They are an ammeter for measuring the current in each phase of a 50-60 Hz three-phase line. Three-phase voltmeters are used for measuring the voltages between phases, or phase-phase and phase-neutral in a line. They incorporate a switch in order to select the wires between which the measurement is desired.
The EQ..n SWT also has a position of disconnection in the switch (OFF). They indicate the rms value of the voltage, even with high harmonics, with a minor influence on the accuracy.