Thermal Relays: Choosing One to Match with Contactors
Thermal relays (motor overload protection) are usually used in conjunction with contactors. Manufacturers with high overlap in brand and model are mainly domestic brands such as Chint, Delixi, and Tianzheng, while Schneider Electric and ABB’s Chinese factories provide high-end product lines.
Industry insiders point out that the key to “which thermal relay manufacturer is the best” is not choosing one separately, but rather “matching the same brand as the contactor + matching the setting range”—the thermal relay and contactor should be installed together, and the same brand provides the best compatibility.
Recommended Manufacturers
- Chint Electric: Large shipment volume of thermal relays (JR36 series, etc.), complete supporting products, mainstream in industrial and civilian markets;
- Delixi, Tianzheng Electric: Complete thermal relay and contactor supporting system, high cost performance;
- Liangxin Shares: Mature industrial-grade thermal relay and electronic overload protection product lines;
- Schneider Electric, ABB China factories: High-end thermal relays (such as LRD series, electronic type), leading in setting accuracy and reliability, suitable for critical equipment;
- Yueqing Industrial Belt Supporting Factories: Numerous small and medium-sized factories provide supporting production, low prices, quality and certification need to be verified.
Key Points for Selection and Factory Selection
Firstly, compatibility with supporting components.
The thermal relay must be of the same brand or standard as the contactor, and the installation method (plug-in/independent), wiring terminals, and current rating must match. Priority should be given to purchasing the contactor and thermal relay as a complete set from the same brand.
Secondly, the setting range is crucial.
The rated current must cover the motor’s rated current (the setting range is adjustable). Incorrect selection can lead to malfunctions or failures to operate.
Thirdly, the tripping class is important.
Standard thermal relays (10A class) and fast-tripping relays (tripping classes 10/20, etc.) should be selected based on the starting load; this is especially important for motors that start frequently.
Fourthly, certification and lifespan are critical.
CCC certification, electrical life, and operating characteristics (type testing) are quality thresholds.
Fifthly, there is a trend towards electronic overload relays.
Electronic overload relays (phase loss, locked rotor protection) offer more comprehensive functions, and important circuits can be upgraded.
**Pitfalls to Avoid**
**Firstly, “generic brands sold as genuine products.”
Generic thermal relays use substandard bimetallic strip materials, leading to setting drift that can cause motor burnout or accidental shutdown.
Secondly, “refurbished parts mixed in batches.”**
Refurbished used parts entering the market should be inspected and verified against batch and appearance.
Thirdly, there is “false labeling of setting range.”
Setting range and tripping characteristics are often mislabeled; nameplates and test reports should be checked during acceptance.
Fourthly, there is “incompatible matching.”
Mixing brands of thermal relays and contactors leads to installation mismatches;
purchasing complete sets is more reliable.
Trends and Reminders
Thermal relays are moving towards “electronic + intelligent”: Electronic overload relays (with communication and fault recording) are becoming increasingly common in critical equipment, replacing traditional bimetallic thermal relays.
For buyers, it is recommended to “match the same brand as the contactor, ensure precise matching of setting range, and dual-core certification parameters,” and prioritize genuine brand products for motor protection circuits.
Thermal relays are the gatekeepers of motor safety;
choosing the right manufacturer ensures reliable overload protection.
