RELETEK RS-MV36M Three Phase Voltage Monitoring Relay

The RELETEK RS-MV36M Three Phase Voltage Monitoring Relay is a compact protection device designed to monitor three-phase electrical supplies and protect motors, machinery, and industrial control systems against multiple voltage and phase-related faults. It combines overvoltage, undervoltage, phase failure, and phase sequence protection in a single DIN-rail-mounted relay.

The RS-MV36M can be configured for either three-phase three-wire or three-phase four-wire systems, making it suitable for different three-phase distribution arrangements. In three-wire mode, the relay supports nominal voltages of 380V, 400V, and 415V AC, with an operating range of 266V to 540V. In four-wire mode, it supports 220V, 230V, and 240V AC systems, with an operating range of 154V to 312V. The operating mode and nominal voltage are selected from the front panel.

The relay uses True RMS measurement and a microcontroller-based control system to monitor the incoming three-phase supply. True RMS measurement provides accurate effective-voltage measurement for AC monitoring applications. The RS-MV36M can detect when the supply voltage moves outside the configured limits and can also identify a missing phase or incorrect phase sequence. These functions are particularly important for three-phase motors because phase loss and reversed phase sequence can result in abnormal motor operation.

The voltage protection thresholds are adjustable. The overvoltage threshold can be set from 105% to 125% of the selected nominal voltage, while the undervoltage threshold can be set from 75% to 95%. Both overvoltage and undervoltage trip delays can be adjusted between 0.1 and 10 seconds, allowing the user to avoid unnecessary trips caused by short-duration voltage disturbances. The manufacturer specifies a fixed 2% hysteresis to help prevent rapid switching around the protection threshold.

For phase-related faults, the RS-MV36M provides phase-failure and phase-sequence protection. The specified trip time for incorrect phase sequence and phase failure is less than 0.5 seconds, providing fast response to these conditions. The model does not include adjustable voltage asymmetry protection; that function is provided by the RS-MV37M in the same product family.

The output is provided through 1NO + 1NC relay contacts, rated at 8A / 250V AC-1. The relay output can be used to control a contactor, which is the recommended approach when protecting higher-power motors, pumps, compressors, or other substantial loads rather than switching the load directly through the monitoring relay.

The RS-MV36M has a compact one-module DIN-rail housing and supports TH-35 rail mounting according to EN 60715. LED indicators provide visual indication of supply and output status, making the unit convenient for installation and troubleshooting inside electrical distribution boards and automation panels.

Features

• Three-phase voltage monitoring and protection

• Overvoltage and undervoltage protection

• Phase failure protection

• Phase sequence / reversal protection

• 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

• 1NO + 1NC relay output

• 8A / 250V AC-1 contact rating

• Compact 1-module DIN-rail housing

Specifications

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

Applications

• Three-phase motor protection

• Industrial automation panels

• Pump control systems

• Compressor protection

• Fan and ventilation systems

• Motor starter panels

• Three-phase machinery

• Electrical distribution boards

• Phase sequence monitoring

• Protection against abnormal supply voltage