Thermal Trip Unit(region one)
The first slopping region of the circuit breaker curve is a graphical representation of the tripping characteristics of the thermal trip unit, the trip unit bends to trip circuit breaker trip bar in conjunction with a rise in amperage over time.
Magnetic Trip Unit(region two)
This region of circuit breaker curve is the instantaneous trip unit, which interrupts a short circuit in 2.3 to 2.5 miliseconds.Because of this, the curve has no slope and it graphically represented as a vertical straight line.
Breaker Contacts(region three)
This region of the curve is the time required for the contacts of the circuit breaker to begin separate, the contacts will open in less than 0.5 miliseconds and is graphically represented by the bottom vertical portion of the curve.