Thermal overload relays sense motor current by converting this current to heat in a resistance element. The heat generated is used to open a normally closed contact in series with a starter coil causing the motor to be disconnected. Thermal overload relay has many advantages and disadvantages. Let’s check them one by one.
Advantages of Thermal Overload Relay
The benefits of a thermal overload relay are:
- It protects the motor from overheating. It can be used in 1 or 3-phase motors.
- Some overload relays have internal phase loss protection.
- It has an effective operating principle.
- It is a low-cost device.
- It can be mounted directly to a contactor or it can be mounted to the panel with a DIN rail adaptor.
- It has an internal test button used for troubleshooting.
- Some overload relays have an internal trip class selection button.
- It has a wide and adjustable current range.
- It has a reset function. (manual or automatic)
- It has a temperature compensation feature.
- It has a trip-free mechanism.
Disadvantages of Thermal Overload Relay
The drawbacks of a thermal overload relay are:
- It does not have a direct breaking function. It should be used with other switching or protection devices to disconnect the circuit.
- It does not have short-circuit protection.
- It is slow in operation.
- It does not have a high switching frequency. Cooling is necessary after numerous tripping.
- It does not perform well in heavy-duty starting.
- It does not withstand vibration and shock. (Only some special types can perform well)
In conclusion, thermal overload relays are a popular choice for protecting motors from overheating and they offer several advantages such as effective operating principle, low cost and wide current range. They also have useful features like temperature compensation and a trip-free mechanism. However, they also have some disadvantages such as the lack of direct breaking function, short-circuit protection and slow operation. Additionally, they may not be suitable for heavy-duty starting, and cooling is necessary after numerous tripping. Nevertheless, the benefits of thermal overload relays make them a practical solution for protecting motors from overheating and their disadvantages can be mitigated by using them in combination with other protective devices.
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