cnMatrix TX Switches
Device connectivity issue
Document Number FSB9086
Revision v001
Download the PDF version Application Global
Effective Date February 1, 2023
Expiry Date N/A
  Warranty Service   High – Perform immediately
  Informational   Medium – Perform at next scheduled maintenance
  Customer Specific X Low – Perform when system exhibits symptoms

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Subject: cnMatrix TX switches susceptible to unexpected behavior when devices that require low voltage passive PoE are connected.

Software/Configuration AFFECTED: cnMatrix TX 2K and TX 1K switches

Sympton: This applies to cnMatrix TX switch access ports that are connected to devices that use low voltage (24V) passive PoE. In some cases, the following symptoms can be seen.

  1. Devices may not power up or can lose connectivity and
  2. When disabling the PoE to the affected devices, the management interface will indicate that power is disabled, however the device will remain powered on.
  3. Reported power draw is inaccurate.
This problem is only applicable to the cnMatrix TX switches.
This is not a problem with devices that use standards based active PoE. This is also not a problem with devices that use
48V/54V passive PoE.
Only devices that use low voltage (24V/30V) passive PoE can potentially have this problem. This is dependent on the grounding solution that the device uses. If the device isolates the PoE ground, then there will not be a problem. The problem only occurs if the device does not properly isolate its PoE ground.
The root cause and resolution for this problem is well understood. If this problem exists, the solution is to use an external dongle that isolates the improperly grounded device from cnMatrix. This dongle is available today from 3rd party sources. Please discuss with Your Cambium support team for guidance on a solution.
If you have questions or concerns, please contact Cambium Technical Support at the following:

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