As I understand IEEE PoE standards, the PSE detects PoE capability of the connected device (PD) by measuring resistance on certain pairs and then negotiates its PoE requirements.


  1. Do passive PoE PSE perform the measurement before outputting power?
  2. Is there any PoE injector or midspan PSE that does so?
  3. Is there a risk of damaging equipment when connecting a non-PoE device down the line of passive PoE injector? Do Ethernet controllers include any protection against such damage? (thinking laptop, basic switch...)

The definition of "passive" PoE is that the power supply doesn't try to negotiate or determine anything. That is what differentiates it from "active" - i.e. standard - PoE.

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