Not everyone knows the notes about thermal relays

Thermal relay concept

Thermal relays are devices widely used in electrical systems, specifically used to protect the system from the risk of overheating. With the continuous temperature monitoring function, the thermal relay will automatically disconnect the power supply or stop system operation when the temperature exceeds the allowable level, limiting the risk of fire. Not only that, it also prevents damage to the device, ensuring maximum safety for the system and users.

Common applications of thermal relays in life

In fact, the relay takes care of the function of automatically turning on and off and directly impacts the electrical system. Specifically:  

- With the same control signal, the relay is capable of switching current to different loads.  

- Relays provide safe isolation between the control circuit and the load circuit, even when using AC power.  

- This device also supports comprehensive monitoring of the electrical system and performs circuit breaker appropriately, ensuring effective and safe operation.  

Structure of thermal relay

Thermal relays are made up of three main components, each of which plays its own role to ensure effective operation:  

1. Thermal sensor: This is the core part of the thermal relay, placed near the device to be protected to measure material temperature. Thermal sensors are mainly of two types:  

 - Bimeter type: Uses a metal bar assembled from two different materials. When the temperature changes, the bimeter bar expands, causing a twisting motion to activate the relay.  

   - Thermoelectric type: Includes a pair of wires made from two different materials, operating based on the voltage difference when the temperature changes, thereby activating the relay.  

2. Signal converter: This part receives the signal from the thermal sensor and converts it into an electrical signal. This electrical signal determines when the starter needs to be activated. The converter is usually integrated as an electronic circuit in the relay.  

3. Starter: Responsible for activating or shutting down the system when the temperature exceeds the set threshold. This part receives a signal from the converter, then issues a command to turn off power or stop system operation to protect the device from overheating and avoid dangerous incidents..  

Classification of popular thermal relays today:

Thermal relays are important devices used to protect electrical equipment from overheating. Below are some common types of thermal relays and their applications:  

- Single-phase thermal relay: Suitable for single-phase electrical systems, often used in household appliances such as fans, lights, refrigerators, and coolers to ensure safety when used.  

- 3-phase thermal relay: Designed for large-capacity electrical equipment using 3-phase power, such as air compressors and industrial pumps, to help protect the system from problems caused by thermal overload.  

- Thermal relay for rice cookers: Used to prevent overheating when cooking, ensuring durability and safety for the rice cooker.  

- high quality, reasonable price, used in booster pumps, submersible pumps, or pressure compensation pumps, protecting the pumping system during operation.  

- Water heater thermal relay: Used to control and limit the temperature of the water heater, avoiding dangerous overheating.  

- Iron thermal relay: Integrated in irons to protect the device from overheating, while also helping to save energy when in use. 

Instructions for choosing a suitable thermal relay  

To ensure the system operates stably and safely, choosing the right thermal relay is very important. Here are the factors to consider:  

- Overload current of the device: This is the most important factor to determine. Thermal relays must meet the overload current level that the device needs to protect. If chosen incorrectly, the device will not be properly protected, leading to damage or danger to the user.  

- Overload temperature value: This value needs to be adjusted appropriately. If set too low, the relay will activate continuously, causing interruption of operation. If placed too high, the device will not be protected promptly, increasing the risk of incidents such as fire, explosion or electric shock.  

- Relay operation method: Depending on protection requirements, you can choose a relay to operate immediately (turn off immediately when an overload occurs) or operate delayed (wait a certain time before turning off).  

- Power voltage: Make sure that the power voltage is compatible with the relay's operating voltage range to avoid problems during use  

- Type of thermal relay: Depending on the device to be protected, choose the appropriate type of relay. For example, a relay for a water pump will be different from a relay for a fan or an iron. 

Refer to technical specifications of thermal relays at:

LS thermal relay

Siemens thermal relay

Schneider thermal relay

See more at: Thermal relay