The ITH is a solenoid operated device with an adjustable core screw which adjusts the ac current pickup of the device over a 2 or to 1 range.
Operating speed of the ITH unit over nominal range (60 Hz base) is as follows:
at 200% of trip setting - less than 1 cycle
at 500% of trip setting - 1/2 cycle
at 1000% of trip setting - 1/4 cycle