The multi-functional VMD420 series voltage relay is designed to monitor the frequency, undervoltage and overvoltage and the voltage between two threshold values in 3(N)AC systems. The voltages are measured as r.m.s. values. The currently measured value is continuously shown on the LC display. The measured value required to trigger the alarm relay is stored. Due to adjustable response times, installation-specific characteristics, such as device-specific start-up procedures, short-time voltage fluctuations, etc. can be considered. The devices require an external supply voltage.

• Monitoring of voltage-sensitive machines and electrical installations
• Switching machinery and equipment on and off at a certain voltage level
• Monitoring of stand-by and emergency supply systems
• Supply voltage monitoring of portable loads
• Protection of three-phase motors against phase failure and phase open-circuit
• Transformer protection, asymmetrical load can be recognised

• Undervoltage, overvoltage and frequency monitoring in 3(N)AC systems 0…500 V
• Asymmetry, phase failure and phase sequence monitoring
• Various monitoring functions selectable
< U, > U, < f, > f
• Start-up delay, response delay and delay on release
• Adjustable switching hysteresis
• r.m.s. value measurement (AC+DC)
• Digital measured value display via multi-functional LC display
• Preset function
(automatic setting of basic parameters)
• LEDs: Power On, Alarm 1, Alarm 2
• Measured value memory for operating value
• Continuous self monitoring
• Internal test/reset button
• Two separate alarm relays
(one changeover contact each)
• N/C or N/O operation and fault memory behaviour selectable
• Password protection for device setting
• Sealable transparent cover
• Two-module enclosure (36 mm)
• Push-wire terminal
(two terminals per connection)
• RoHS compliant