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Why is the LCD display screen blank on a Micrologic Power or Harmonic type trip unit on a Powerpact P frame, R frame, or Masterpact circuit breaker?

FA228384

28 September 2021

Issue:
Why is the display blank on the trip unit?

Product Line:
Powerpact P frame, Powerpact R Frame, Masterpact NT, Masterpact NW

Environment:
Applied to Powerpact and Masterpact breakers with trip units with LCD displays.

Cause:
Need to power display of the trip unit without external power supply.

Resolution:
The LCD display on a Micrologic P or H trip unit will be blank unless the trip unit is energized.  Energization requires one of the following sets of conditions:
  1. The trip unit is energized by an external 24 Vdc applied to terminals F1-F2 (F1 negative-F2 positive)
  2. The trip unit is energized by an FFTK or HHTK test kit
  3. There is at least 100 V between two phases, AND the load reaches approximately 20% of the breaker's rated current.
  • Note that the display will not power up with primary injection testing unless one of the conditions in bullet 1 above is met.
  • Note that Ammeter trip units do not require external power and the display will come on with sufficient current flow alone.
See the following bulletins for more information on these trip units.
 
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