Which type of overload relay is commonly used in motor starters?

The correct choice is that all types of overload relays, including bimetallic, magnetic, and melting alloy, are commonly used in motor starters. Each type has distinct characteristics that can be beneficial depending on the application and motor protection requirements.

Bimetallic relays operate based on the thermal expansion of two different metals bonded together. When the motor experiences an overload and generates excess heat, the bimetallic strip bends and trips the relay, opening the circuit and protecting the motor from damage.

Magnetic relays, on the other hand, work on the principle of electromagnetic induction. When current flowing through the coil of the relay exceeds its rated level, the magnetic field generated can trigger the relay to trip, providing quick response to overload situations.

Melting alloy relays utilize a fusible metal that melts at a specific temperature when an overload occurs. This type of relay provides a distinct method of protection, as it physically breaks the circuit by melting.

Each of these overload relay types serves the purpose of protecting motors from excessive current, which can lead to overheating and potential damage, thus making them integral to motor starter applications.