What is the difference between a short time and an instantaneous trip function?
Electrical Distribution Equipment
The short time pickup switch sets the value at which the breaker will trip after the set short time delay. This is shown as the center portion of the trip curve between long time and instantaneous trip.
The instantaneous pickup switch sets the trip value in multiples of ampere rating, at which the breaker will trip with no time delay. This is shown as the lower portion of the trip curve.