1.5-10mm² for power circuits, 1-2.5mm² for control circuits
4.3 Safety Precautions
- De-energize and isolate the circuit before installation, wiring, or maintenance
- Ensure all connections are tight and secure to prevent overheating
- Do not exceed the rated voltage and current specifications
- Maintain proper ventilation around the relay for effective heat dissipation
- Use only genuine Schneider Electric accessories for mounting and wiring
- Commissioning and Adjustment
5.1 Current Setting Procedure
- Set the current adjustment dial to the motor’s rated current (で)
- For motors with high starting currents, ensure the setting allows for the starting period without tripping
- Verify the setting corresponds to the motor nameplate data
5.2 Reset Mode Selection
- Locate the reset selector switch on the relay front face
- Set to “あ” (Automatic) または “M” (Manual) according to application requirements
- Test the selected reset mode after commissioning
5.3 Trip Test
- After installation and wiring, perform a trip test to verify proper operation
- For manual reset mode:
Increase the motor load until the relay trips (or use a test button if available)
Verify the contactor disconnects the motor
Press the reset button to restore operation
- For automatic reset mode:
After tripping, wait for the relay to automatically reset (typically 5-10 minutes)
Verify the contactor can be re-energized
- Maintenance and Troubleshooting
6.1 Maintenance Schedule
| Task | Frequency | Procedure |
| Visual Inspection | Monthly | Check for loose connections, overheating signs, and damage |
| Cleaning | Quarterly | Remove dust and debris with a dry cloth or soft brush (de-energized) |
| Function Test | Annually | Perform trip test to verify protection functionality |
| Calibration Check | Every 2 years | Verify current setting accuracy with a clamp meter |
6.2 Troubleshooting Guide
| Symptom | Possible Cause | Solution |
| No tripping during overload | 1. Current setting too high | 1. Adjust setting to motor rated current |
| 2. Heating element damaged | 2. Replace heating element | |
| 3. Bimetallic strip fatigued | 3. Replace bimetallic strip or relay | |
| 4. Tripping mechanism blocked | 4. Clean and lubricate mechanism | |
| Unintentional tripping | 1. Current setting too low | 1. Adjust setting appropriately |
| 2. Poor ventilation/overheating | 2. Improve ventilation | |
| 3. Unbalanced three-phase current | 3. Check for phase loss or unbalanced load | |
| 4. Voltage fluctuations | 4. Install voltage stabilizer if needed | |
| Failed reset | 1. Reset mechanism damaged | 1. Replace reset mechanism or relay |
| 2. Bimetallic strip not cooled sufficiently | 2. Wait for complete cooling (5-10 minutes) | |
| 3. Contactor fault | 3. Check and repair contactor | |
| Auxiliary contacts not working | 1. Contact oxidation | 1. Clean or replace contacts |
| 2. Wiring errors | 2. Verify correct wiring | |
| 3. Mechanical damage | 3. Replace damaged parts or relay |
- Safety Information
7.1 Warnings and Cautions
RISK OF ELECTRIC SHOCK: Always de-energize and lock out/tag out the circuit before working on the relay
RISK OF FIRE: Ensure proper wire sizing and tight connections to prevent overheating
Do not bypass the overload protection under any circumstances
Use only genuine Schneider Electric replacement parts to maintain safety and performance
Follow local electrical codes and regulations during installation and operation
7.2 Disposal Instructions
– Dispose of the relay in accordance with local environmental regulations
– Separate plastic components from metal parts for recycling
– Do not dispose of in regular household waste
- Ordering Information
Product Code: LRN32N
Description: Thermal Overload Relay, 23A-32A, Class 10A, EasyPact D3N series
Accessories: DIN rail mounting kit (optional), auxiliary contact modules (LANN series)
