Ammeter selector switch is basically a normal three position switch. In large Electrical distribution panels an ammeter is used to monitor the current through each line. The basic idea behind the use of ammeter selector switch is to reduce
the number of ammeters used to monitor line currents. Otherwise in a three phase system in order to monitor current in each line separate, ammeters have to be used in each line. In order to avoid that an ammeter selector switch is used to select the line in which the current is to be monitored.