3 Phase Monitor Relays

3 Phase Monitoring Relays or Protective Relays, protect motors and equipment from expensive damage due to voltage faults on three-phase systems. Refer to the table below for more information on the level of protection offered by each product, then click one of the Series to see details about a specific product type.

Phase Reversal Phase Loss Undervoltage Overvoltage

Phase Unbalance


Plug-in Mounting
PCP Yes -- -- -- -- SPDT 10A
PLP Yes Yes -- -- -- SPDT 10A
PAP Yes Yes Adjustable
-- -- SPDT 10A
PJPU-FA8X Yes Yes No Yes

Indication Only


PMP Yes Yes Adjustable
Fixed at 110% Adjustable 2-10% SPDT 10A
PMP-FA8 Yes Yes Fixed at 90% Fixed at 110% Fixed at 6%


PMPU-FA8X Yes Yes Fixed at 90% Fixed at 110% Fixed at 6%


PMD Yes Yes Adjustable
Fixed at 110% Adjustable 2-10% DPDT 10A

Note: All products work on 50/60 Hz

* Provides isolated contact for alarm circuits | Learn more

3 Phase Monitoring Relay | Protective Relay


3 Phase Monitoring Relay | Protective Relay


3 Phase Monitoring Relay | Protective Relay



Depending on the unit selected, it will protect three-phase equipment against:

Phase Loss: total loss of one or more of the three phases. Also known as "single phasing." Typically caused by a blown fuse, broken wire, or worn contact. This condition would result in a motor drawing locked rotor current during start-up. In addition, a three phase motor will continue to run after losing a phase, resulting in possible motor burn-out.

Phase Reversal: reversing any two of the three phases will cause a three phase motor to run in the opposite direction. This may cause damage to driven machinery or injury to personnel. The condition usually occurs as a result of mistakes made during routine maintenance or when modifications are made to the circuit.

Phase Unbalance: unbalance of a three phase system occurs when single phase loads are connected such that one or two of the lines (phases) carry more or less of the load. This could cause motors to run at temperatures above published ratings.

Undervoltage: when voltage in all three lines of a three phase system drop simultaneously. This could result in an increase in current & motor heating and a reduction in motor performance.

Overvoltage: when voltage in all three lines of a three phase system increase simultaneously. Could cause a decrease in load current & poor power factor.


3 Phase Monitoring Relays | Protective Relays |Phase Monitor Relays
3 phase monitor video

3-phase monitor relay competitive comparison



Use this tool to build your catalog number by selecting features and options for a base product from this family.

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Macromatic's Three-Phase Monitor Relays Knowledge Base contains general and technical industry articles to help you learn more about Three-Phase Monitor Relays.

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