CMU Series AC Under Current Monitor

The CMU Series AC Under Current Monitor from the ATC Diversified Electronics division of Marsh Bellofram is an AC under current monitoring relay with adjustable time delay, designed to prevent damage and premature equipment failure in pumps, motors and other critical machinery and equipment. The internal relay is energized (pick-up) when monitored AC current is above the preset trip point. The relay de-energizes (drop-out) when the current falls below the trip point for longer than the adjustable delay. The delay is incorporated to prevent nuisance tripping caused by momentary line dips. The relay, which includes an automatic reset feature, re-energizes when the current rises 5% above the drop-out trip point for longer than 0.1 seconds.  An external CT may be used to extend the range of the current monitor.



  • AC under current monitoring relay
  • Energized relay in normal current conditions
  • Models available from 0.05 to 10 amps
  • Plug-in or surface mount enclosure
  • Adjustments for:
    • Current trip point
    • Release time
  • Automatic reset


  • Current demand level monitoring
  • Conveyor or motor load jam detection
  • Dull bit or blade detection
  • Remote motor sensing
  • Broken fan belt or chains detection
  • Feed rate to keep two loads at their most efficient point