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Video: Automatic Transfer Switch (AP44XX) front panel LEDs explained

This FAQ document explains the behavior of the LEDs located on the front panel of the fourth generation rack automatic transfer switches (ATS).

Product Line:
4th Generation Rack Automatic Transfer Switch models: AP4421, AP4422, AP4423, AP4424, AP4430, AP4431, AP4432, AP4433, AP4434, AP4450, AP4452, AP4452J, AP4453.

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Request to explain the behavior of the LEDs and functionality of the Preference button located on the front side of the ATS.

Refer to Picture 1 and Table 1 for a detailed description on the LEDs and Preference button located on the front panel of the ATS unit.
ATS front display
Picture 1
(1) Preference A/B ButtonPress to set a preferred source: the first press sets source A, the second press sets source B, and the third press sets no preference. Flashing preference LED's mean the input sources are out-of-phase with each other, which can extend the total transfer time.
(2)Source A and B LEDsIndicate preferred source. If no source is preferred, both LEDs are illuminated. You can also see the preferred source on the LCD Display.
(3)Input Connector LEDsProvide information about input voltage from each source. If the RMS input voltage and measured frequency are within the selected tolerance range, the corresponding indicator will be illuminated. In a normal operating condition (full source redundancy) both sets of LEDs are illuminated.
(4)Output Connector LEDsIndicate which source is being used for the output (only one path will be illuminated at any time). Together, the Source Preference LEDs, the Connector LEDs, and the Output LED show the power flow through the ATS.
(5)Output LEDShows that voltage is available at the output for the ATS.
Table 1

The video embedded below shows the front panel LED behavior as explained above and demonstrates the switching between the input sources by using the Preference A/B Button (in the first half of the video), ATS switching functionality in case of a failed input source (01:04) and preferred source switching functionality (01:17).
For more information about the ATS switching functionality please see FAQ FA327612.

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