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APC (American Power Company) PDU wiring Scheme

Applies to devices such as the AP7920 from These are rack mount networked power distribution units which allow for the current to its power sockets to be controlled/monitored and exposed through a web and SNMP interface.

An RJ12 serial connector is used as a last resort/firmware-reset/password recovery option. And also allows for some (but not all, see note) functions to be controlled over this serial connection (e.g. in conjunction with a analog/gsm modem).

Connector on the device itself:

6 pin RJ12 (6P6C) female connector layout 6 pin RJ12 (6P6C) female connector on the front of the PDU

Connector on the server



APC/PDU name RJ12 pin Direction DB9 Pin Serial Name Description
na 1 na 1 na Unknown
GND 2 5 GND Ground (using either is fine)
RX 3 2 RX Server to PDU comms 9600, 8N1
TX 4 3 RX PDU to Server comms 9600, 8N1
GND 5 5 GND Ground (using either is fine)
na 6 na na Unknown


Using either ground is fine; nor do they need to be interconnected. The recent procedure is:

  1. Ensure the unit is powered up and ‘clicked on’ - can take some 100 seconds.
  2. Connect rj12/DB9 connector and ensure terminal is in 9600, 8N1
  3. press the reset button and let go
  4. await for the orange LED to start flashing
  5. press the reset button again before it stops flashing.
  6. the serial port will now be at 9600 8N1, username/password ‘apc’, ‘apc’ for 30 seconds.
  7. wait about 2-3 seconds for the LED to change (or repeatedly press return on the terminal).
  8. press return to get the ‘Username’ prompt.

Note that some APC units have a watchdog and re-initielize ever 7 to 9 minutes if they cannot ping their gateway and/or see any traffic on their ethernet wire.

Furthermore note that due to a crypto-click-through licenses some crucial security configuration steps can only be completed through the Web UI; and not over the serial port or ssh connection (as of HW/software/Network versions B2/265/264, late 2005, early 2006).


Documentation on the APC: 1.

Category:Serial Cables


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