Undervoltage Settings on Universal Voltage Three Phase Monitor Relays

Posted: 4/14/14 | Three-Phase Monitor Relays


Your new PMPU three-phase monitor relay can work on any voltage between 190 & 500V. It also includes an adjustable under-voltage trip setting of 80-95% and a fixed overvoltage trip setting of 110%. How do these percentages work depending on where you set the line-line voltage?


On the PMPU products, one of the first settings to make is the line-line voltage. Although the products will work on any voltage from 190-500V, the user must first set the line-line voltage based on their actual system voltage.

Once the line-line voltage is set, the product then uses that value as the basis for determining the under-voltage and overvoltage trip settings.  The under-voltage trip setting will always be calculated from 80-95% of the line-line voltage setting and the overvoltage setting will always be 110% of the same setting. 

For example, if you set the line-line voltage setting at 230V and the under-voltage setting at 90%, the unit will trip once the voltage decreases to a value of 207V or less (90% * 230) for a period longer than the trip delay setting. With the same nominal voltage setting of 230V, the unit will trip once the voltage increases to a level of 253V or higher (110% * 230) for a period longer than the trip delay setting.

The same discussion applies to the PMDU surface-mount products, except these products have a line-line voltage range of 208-480V.

For more information on how to set up these three-phase monitor relays, click the appropriate series to view the instruction sheet for each one ( PMDU/PMPU).

If you need additional assistance, please contact Macromatic.