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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?

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 requires more power than the iron core CT's provide, and will be blank until one of the following sets of conditions is met:
  1. the trip unit is energized by an external 24 Vdc applied to terminals F1-F2 (F1 negative-F2 positive) or a FFTK or HHTK test kit
  2. unless 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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