What types of breakers should be used to protect motors?

When it comes to protecting motors, the selection of the right type of circuit breaker is crucial. In short, motor protective circuit breakers come in two primary types: thermal and magnetic.

Thermal breakers use a bimetallic strip to detect overloads in the motor circuit. The strip heats up with the overload and bends, activating the circuit breaker mechanism. Thermal breakers are designed to protect against sustained overloads, but are not effective when it comes to short-circuit protection.

Magnetic breakers, on the other hand, respond to high current surges that occur from short circuits. They use a magnetic mechanism to trip the circuit breaker, offering fast-acting protection against catastrophic failures.

So, which type of breaker should you use? The answer is, both.

For maximum protection, it is recommended that motors are equipped with both thermal and magnetic breakers. Thermal breakers should be sized to protect against sustained overcurrents (usually 125% of the motor's rated full-load amperage), while the magnetic breaker should be sized to protect against short-circuits (usually 250% of the motor's rated full-load amperage).

It's important to note that when selecting circuit breakers for motor protection, it's imperative to follow the manufacturer's recommendations. Motor manufacturers will typically specify the minimum and maximum amperage ratings for the thermal and magnetic breakers, as well as the appropriate trip curves to use. Using the wrong type of breaker can result in inadequate protection, false tripping, or even motor failure.

In summary, when it comes to protecting motors, thermal and magnetic breakers are both important for comprehensive protection. When selecting breakers, make sure to follow the manufacturer's recommendations and select the appropriate sizes and trip curves for your motor application.