Basics of Circuit Breaker?

What is a circuit breaker?

Circuit breaker is a device designed to open and close a circuit using a non-automatic (manual) as well as opening the circuit (tripping) automatically at a predetermined over-current level,without injury to itself when properly applied within its rating.

Breaker Operation - Manual

Using the operating lever to open and close the circuit.

Breaker Operation - Automatic

Automatic breaker operation means over current protection.

Basic trip curve illustrate the relationship between response (trip) time and current.

Over load Condition- excessive current condition resulting from an increase in the load applied (beyond set limit).

Correlates to the first part of the curve (L - Long delay)

During an overload,the excessive current through the breaker will generate heat.

The greater the overload condition,the greater the current and the greater the heat generated.

The higher the heat the shorter the trip time.

The heat generated from an overload condition causes the bi-metallic element to bend,tripping the breaker.

Short Circuit Condition - excessive current condition resulting from two or more phases making contact with one another.

Correlates to the second part of trip curve (I-Instantaneous )

During a short current flow can becomes thousands of times greater than the normal operating amperage.

A breaker short circuit current rating indicates the amperage value at which the breaker trips instantaneously.

Reaching current levels greater than the short circuit current rating will still result in an instantaneous trip.

The magnetic field generated from a short circuit attracts the trip mechanism to the element,tripping the breaker.

Maximum Interrupting rating- maximum current level the breaker can safely interrupt when properly applied within its rating.