What is a Thermal Relay?

What is a  Thermal Relay?

Thermal relay definition

A thermal relay is defined as a device that uses unequal expansion rates of metals in a bimetallic strip to detect overcurrent conditions.

Working principle

Thermal relays work by heating a bimetallic strip, causing it to bend and close the normally open contact, which triggers the circuit breaker.

Construction of thermal relay

It consists of a bimetallic strip, metal with different expansion coefficients, a heating coil and contacts.

Technical parameter

• Rated voltage

• Rated current

• Rated frequency

• Set the current range

Delay function

The heating effect of the relay follows Joule's law, resulting in a delay in operation, allowing temporary overload without tripping.

Install

When the thermal relay is installed with other electrical appliances, it should be installed under the electrical appliances and more than 50mm away from other electrical appliances, so as not to be affected by the heating of other electrical appliances.

Routine maintenance

• It takes a certain amount of time to reset the thermal relay after operation, the automatic reset time should be completed within 5 minutes, and the manual reset button can be pressed after 2 minutes.

• After a short circuit fault occurs, check whether the thermal element and bimetal sheet are deformed

• Thermal relays in use should be checked once a week

• The thermal relay in use should be serviced once a year

Apply

Thermal relays are used for overload protection, especially in electric motors, where they prevent tripping due to short-term overload.