Abstract: A microprocessor based overcurrent trip unit includes an analog circuit for monitoring phase currents in the electrical interrupting device. The analog circuit is adapted to interface with the microprocessor over a range of selectable setpoints for instantaneous tripping and at the same time accurately monitor the phase currents even during a condition when the current sensing transformers are saturated. The overcurrent trip unit also allows the function of the long time delay characteristics of protection curve to be varied in order to provide better coordination with the characteristics of other overcurrent tripping devices in an electrical distribution system, such as a current limiting fuse, thereby enhancing the overall reliability of the system. For example, the function may be varied to provide either a fixed or FLAT, It, I.sup.2 t and I.sup.4 t functions.

Abstract: A mechanism-operated cell switch (MOC) is provided for metal-clad switchgear. The cell switch actuates an auxiliary set of contacts for the main circuit interrupter. The main circuit interrupter may be disposed in two positions within the metal enclosed switchgear. In the first position it is connected to the high voltage terminals of the cell for external circuit protection. In the second position it is not connected to the high voltage terminals but nevertheless remains in the cell for test purposes. In either position the mechanism operated cell switch may be actuated in conjunction with the actuation of the main circuit interrupter. However, in the second or test position the mechanism operated cell switch may be bypassed if desired.