CLB Series Three-Phase Current Unbalance and Over Current Monitor

The CLB Series Three-Phase Current Unbalance and Over Current Monitor from the ATC Diversified Electronics division of Marsh Bellofram is used to protect three phase equipment against CURRENT UNBALANCE and OVER CURRENT conditions.

The control voltage is continuously applied to supply the sensing circuitry and the internal relay. When the current of any phase approximately 20% above the maximum operating current, the inrush delay begins. This delay disables the over current sensors while high inrush currents are present. Any time the currents are outside the preset limits
after completion of the inrush delay, the internal relay will de-energize (Drop-out).

A 2% differential (hysteresis) between Pick-up and Drop-out is incorporated to prevent chattering when operated in the automatic reset mode and the current is at the trip point. The reset mode is selected as follows:

  • AUTOMATIC: Place a jumper between pins ten (10) and eleven (11).
  • MANUAL: Place a normally open switch between pins ten (10) and eleven (11). When there is a loss and reapplication of the control voltage, the external switch must be closed before the circuit will again become operative.


  • OPERATING VOLTAGE: 3-Phase, 50/60 Hz, 600 V max
  • CONTROL VOLTAGE:  120 VAC, 50/60 Hz
  • OVER CURRENT:  See Table for Adjustable Ranges
  • UNBALANCE RANGE : 5% to 25%, Adjustable
  • INRUSH DELAY: 0.1 To 10 SEC, Adjustable; Initiated When Current of Any Phase rises 20% Above the Max. Operating Current
  • OUTPUT:  SPDT, 10 amp @ 240 VAC Resistive
  • HYSTERESIS: 2% of Unbalance Setting
  • RESPONSE TIME:  Operate 1 Second, Max. Release 100 mSEC
  • INDICATOR: LED Glow When All Conditions Are Normal
  • RESET: Automatic or Manual
  • TEMPERATURE RATING:  Operate 32° to 131°F (0° to +55°C); Storage:  -49° to 185°F (-45° to +85°C)
  • WEIGHT:   13 oz.