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What does it mean when all of the LEDs on the left of my AP77XX Rack Automatic Transfer Switch (ATS) front panel are illuminated?


All of the LED indicators on the front left of my Rack ATS are illuminated. See below for the specific LEDs.

A different, non standard LED combination with an audible click every 2 to 3 seconds may be observed and/or the front display may also read Er.

Product Line

  • Rack Automatic Transfer Switches (specific models only)
    • AP7721
    • AP7722A
    • AP7723
    • AP7724
    • AP7730
    • AP7731
    • AP7732
    • AP7750A
    • AP7752
    • AP7752J
    • AP7753


  • All serial numbers
  • All firmware versions


This is due to an internal communication failure between the device (the ATS) and the embedded Network Management Card typically.


This needs to be verified by connecting to the ATS via the embedded Network Management Card (instructions outlined in knowledge base ) to verify that the on board event log says Automatic Transfer Switch : Lost communication with the ATS or Communication has been lost to the device! or similar.
If this is validated along with the LED condition, it is likely the ATS must be replaced due to the communication failure.

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