Issue:
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.


Environment

• All firmware revisions
• All serial numbers

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


Resolution:
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.

Picture 1

Item		Function
(1)	Preference A/B Button	Press 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 LEDs	Indicate 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 LEDs	Provide 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 LEDs	Indicate 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 LED	Shows 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.

Released for: Schneider Electric Egypt and North East Africa