Chint Thermal Overload Relay NXR-38

The Chint thermal overload relay NXR38 is a core product specifically designed for the overload protection of AC motors, and it is widely applied in fields such as industrial automation and mechanical equipment control. The following is a detailed analysis from aspects including technical parameters, functional features, application scenarios, installation and maintenance, and purchase suggestions:

Core Technical Parameters and Functional Features

1. Protection Capability

Setting Current Range: It covers 23A38A and supports fine adjustment, adapting to motors of different powers (for example, under a voltage of 380V, it can be matched with a threephase asynchronous motor of approximately 15kW).

Tripping Characteristics

Overload Protection: It will operate within 2 hours when the current is 1.2 times the setting current, and within 2 minutes when it is 1.5 times.

Phase Loss Protection: When the current of any two phases is 1.0 times and the current of the third phase is 0.9 times, it will operate within 2 hours.

Voltage Range: It supports AC circuits with a voltage range of 220V~690V, and is compatible with the mainstream power grid standards globally.

2. Structural Design

Installation Method: It supports plugin installation with NXC series contactors (such as the NXC38 contactor), or independent installation through a rail/screw, saving space in the power distribution cabinet.

Wiring Specifications: M4 screws are used for the main circuit, and the recommended wire crosssectional area is 2.5~6mm²; M3.5 screws are used for the auxiliary contacts, which are suitable for wires with a crosssectional area of 0.5~1.5mm², and the tightening torques are 1.7N·m and 0.8N·m respectively.

Protection Level: IP20 (protection against electric shock on the front side), suitable for conventional industrial environments.

3. Intelligent Functions

Temperature Compensation: With a builtin bimetallic strip structure, it automatically corrects the influence of the ambient temperature (5℃~+40℃) on the protection characteristics.

Reset Mode: It supports manual reset (using the RESET button) and automatic reset (which needs to be set through a knob), avoiding the risk of accidental restart.

Testing and Indication: It is equipped with a TEST button that can simulate an overload action. After tripping, the red indicator light will turn on, facilitating quick location of faults.

1. Typical Application Scenarios
2. Industrial Motor Control

It is suitable for the motors of equipment such as water pumps, fans, and compressors, preventing the overheating of the windings caused by sudden changes in load or poor heat dissipation. For example, in a sewage treatment system, it can protect the submersible sewage pump motor with a voltage of 380V and a power of 15kW.

It cooperates with the NXC contactor to form an electromagnetic starter, realizing the frequent start and stop control of the motor.

2. Requirements in Special Environments

It supports extreme temperatures ranging from 35℃ to +70℃ (for a short time), and can be used in cold storage or hightemperature workshops. However, it should be noted that when the temperature exceeds the normal range, it may affect the protection accuracy.

It is suitable for areas with an altitude ≤ 2000m. Capacity reduction is required for use in highaltitude environments.

III. Key Points of Installation and Maintenance

1. Installation Steps

Cooperation with the Contactor: Insert the NXR38 into the top of the NXC contactor, ensure that the conductive rods are aligned, and tighten the fixing screws. If it is installed independently, at least 50mm of heat dissipation space needs to be reserved.

Wiring Specifications: Connect the main circuit to L1L3 according to the phase sequence, and connect the auxiliary contacts to the control circuit (the normally closed contacts are connected in series to the contactor coil circuit). It is recommended to use a yellowgreen twocolor grounding wire.

2. Parameter Settings

Setting Current Adjustment: Adjust the knob to align the scale with the rated current value of the motor (for example, the rated current of a 15kW motor is approximately 30A, corresponding to the 30A scale of the NXR38).

Reset Mode Selection: If automatic reset is required, adjust the knob to the “A” position; for the manual mode, adjust it to the “M” position.

3. Troubleshooting

False Tripping: It may be caused by a too small setting current or a too long motor starting time (>25 seconds). It is necessary to appropriately increase the setting current or add a starting delay module.

Contact Sticking: Check whether the load is shortcircuited, or replace the contact module (model NXR38/AX).

Indicator Light Not On: Test the onoff of the auxiliary contacts, or check whether the fuse in the control circuit is blown.

1. Purchase and Alternative Solutions
2. Model Comparison

NXR25: The setting current is 0.1~25A, suitable for small motors (such as those below 3kW).

NXR38: 23A38A, covering mediumpower motors (such as 5.5kW~18.5kW).

NXR100: 23A100A, suitable for large equipment (such as motors above 30kW).

2. Price and Channels

Market Price: The price of a single unit is approximately  yuan.

International Procurement: Users in the United States can query the authorized distributors through Chint, or contact CHINT USA (Whatsapp: 008613811255435).

1. Precautions
2. Cooperation with the Fuse: It is recommended to be matched with the RT16 series fuse (such as RT1663/32A) to achieve the coordination of shortcircuit protection and overload protection.
3. Maintenance Cycle: Check the tightness of the wiring terminals every month, clean the dust and test the tripping characteristics every six months to ensure reliability.
4. Certification Compliance: It has passed CCC and CE certifications and complies with the IEC 6094741 standard, and can be used for export equipment.

If you need to obtain a more detailed product manual or technical support, you can visit the local technical service center of Chint.