Model# 272

Current Unbalance Detector

The Model 272 3-Phase Current Unbalance Detector monitors 3-phase lines to detect an unbalanced current. It can also monitor three separate single phase lines for equal current levels. The percentage of unbalance is adjustable from 2% to 25% by adjusting a front panel control. An unbalance greater than this setting energizes the relay. An adjustable trip delay of 0.5 to 10 seconds is provided. For optimum performance, operating currents should be kept in the 1 to 5 amps range. However, zero current on each phase is considered to be a balanced condition. Continuous currents, up to 10 amps per phase, will not damage the unit, nor will current surges up to 40 amps for 2 seconds. The contacts are automatically reset when the unbalanced condition is corrected. A supply voltage of 24 or 120 VAC is required for this unit.

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Input Votlage:
– 24Vac
– 115Vac
Input Range:
– 20-28Vac
– 100-130Vac
Power Consumption: 1.5W
VA Burden: 0.5VA per phase
Frequency Range: 50-400Hz
Current Range: 1-5Aac
Maximum Input Current: 40 amps for 2 seconds
Unbalance Adjustment: 2% – 25%
Trip Delay: 0.5 to 10 seconds +/- 20%
Contact Rating: SPDT 10A at 240Vac resistive
Expected Relay Life:
– Mech: 10 million operations
– Elec: 100,000 at rated load
Transient Protection: 2500V for 10msec
Operating Temperature: -40° to +131°F
Humidity Tolerance: 0-97% w/o condensation
Enclosure Material ABS plastic
Weight 1.5lbs



  • Mount the Model 272 in a suitable enclosure.
  • Connect AC operating power to the appropriate terminals.
  • Connect the normally closed (N.C.) relay contacts to the load control wiring.
  • Connect the 3-phase currents or CT outputs to the current input terminals marked A B C.
  • Set the PERCENT UNBALANCE and TRIP DELAY adjustments to the desired levels, and apply operating power.


Should the monitor fail to operate properly, check that all three currents are present and are of the correct level. Check all fuses and verify that all wiring connections are correct. Should problems persist, contact the factory at for assistance.

  • Adjustable trip delay
  • Adjustable unbalance percentage
  • Automatic Reset
  • CSA

  • RU