On a sunny day (Sun, 29 Jul 2018 22:51:34 +0300) it happened Tauno Voipio
 wrote in :

>On 29.7.18 21:40, Dave Liquorice wrote:
>> On Sun, 29 Jul 2018 16:36:48 +0100, Richard Ashbery wrote:
>>
>>> I would be a little concerned about loading my ethernet cable with say a
>>> Raspberry Pi but I guess some of you are finding it works OK.
>>
>> With proper PoE the full 48 V is not present on the cable until the
>> sending end has had a chat with the far end to see if it wants power.
>> It's perfectly safe to plug anything onto a proper PoE supplied
>> cable.
>>
>> This is not the case with passive PoE, where the full power is
>> present all the time.
>
>
>In PoE, the feed is between the transmit and receive pair centerpoints.
>
>A proper Ethernet interface has transformers on both pairs, so supply
>feed in a normal network card is not an issue.

Be carefull, there will be resistors between those points.

Putting 48V on such an ethernet connector will smoke those resistors.

IIRC the logic in the POE supply tests for this.

You will need to replace connectors for special ones without
those resistors if you just want to put a voltage on the cable,
when not using an 'intelligent' controller.

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