Monitor
The sensing network continuously compares the incoming phases of the three-phase voltage.
Three-phase motor protection
Protect equipment before a power fault becomes downtime.
Phase-Guard continuously monitors phase-voltage balance and works with magnetic controls to stop motors and other equipment from operating under damaging phase conditions.
UL listed modelsMade in the USAProtecting equipment since 1936
Phase lossDetects open-phase and single-phase conditions
Voltage unbalanceResponds when phases move outside safe balance
Sequence & voltageOptional reverse phase, low, and high voltage protection
How it works
Continuous monitoring. Automatic response.
Phase-Guard is a self-contained power-sensing device—not a thermal device. It responds directly to abnormal conditions in the three-phase supply.
Detect
When a phase becomes more than 12% unbalanced or phase loss occurs, the unit recognizes the fault.
Protect
The master output relay trips after an approximately 1½-second delay, helping prevent nuisance trips.
Protection thresholds and timing can be tailored using the Phase-Guard Admin Software.
Choose your relay behavior
Two models, one flexible platform
Select the standard operating behavior for your control circuit. Add the Normal Relay Selector option to switch modes later through software.
Model P
Energized during normal conditions
The output relay is energized while monitored power conditions are normal.
View Model P details →Model PND
De-energized during normal conditions
The output relay remains de-energized while monitored power conditions are normal.
View Model PND details →Customize for the application
Use Admin Software to adjust device settings and match your specific operating environment.
Explore Admin Software →Add features in the field
License additional capabilities after installation, without replacing or shipping the device back.
See the upgrade process →Deploy when needed
Keep units ready in inventory, then configure or upgrade them for the application before deployment.
Browse available options →Applications
Built for magnetically controlled three-phase equipment
Phase-Guard monitors a three-phase supply line and works with controls including push-button stations, thermostats, pressure switches, and float switches. It can also support manually operated starters with shunt or capacitive trip devices.
- Individual three-phase motors
- Unattended motors and ventilation fans
- Pumps, refrigeration, and air conditioning equipment
- Welders, computers, or groups of motors on a common contactor
Flexible by design
One platform for a wide range of systems
Broad voltage support
Standard models are available for 120, 208, 240, 480, 550, and 600 VAC operation.
Any horsepower rating
Protect motors of any horsepower rating at the selected operating voltage.
Individual or group protection
Protect one motor or multiple motors fed from a common contactor or magnetically latched circuit breaker.
Automatic recovery
After a phase fault clears and normal conditions return, Phase-Guard automatically resets unless configured otherwise.
Simple installation
View Wiring Diagram
Connect, control, and protect.
Connect three-phase power at L1, L2, and L3. DPDT master-relay contacts rated 30 amps at 277 VAC can open or close the customer’s protection circuit.