Schneider Electric LRN32N Thermal Overload Relay English Instruction Manual

Document Information

文書番号: EASY-D3N-LRN-EN-01

バージョン: 1.0

Date: January 14, 2026

言語: 英語

製品シリーズ: EasyPact D3N

1. 製品概要

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 主な特長

2. 技術仕様

2.1 Electrical Characteristics

2.2 環境条件

2.3 機械的特性

3. 動作原理

3.1 Core Components

1. Bimetallic Strip: Two metals with significantly different thermal expansion coefficients bonded together (the heart of the thermal overload protection mechanism)
2. Heating Element (Resistance Wire): Connected in series with the motor main circuit, generates heat proportional to the square of current (Joule’s Law)
3. Mechanical Tripping Mechanism: Triggered by bimetallic strip deformation to open the auxiliary contacts
4. リセット機構: Manual/automatic reset selector and button
5. Trip Indicator: Visual indication when the relay has tripped

3.2 Overload Protection Working Principle

1. 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.
2. 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.
3. 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

4. Installation Instructions

4.1 Mounting Procedures

4.1.1 Direct Mounting on LC1N Contactors

1. Ensure the contactor is de-energized and isolated from the power supply
2. Align the LRN32N relay with the mounting clips on the top of the LC1N contactor
3. Push the relay firmly until it clicks into place
4. Verify secure mounting by gently pulling on the relay

4.1.2 DINレール取付

1. Use appropriate DIN rail mounting accessories (available separately)
2. Align the relay with the DIN rail (35mm規格)
3. 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 安全上の注意事項

1. De-energize and isolate the circuit before installation, wiring, or maintenance
2. Ensure all connections are tight and secure to prevent overheating
3. Do not exceed the rated voltage and current specifications
4. Maintain proper ventilation around the relay for effective heat dissipation
5. Use only genuine Schneider Electric accessories for mounting and wiring
6. Commissioning and Adjustment

5.1 Current Setting Procedure

1. Set the current adjustment dial to the motor’s rated current (で)
2. For motors with high starting currents, ensure the setting allows for the starting period without tripping
3. Verify the setting corresponds to the motor nameplate data

5.2 Reset Mode Selection

1. Locate the reset selector switch on the relay front face
2. Set to “あ” (自動) または “M” (マニュアル) according to application requirements
3. Test the selected reset mode after commissioning

5.3 Trip Test

1. After installation and wiring, perform a trip test to verify proper operation
2. 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

3. For automatic reset mode:

After tripping, wait for the relay to automatically reset (typically 5-10 分)

Verify the contactor can be re-energized

6. メンテナンスとトラブルシューティング

6.1 Maintenance Schedule

6.2 トラブルシューティングガイド

7. 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

8. 注文情報

Product Code: LRN32N

説明: サーマルリレー, 23A-32A, Class 10A, EasyPact D3N series

Accessories: DIN rail mounting kit (オプション), auxiliary contact modules (LANN series)