IEEE 1458:2005 pdf free download – IEEE Recommended Practice for the  Selection, Field Testing, and Life Expectancy of Molded Case Circuit Breakers for Industrial Applications
3.5.2 Over-toggle
In a circuit breaker with an over-toggle mechanism, a manual handle on the circuit breaker is operated to setthe mechanism in motion. The handle is moved to open or close the circuit breaker until a point is reachedwhere the handle goes over-toggle (past the point of no return), and the spring-assisted mechanism automat-ically opens or closes the circuit breaker.This toggle mechanism is called the quick-make, quick-break type,meaning that the speed with which the contacts open or close is independent of how fast the handle ismoved. A motor operator can be used to operate the handle automatically in licu of manually going throughthe motion. The design is such that the circuit breaker would trip open when called upon to provide itsexpected protection, even if the manual handle were to be held in the ON (closed) position.
Storing the energy in the springs is accomplished through the use of a manual-charging handle, an automaticmeans through the use of a small electric motor, or both. By having the ability to re-charge the closingsprings, the circuit breaker can rapidly and remotely reclose after a fault. This ability to attempt a reclosureif a fault causes the circuit breaker to trip is designed to provide the user with a high degree of service conti-nuity.Closing the circuit breaker can be accomplished by using a manual pushbutton or an electrical closingsolenoid.
3.5.4 Electromagnetic assistance
Many molded case circuit brcaker designs achieve high interrupting ratings by being designed to take fulladvantage of certain natural facts of physics to assist the operating mechanism with the opening process.This concept centers on a natural repulsion between two parallel conductors with current running in them inopposite directions.
While on the subject of the importance of the application of electromagnetic theory to circuit breaker design,it is appropriate to note that some new low-voltage power breaker designs take advantage of electromagneticforces in both directions, opening and closing. Designs are such that the forces are used to help hold the con-tacts closed against a fault when required, and then reversed to assist with the opening process.
3.6 Means to extinguish an arc
An arc is defined as a discharge of electric current crossing a gap between two contacts. Arcs are formedwhen the contacts of a circuit breaker are opened under load. Arcs can be very destructive and vary greatlyin size and intensity. The size of the arc depends on the amount of current present when the contacts arepulled apart. For example, the arc formed when a normal load current is broken would be insignificant incomparison to the arc formed when a short-circuit current is broken. Since arcs cannot be prevented, circuitbreakers are designed to control them.
The heat associated with an arc creates an ionized gas environment.The bigger the arc, the more heat cre-ated. The more heat created,the more ionization that takes place. The more ionization,the better theconditions are for an arc to be maintained and grow.Obviously, this is the condition that must be dealt withquickly and effectively by a circuit breaker. The important thing to remember here is that the ability of thecircuit breaker to control the arc is the key to its short-circuit interrupting capability. Of all overcurrent con-ditions, the short circuit is potentially the most devastating.
3.6.1 Current zero and arc extinguishing
When considering alternating current, it is important to note that there is no current flowing at each pointzero (current zero) in the cycle. This is a very important aspect of arc extinguishing. With no current at pointzero,conditions are optimal for preventing an arc from continuing.