A thermal relay (also known as an overload relay) is a commonly used safety device in electrical installations. It protects an electric motor from damage due to stalling, overload, long start-ups or phase failure. In addition to providing protection for the motor, the overload relay provides effective reading control. When does thermal protection operate and which thermal relay should you choose?
Check thermal relays at the Onninen wholesaler
What is an overload relay?
The overload relay is one of the key protections of electrical systems. It provides protection and control of the operation of motors, transformers, industrial furnaces and other electrical devices. It protects the motor from overheating, overload and failures caused by excessive current. It is essential in extreme working conditions. Additionally, the overload relay allows precise control of the electrical load. An increase in current above the permissible, safe level causes the overload relay to operate, which immediately switches off the power circuit, preventing damage to the contactor and the entire device. Installing overload relays is not a major challenge for an electrician. In most cases, they are connected directly to the working circuit and contactors.
How does a thermal relay work?
When the winding of an electric motor is heated, the thermal relay changes form and state, using the properties of bimetal (bimetal plates) for this purpose. The motor current flows through the resistors. When a certain temperature value is exceeded, e.g. due to a motor failure, the resistors cause the bimetal to heat up. Reaching the operating temperature leads to additional curvature of the plates, which turn off the thermal switch. At a critical moment, the working circuit is completely broken, so nothing dangerous will happen to the machine and the personnel.
How to select a thermal relay?
A properly matched thermal relay affects the safety and efficiency of work and the optimal life of devices. It protects not only machines, but also the people operating them. It allows to minimize the risk of downtime due to device failure. Therefore, the purchase of a relay should be carefully considered, and it is best to consult with an experienced electrician or another specialist familiar with the subject.
When choosing a thermal relay, you should pay attention to such parameters as:
- trigger class,
- current setting range,
- method of assembly,
- type of main contact connection,
- number and type of auxiliary contacts,
- maximum rated operating voltage (Ue),
additional functions.
In order to protect electric motors against overload, relays with a tripping class of 10A and 10 (light and traditional motor starting) are most often used. The rated current of the relay is selected to the rated current of the motor - this value must be within the range of the thermal relay current setting.
Relays in the Onninen wholesaler
In the Onninen electrical wholesaler you will find overload relays with various parameters and functions, which allows for precise selection of a protective device for the implemented project. We offer reliable and safe thermal relays from brands such as Eaton and Schneider Electric Polska. They enable effective, long-term protection of devices and precise control of the operation of the motor and entire electrical processes. Most thermal relays have a wide range of rated current adjustment and are intended for direct installation.