Schneider Electric TeSys LRD Thermal Overload Relay User Manual

1. Introduction and Overview

The Schneider Electric TeSys LRD Thermal Overload Relay, model LR-D08, is a robust and reliable device designed for the protection of AC circuits and motors. It safeguards against overload, phase failure, and prolonged starting times, ensuring the operational integrity and longevity of industrial electrical equipment. This relay is rated for a current range of 2.5-4 Amperes and features a Class 10A trip characteristic, indicating a fast trip response time.

This manual provides essential information regarding the installation, operation, maintenance, and troubleshooting of your TeSys LRD08 thermal overload relay.

2. Safety Information

WARNING: Risk of Electric Shock and Injury.

• Installation, wiring, and maintenance of this device must only be performed by qualified and authorized electrical personnel.
• Always disconnect and lock out all power sources before performing any work on the relay or connected equipment.
• Ensure that all local and national electrical codes and regulations are strictly followed during installation and operation.
• Do not operate the device if it appears damaged or has been subjected to excessive stress.
• Verify correct wiring and current settings before energizing the circuit.

3. Product Features and Components

The TeSys LRD08 relay is designed for direct mounting to TeSys D contactors or standalone DIN rail mounting. Key features include:

• Adjustable thermal overload protection (2.5-4A).
• Phase failure sensitivity.
• Automatic reset function.
• Test button for trip simulation.
• Stop button for manual tripping.
• Reset button for manual reset.
• Screw clamp terminals for secure wiring.

Figure 3.1: Front view of the LRD08 relay, highlighting the current adjustment dial, blue RESET button, and red STOP button.

Figure 3.2: Side view displaying product labels, certifications (CE, EAC), and electrical ratings.

Figure 3.3: Side view illustrating the main power terminals (2T1, 4T2, 6T3) and auxiliary contact terminals (97NO, 98NO, 95NC, 96NC).

4. Setup and Installation

The TeSys LRD08 relay can be mounted directly to a compatible TeSys D contactor or independently on a DIN rail.

4.1. Mounting

• Direct Mounting: Align the three power terminals (top side of the relay) with the corresponding terminals on the bottom of the TeSys D contactor. Push firmly until the relay clicks into place.
• DIN Rail Mounting: For standalone applications, use an appropriate mounting adapter (not included) to secure the relay to a standard 35mm DIN rail. Ensure the relay is securely latched onto the rail.

Figure 4.1: Bottom view of the LRD08 relay, showing the integrated clip for direct contactor mounting or use with a DIN rail adapter.

4.2. Wiring

The LRD08 uses screw clamp terminals for electrical connections. Ensure all connections are tight to prevent overheating and poor contact.

• Main Power Circuit: Connect the motor's power leads to the main terminals (2T1, 4T2, 6T3) on the bottom of the relay. The incoming power from the contactor connects to the top terminals (L1, L2, L3) of the relay (when direct mounted).
• Control Circuit: Connect the auxiliary contacts (97NO, 98NO, 95NC, 96NC) into your motor control circuit. Typically, the normally closed (NC) contacts (95-96) are used in series with the contactor coil to provide trip indication and stop the motor upon overload. The normally open (NO) contacts (97-98) can be used for alarm or indication purposes.

Refer to the wiring diagram provided with your contactor or system for specific connection details.

5. Operating Instructions

5.1. Current Setting

Rotate the black dial on the front of the relay to set the desired motor full-load current (FLC) within the 2.5-4 Ampere range. Set the dial to match the motor's nameplate FLC. This setting determines the trip threshold for overload protection.

5.2. Reset Function

• Automatic Reset: The LR-D08 is configured for automatic reset (indicated by 'A' on the dial). After a trip due to overload, the relay will automatically reset once the bimetallic strips cool down, allowing the contactor to re-engage if the control circuit permits.
• Manual Reset: To manually reset the relay after a trip, press the blue 'RESET' button on the front of the unit. This is typically done after identifying and resolving the cause of the overload.

5.3. Stop Function

Press the red 'STOP' button on the front of the relay to manually trip the overload relay. This will open the normally closed (NC) contacts (95-96), de-energizing the contactor coil and stopping the motor. This function can be used for emergency stops or testing.

5.4. Test Function

The small 'TEST' button (often recessed) allows for a mechanical trip test of the relay's mechanism without applying actual overload current. Pressing this button simulates an overload trip, verifying the functionality of the auxiliary contacts and the tripping mechanism.

6. Maintenance

The TeSys LRD08 relay is designed for minimal maintenance. However, periodic checks are recommended to ensure optimal performance and safety.

• Visual Inspection: Regularly inspect the relay for any signs of physical damage, discoloration, or loose connections.
• Cleaning: Keep the relay free from dust, dirt, and moisture. Use a dry, soft cloth for cleaning. Do not use solvents or abrasive cleaners.
• Connection Check: Periodically verify that all screw terminals are tight and that wires are securely connected. Loose connections can lead to overheating and malfunction.
• Function Test: Periodically use the 'TEST' button to ensure the tripping mechanism is functional.

Always disconnect power before performing any maintenance.

7. Troubleshooting

If the TeSys LRD08 relay trips unexpectedly or fails to operate correctly, consider the following:

7.1. Relay Trips Frequently

• Overload Condition: The most common cause. Check the motor's current draw against its nameplate FLC. Ensure the relay's current setting matches the motor's FLC. Investigate if the motor is genuinely overloaded due to mechanical issues, voltage fluctuations, or incorrect sizing.
• Incorrect Current Setting: Verify the current setting dial is correctly set to the motor's full-load current.
• Phase Imbalance/Failure: Check for voltage imbalance or a lost phase in the supply to the motor.
• High Ambient Temperature: If the relay is in an excessively hot environment, it may trip prematurely. Ensure adequate ventilation.
• Damaged Relay: If all other causes are ruled out, the relay itself might be faulty and require replacement.

7.2. Relay Does Not Trip on Overload

• Incorrect Current Setting: The setting might be too high for the actual motor current.
• Wiring Error: Ensure the main power leads pass correctly through the relay's sensing elements.
• Faulty Relay: The internal mechanism may be damaged. Perform a 'TEST' button check. If it still doesn't trip, replace the relay.

7.3. Relay Does Not Reset

• Still Overloaded: The overload condition might still be present, preventing reset.
• Insufficient Cooling Time: For automatic reset, allow sufficient time for the bimetallic strips to cool down after a trip.
• Mechanical Jam: The internal reset mechanism might be jammed. Try pressing the manual reset button firmly.

8. Specifications

9. Warranty and Support

Specific warranty details for the Schneider Electric TeSys LRD08 Thermal Overload Relay are not provided within this document. For comprehensive warranty information, please refer to the official Schneider Electric website or contact their customer support directly.

For technical support, product inquiries, or service, please visit the official Schneider Electric website or contact their authorized distributors. Always provide the model number (LRD08) and any relevant serial numbers when seeking support.