I have had this situation happen a few times where I found a device that was being supplied POE from an injector and that injector was plugged into a switch that is already providing POE. Obviously I remove the injector and it's done.

I have been having a problem with a users POE phone that has been having issues even after replacing the cables, phones and everything else. The phone would randomly stop working, or it would partially work and then it would work.

Anyways do POE injectors still work fine even though they may be plugged into a POE switch? Does the "double" power cause issues?

I just never heard of it causing issues so I am curious


The injector don't draw its power from the switch, it got its own power-supply, so the switch just operate in normal mode without PoE on the port. It's the injector that send the voltage to the remote gear.

This voltage is safe for users, but it can still damage equipment that has not been designed to receive POE. Therefore, before a POE switch or midspan (known as a PSE, for power sourcing equipment) can enable power to a connected IP camera or other equipment (known as a PD, for powered device), it must perform a signature detection process.

Signature detection uses a lower voltage to detect a characteristic signature of IEEE-compatible PDs (a 25kOhm resistance). Once this signature has been detected, the PSE knows that higher voltages can be safely applied.

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