Electrical switching system for LV equipment with short circuit protection e.g. for contactors, protection relays and circuit breakers

摘要

The three lines L1,L2,L3 of a 3 phase ac supply have bimetallic safety switches Fi,F2,S1M coupled to a load M. The main switch S1M has a mechanically actuated stage Q that isolates the that load The resistance of the lines is measured P and is compared with a reference value. If the actual value falls below the threshold a signal generator H is operated and a solenoid Y responds to prevent a short circuit.