Phase Monitor Relays from Macromatic

Phase Monitor Relays are sometimes called 3 Phase Monitors, Three Phase Monitor Relays, Phase Loss Relays, Single Phase Relays, Phase Sequence Relays, Protective Relays, Motor Protection Relays or Phase Failure Relays.  They provide motor protection against premature equipment failure caused by voltage faults on 3 Phase systems. These devices are designed to be compatible with most Wye or Delta systems. In Wye systems, a connection to a neutral is not required. Phase Monitor Relays protect against unbalanced voltages or single phasing regardless of any regenerative voltages.

Refer to the table below for more information, then click one of the Series to see details about a specific product type. If you have any questions regarding the selection or application of phase monitor relays, either visit our on-line Technical Resource Center or call us at 800-238-7474.

PCP Series Plug-in Phase Monitor Relays PAP Series Plug-in Phase Monitor Relays PMD Series Surface-Mount Phase Monitor Relays
PCP2 PAP480 PMDU

(Click on Series to View Product Specifications)
Series Offers Protection Against: Nominal Voltages Mounting Output Configuration
Phase Reversal
(Phase Sequence)
Phase Loss
(Single Phase)
Undervoltage Overvoltage Phase Unbalance
PCP Series Yes -- -- -- -- 208-480V (one version),
separate 120V version
Plug-in SPDT
PLP Series Yes Yes -- -- -- 120V, 208V, 240V, 400V & 480V Plug-in SPDT
PAP Series Yes Yes Adjustable 75-95% of Nominal -- -- 120V, 208V, 240V, 400V & 480V Plug-in SPDT
PMP Series Yes Yes Adjustable 80-95% of Nominal Fixed at 110% of Nominal Adjustable 2-10% 208-480V (one version),
separate 120V version
8 Pin Plug-in SPDT
PMP-FA Series Yes Yes Fixed at 90% of Nominal Fixed at 110% of Nominal Fixed at 6% 208-480V (one version),
separate 208V & 240V versions
8, 11 & 12 Pin Plug-in SPDT, DPDT & SPDT/SPNO
PMD Series Yes Yes Adjustable 80-95% of Nominal Fixed at 110% of Nominal Adjustable 2-10% 208-480V (one version), separate 120V & 575V versions Surface SPDT/SPNC

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. The unit trips if rotation (sequence) of the three phases is anything other than A-B-C.

Phase Loss: A 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. A Macromatic phase monitor relay trips on the loss of any Phase A, B or C.

Undervoltage: When voltage in all three lines of a three phase system drop simultaneously. On our units, it is adjustable as a percentage of nominal voltage. Unit trips when the average of all three lines is less than the adjusted set point for a period longer than the adjustable time delay drop-out.

Overvoltage: When voltage in all three lines of a three phase system increase simultaneously. Overvoltage protection is fixed at 110% of nominal voltage on PMP & PMD products. Unit trips when the average of all three lines is greater than the fixed set point for a period longer than the time delay drop-out.

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. The PMP & PMD Series products are adjustable from 2 - 10% unbalance. Unit trips when any one of the three lines deviates from the average of all three lines by more than the adjusted set point . There is also a "Disable" setting adjustment that will turn off the Phase Unbalance Protection if nuisance tripping is a problem.

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