SLC Series Phase Unbalance and Loss Monitor

The SLC Series Phase Unbalance and Loss Monitor from the ATC Diversified Electronics division of Marsh Bellofram Corporation is designed to protect 3-phase equipment against Phase Unbalance and Phase Loss conditions.
With normal operating voltages applied to all three phases, the internal relay will remain de-energized (DROPPED-OUT).
When a Phase Loss or Phase Unbalance exceeding the pre-selected trip point occurs, the relay will energize (PICK-UP). The SLC series is typically used in conjunction with a shunt trip breaker.

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 SLC 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 Reversal
  • Delta or Wye Systems
  • Adjustable Phase Unbalance Percentage
  • Automatic Reset
  • Several Enclosure Styles