To my knowledge, the PoE standard requires a Switch to be capable of detecting whether a connected device is PoE capable before delivering the full power via PoE. Why is there still often a warning, non-PoE Equipment might suffer damage if connected? This seems kind of contradictory to me?

2 Answers 2


There are some poorly designed or constructed devices. We experienced this with some devices that had pins shorted in a way that requested PoE from the switch, but the devices could not handle PoE, and they blew up when connected to a PoE switch interface. This was a design defect in the devices, and we needed to disable PoE on the switch interfaces where those devices were connected.


In addition to Ron's anwer, some PoE switches support proprietary, pre-standard PoE modes that weren't as thoroughly designed as 802.3af/at. When active, sending power to a device not supporting it gets more likely.

  • 2
    More to the point, some PoE sources provide a passive form of PoE, where instead of negotiating for power, power is always applied.
    – YLearn
    Feb 25, 2018 at 21:50

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