RELETEK RS-MV34M Three Phase Voltage Monitoring Relay

The RELETEK RS-MV34M Three Phase Voltage Monitoring Relay is a compact voltage protection device designed to continuously monitor a three-phase electrical supply and disconnect the control circuit when the monitored voltage rises above or falls below the preset limits. It is intended for protecting motors, machinery, control panels, and other three-phase electrical equipment from abnormal supply-voltage conditions.

The RS-MV34M provides adjustable overvoltage and undervoltage thresholds, allowing the protection limits to be matched to the nominal three-phase supply. The overvoltage threshold can be adjusted between 105% and 125% of the selected nominal voltage, while the undervoltage threshold can be adjusted between 75% and 95% of the nominal voltage. This allows the relay to respond to voltage deviations according to the requirements of the connected equipment.

The relay can be configured for either three-phase three-wire or three-phase four-wire systems. For three-wire systems, the selectable nominal voltages are 380V, 400V, and 415V, with an operating range of 266V to 540V. For four-wire systems, the selectable nominal voltages are 220V, 230V, and 240V, with an operating range of 154V to 312V. The operating mode and nominal voltage are selected from the front panel.

The RS-MV34M uses True RMS measurement and a microcontroller-based control system. True RMS measurement provides a more representative measurement of AC voltage for monitoring applications compared with simple average-responding measurement methods. The device also includes a configurable trip delay from 0.1 to 10 seconds, allowing temporary voltage fluctuations to be ignored rather than causing an immediate relay trip.

A fixed 2% hysteresis is provided to help prevent rapid relay switching when the measured voltage is close to the selected protection threshold. The manufacturer specifies a delay error of ±10% + 0.1s and a knob-setting error of 1% of the scale value.

The RS-MV34M provides 1NO + 1NC relay contacts with an 8A / 250V AC-1 rating. The output is intended primarily as a control signal and can be connected to a suitably rated contactor when protecting higher-power motors or other substantial electrical loads.

The unit has a compact one-module DIN-rail housing and is designed for TH-35 rail mounting according to EN 60715. LED indicators provide visual information about the supply and output state, making the relay suitable for installation inside electrical distribution boards and automation control panels.

Important: The RS-MV34M is specifically an under/overvoltage monitoring relay. In the same RELETEK family, models such as the RS-MV36M add phase-failure and phase-reversal monitoring.

Features

• Three-phase overvoltage and undervoltage monitoring

• True RMS voltage measurement

• Microcontroller-based operation

• Selectable 3-phase 3-wire or 4-wire operation

• Adjustable overvoltage threshold: 105–125% of Un

• Adjustable undervoltage threshold: 75–95% of Un

• Adjustable trip delay: 0.1–10 seconds

• Fixed 2% hysteresis

• 1NO + 1NC relay output

• 8A / 250V AC-1 contact rating

• LED indication for supply and output status

• Compact 1-module DIN-rail housing

Specifications

Specifications are based primarily on RELETEK's official RS-MV31M–37M technical documentation.

Applications

• Three-phase motor protection

• Industrial automation panels

• Electrical distribution boards

• Pump control systems

• Compressor protection

• Fan and ventilation systems

• Three-phase machinery

• Motor starter panels

• Control-panel voltage monitoring

• Protection against abnormal supply voltage