Chint Thermal Overload Relay NR2-257-10A

Chint Thermal Overload Relay NR2-257-10A is a product in the NR2 series, mainly used for overload and phase-failure protection of AC motors.

I. Technical Parameters and Functional Characteristics*Chint Thermal Overload Relay JR36-63/28A-45A*

1. Basic Parameters

- **Rated Current Range**: 7-10A, suitable for motor protection where the setting current falls within this range.

- **Frame Current**: 25A, which belongs to the medium current specification in the NR2 series and is compatible with contactor models such as NC1/CJX2-09-32.

- **Voltage Range**: Supports AC circuits with 50Hz/60Hz frequency and voltage up to 690V, complying with international and Chinese standards including IEC 60947-4-1 and GB/T 14048.4.

- **Trip Class**: 10A, with an operating time that meets industry standards to ensure rapid circuit interruption in case of overload.

2. Core Functions

- **Overload Protection**: Monitors current through a bimetallic strip structure and triggers tripping when the current exceeds the setting range.

- **Phase-Failure Protection**: Can detect the disconnection of any phase in a three-phase circuit and act within 2 hours.

- **Temperature Compensation**: Adapts to ambient temperatures ranging from -5°C to +40°C, ensuring stability under different working conditions.

- **Reset Method**: Supports both manual and automatic reset; the circuit can be restored by operating the button.

3. Structural Design

- **Installation Method**: Can be installed in combination with contactors (e.g., NC1/CJX2 series) or fixed via an independent mounting base (e.g., MB-2).

- **Wiring Specification**: The main circuit supports 1-2.5mm² wires, and the auxiliary circuit uses M3.5 screws, which are suitable for common industrial wiring requirements.

- **Status Indication**: After tripping, the trip status is displayed through a mechanical indicator window, facilitating quick fault diagnosis.

 II. Application Scenarios and Selection Recommendations

1. Typical Applications

- **Industrial Motor Control**: Suitable for motor protection of equipment such as machine tools, pumps, and fans, especially for loads that require frequent starting and stopping.

- **Automation Systems**: Can be combined with contactors and circuit breakers to form a complete motor control circuit, improving system reliability.

- **Civil Equipment**: Applicable to scenarios with high overload protection requirements, such as elevators and air-conditioning compressors.

2. Selection Notes

- **Current Matching**: The setting range should be selected based on the rated current of the motor. For example, a 7.5kW three-phase motor (approximately 15A) requires a larger-sized thermal overload relay (e.g., NR2-36).

- **Environmental Adaptability**: In high-temperature environments (such as boiler rooms), priority should be given to models with temperature compensation to avoid false tripping.

- **Certification Requirements**: When exporting to the North American market, it is necessary to confirm whether the product has passed UL certification (some Chint models have obtained UL certification, but the specific certification status of NR2-257-10A needs further verification).

 III. Installation and Maintenance Guidelines

1. Installation Steps

- **Combination Installation**: Insert directly into the thermal overload relay slot of the contactor and ensure the buckle is firmly locked.

- **Independent Installation**: Fix on the guide rail using the MB-2 mounting base, tighten the M4 screws, and pay attention to maintaining levelness.

- **Wiring Standards**: Connect the main circuit to L1/L2/L3 according to the phase sequence, and connect the auxiliary contacts (NO/NC) to the control circuit. Ensure the terminal torque meets the standard (reference value: 2.5N·m).

2. Commissioning Key Points

- **Setting Current Configuration**: Rotate the adjustment knob to align the scale with 1.05 times the rated current of the motor (e.g., set to 10.5A for a 10A motor).

- **Function Testing**: Press the test button to simulate an overload, observe whether tripping occurs within 2 minutes, and verify the effectiveness of the protection function.

3. Maintenance Recommendations

- **Regular Inspection**: Clean the dust on the housing quarterly, check if the wiring terminals are loose, and test the flexibility of the reset button.

- **Fault Diagnosis**: If frequent tripping occurs, check whether the motor is overloaded, the wiring is loose, or the setting value of the thermal overload relay is too low.

 IV. Alternative Models and Purchasing Channels

 1. Alternative Solutions

- **Same-Series Upgrade**: If higher current capacity is required, models such as NR2-36 (setting range 28-36A) or NR2-93 (30-40A) can be selected.

- **Cross-Brand Compatibility**: Siemens 3UA59 and ABB T-series thermal overload relays can be used as alternatives, but attention should be paid to differences in installation dimensions and wiring methods.

2. Procurement Information

- **Price Range**: The unit price is approximately 22-26 RMB. For bulk purchases, discounts can be obtained through channels such as 1688 and JD.com, or via WhatsApp: 0086-13811255435.

- **Certified Versions**: Some e-commerce platforms provide export models with CE certification; specific requirements should be specified when placing an order.

 V. Precautions and Compliance

1. Safety Standards

Grounding Requirements**: The metal housing must be reliably grounded (PE), and the grounding resistance should be less than 4Ω.

Isolation Operation**: Before replacing the thermal overload relay, be sure to cut off the upper-level power supply and test for electricity to avoid electric shock risks.

 2. International Compliance

- **UL Certification**: Chint Electric has obtained overall UL certification, but the specific certification status of NR2-257-10A needs to be confirmed by contacting the manufacturer. It is recommended to prioritize models with the UL mark (e.g., NR2-25/Z).

- **RoHS Directive**: The product complies with EU environmental protection requirements and is suitable for equipment exported to Europe.

VI. Summary

With its high cost-effectiveness and stable performance, NR2-257-10A is widely used in small and medium-sized motor protection scenarios. When selecting the model, users should focus on current matching, environmental adaptability, and certification requirements. During installation, wiring standards must be strictly followed, and regular maintenance should be conducted to ensure long-term reliable operation. For further technical support, detailed manuals and after-sales services can be obtained through the Chint official website or customer service channels.