Voltage monitors or indicator:

• Digital timing, counting, control, and monitoring devices with a 48 x 96 mm panel mounting design are available in a compact housing design.
• provide many innovative features, including multiple relay output choices and a re-transmit (re-tx) function that provides an extra 4–20 mA output when used with certain monitoring devices.
• Shows the actual RMS single- or three-phase supply voltages and/or keeps track of them.