SLE Series Phase Monitor

The SLE Series Phase Monitor from the ATC Diversified Electronics division of Marsh Bellofram Corporation is designed to protect three-phase equipment against Phase Unbalance, Phase Loss, and Under Voltage.
With normal operating voltage present on all three phases, the internal relay will energize (PICK-UP). When a phase loss occurs or the voltages fall outside the preset unbalance or under voltage settings, the internal relay will de-energize (DROP-OUT). The relay automatically resets when the line conditions return to normal. Both Delta and Wye systems may be monitored. In Wye Systems, connections to neutral are not required.

NOTE: When a phase is lost while the motor is running, a condition known as regeneration occurs where a voltage is induced into the open phase nearly equal in magnitude to the normal phase-to-phase voltage. The SLE series is designed to detect this condition when properly adjusted.



  • Models available up to 480 VAC
  • Protects 3-Phase Equipment Against:
    • Phase Loss
    • Under Voltage
    • Phase Unbalance
  • Lock Shaft Adjustment for:
  • Phase Unbalanced Percent
    • Under Voltage Drop Out
    • Automatic Reset
  • Delta or Wye Systems