The difference between thermal relay and motor protector - Solutions - Huaqiang electronic network

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When it comes to the difference between a bimetallic thermal relay and a motor protector, statistics show that out of 100 motor burnout incidents, 30 are caused by the failure of the thermal relay to function properly. The reasons vary, but one key issue is that traditional thermal relays have inherent limitations that can't be easily overcome. For instance, bimetallic elements are prone to thermal fatigue and may not return to their original state after repeated overheating. Because of this, many engineers avoid using thermal relays in the initial design of electromechanical systems.

Motor protectors have been used in China for over 30 years, yet motor burnouts still occur frequently. This is mainly due to three key issues: First, there's often confusion in product function design—what are the essential features, and what are just extra functions? (More features don’t always mean better performance.) Second, current sensors used in motor protectors aren’t ideal, leading to problems like false trips, poor compatibility with thermal relays, and limited adaptability to harsh environments. Third, users haven’t seen immediate benefits from these devices, which limits their adoption.

Over 97% of low-voltage motor failures are caused by overcurrent, which can result from overload, starting timeouts, phase loss, overvoltage, undervoltage, or poor contact in the three-phase lines. Overcurrent from overload or starting timeout causes a balanced increase in all three phases, while issues like phase loss or voltage imbalance cause an unbalanced rise in one or two phases. Therefore, high-precision sinusoidal current sampling is crucial for effective motor protection.

The damage caused by a burned-out motor isn’t just about repair costs. It can take time for mechanics to remove the damaged motor from the equipment, causing production delays. In critical industrial settings, motor failure can lead to significant indirect losses, such as increased maintenance costs and reduced product quality. Repaired motors often don’t perform as well as new ones, accelerating the depreciation of the entire system. With copper prices rising, protecting motors from burning has become even more important.

A small motor costing tens of thousands of yuan is not worth being protected by an unreliable thermal relay. These devices consume very little energy—around 20W for a small unit, up to 80–100W for larger models—but they offer minimal protection. In the past, when energy was abundant, efficiency wasn’t a priority. Today, with growing concerns about energy conservation and resource management, the need for a reliable motor protector is more urgent than ever. An ideal motor protector is not just a technical necessity—it’s a smart and responsible choice for modern industry.