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AP8XXX Rack PDU 2G "NMC CAN Bus Off" Error


My AP8XXX series Rack PDU 2G product is displaying a "CAN Bus Off" error within the interface or event log. See below:

Event Log: Rack PDU ##: NMC CAN bus off.

Web UI v5.1.X:

Web UI v6.X.X:

Product Line

  • Rack Power Distribution
    • All AP8XXX Rack PDU 2G models


  • All firmware versions (unless otherwise noted)
  • All serial numbers


The CAN bus on the Rack PDU products is represented to the user via In and Out Ports, noted in the below image.

These ports are for use with the Network Port Sharing feature available in rpdu2g v5.1.6 and higher. For units manufactured later than December, 2012, you may find a CAN bus terminator pre-installed in one of these ports.

NMC CAN Bus Off is an error message that can present itself when unsupported items are connected to the aforementioned IN or OUT ports. These ports are RJ-45 connectors so items such as an Ethernet cable or environmental monitoring probe/accessory could be mistakenly connected to the CAN bus which will disrupt communication. If the source of the disruption is removed and no internal damage has occurred, the "NMC CAN Bus Off" error should clear on its own.


As noted in the release notes for v5.1.6 rpdu2g firmware, this message may not clear itself due to the following firmware issue:

After a "CAN bus off" alarm has been resolved, the clearing event is not generated and the alarm remains in the active list.

A reboot of the management interface should clear this error. If it does not, refer to the steps below.

  • Visually verify that everything is removed from the IN and OUT ports shown above. For AP8XX and AP89XX SKUs, this includes any RJ-45 terminators provided by APC or Schneider Electric for troubleshooting. Newer lower profile terminators are very tiny so please inspect carefully. AP84XX and AP86XX SKUs require the RJ-45 terminator to function properly as noted in knowledge base FA156187. If you're using Network Port Sharing, communication will be lost temporarily between the PDUs in your group.
  • Reboot the management interface of the Network Management Card via CLI or web UI. Observe if error message has cleared.
  • Replace any terminators. Verify error does not return.

If you're using Network Port Sharing, instructions on installing terminators are outlined in the user's guide or in knowledge base article FA164436 under Installation Instructions.

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