Undervoltage Settings on Universal Voltage Three Phase Monitor Relays

Three-Phase Monitor Relays


Your new PMPU three-phase monitor relay can work on any voltage between 190 & 500V. It also includes an adjustable undervoltage 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 undervoltage and overvoltage trip settings. The undervoltage 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 undervoltage 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 tech support at 800-238-7474.