What Do A and H Mean in Chint Thermal Overload Relay NR2-25?

The Meaning of A and H in Chint Thermal Overload Relay NR2-25

The A and H markings on Chint thermal overload relay NR2-25 are reset mode selection indicators, which are used to set the reset mode after the relay trips due to overload protection:

UN: Stands for Automatic reset. Dopo uno scatto per sovraccarico, the relay will automatically return to its initial state when it cools down to the set temperature, without manual intervention.

H: Stands for Hand reset. Dopo uno scatto per sovraccarico, the relay can only be reset by manually pressing the reset button, which prevents safety accidents caused by automatic restart of equipment before the fault is eliminated.

Reset Mode Switching Method

The reset mode of NR2-25 is switched via a blue knob:

1. Press the blue reset button with a screwdriver and rotate it clockwise.
2. Rotate A to the top position: Set to automatic reset mode.
3. Rotate H to the top position: Set to manual reset mode.

Application Scenario Recommendations

All thermal overload relays in Chint NR2 series are equipped with functions such as temperature compensation, trip indication, automatic/manual reset switching and shutdown, among which reset mode selection is one of the core operations.

Overview of Recommended Thermal Overload Relay Brands Besides Chint

In addition to Chint, mainstream thermal overload relay brands on the market are divided into two categories: international first-tier brands (advanced technology, stable quality) and high-quality domestic brands (cost-effective, suitable for local needs). Each has its own characteristics and applicable scenarios, with detailed recommendations as follows:

1. International First-tier Brands
2. Schneider Electric

Representative Series: LRD series (economic type), LRN series (standard type), LR9 series (heavy-duty type)

Core Advantages:

High trip accuracy and wide temperature compensation range (-25℃~+60℃), suitable for complex working conditions.

Equipped with complete functions such as phase failure protection, manual/automatic reset switching, and trip indication.

Perfectly compatible with LC1 series contactors, featuring convenient installation and low maintenance cost.

Applicable Scenarios: Large-scale factory automation, high-rise buildings, protection of critical equipment (per esempio., elevators, pompe dell'acqua)

2. Siemens

Representative Series: 3RV series (motor protection combination), 3UA series (traditional thermal overload relays)

Core Advantages:

German craftsmanship, with mechanical service life up to 10 million operations and electrical service life up to 5 milioni di operazioni, achieving excellent stability.

Strong anti-interference capability, suitable for high electromagnetic interference environments (per esempio., near frequency converters).

Supports thermal memory function to record overload history for easy fault analysis.

Applicable Scenarios: Precision manufacturing industry, chemical industry, metallurgy and other harsh industrial environments

3. ABB

Representative Series: TA series (standard type), Tmax series (integrated with circuit breakers)

Core Advantages:

Wide setting current range (0.1A~1000A), covering applications from micro motors to large-scale equipment.

Unique bimetallic strip design for fast and accurate overload response.

Can be seamlessly combined with ABB contactors and circuit breakers to form a complete protection solution.

Applicable Scenarios: Power systems, heavy machinery, new energy equipment (per esempio., wind power, photovoltaic)

4. Eaton (including Moeller)

Representative Series: ZB series (standard type), ZM series (modular type)

Core Advantages:

Inherited German technology, with excellent anti-vibration performance (compliant with IEC 60068-2-6 standard).

Equipped with tamper-proof protection to prevent safety hazards caused by incorrect setting.

Modular design supporting DIN rail mounting, saving control cabinet space.

Applicable Scenarios: Automobile manufacturing, port machinery, mining equipment and other high-vibration environments

5. Omron

Representative Series: TH-N series, TH-K series

Core Advantages:

Japanese precision manufacturing, with trip error <±5% and high protection accuracy.

Dimensioni compatte, suitable for high-density installation in control cabinets.

Forms a complete control link with Omron PLCs, relays and other products, featuring good compatibility.

Applicable Scenarios: Electronic manufacturing, food packaging, small-scale automation equipment

1. High-quality Domestic Brands (Cost-effective Options)
2. Delixi Elettrico

Representative Series: JR36 series (traditional type), JRS3 series (new type)

Core Advantages:

Price is only 1/3~1/2 of international brands, with performance close to international standards.

Adapted to the characteristics of domestic power grids, with strong resistance to voltage fluctuations.

Provides 3-year warranty with a sound after-sales service network and fast response.

Applicable Scenarios: Production lines of small and medium-sized enterprises, civil buildings, general industrial equipment

2. People Electric Appliance

Representative Series: JR20 series (heavy-duty type), JRS5 series (economic type)

Core Advantages:

Strong short-circuit withstand capability, able to withstand 6 times the rated current impact.

Adopts silver alloy contacts with good conductivity and arc oxidation resistance.

Supports manual/automatic reset switching for convenient operation.

Applicable Scenarios: Construction sites, agricultural machinery, general equipment protection

III. Brand Comparison and Selection Recommendations

Punti chiave di selezione

1. Parametri motore corrispondenti: Ensure the setting current range of the thermal overload relay covers the rated current of the motor (usually 1.05~1.1 times the rated current).
2. Function Requirements: Select products with functions such as phase failure protection, thermal memory, manual/automatic reset according to application scenarios.
3. Installation Compatibility: Match the installation dimensions and electrical interfaces of contactors and circuit breakers.
4. Adattabilità ambientale: Select products with corresponding protection levels for high-temperature, high-humidity and vibration environments.