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Pinout of PoE (Power over Ethernet) Cables#

This article provides the pinout of the GigE cables compliant with the PoE (802.3af) standard.

Gigabit Ethernet requires the use of eight wires. However, it is possible to use only four wires if you don't need the whole bandwidth.

The following table is taken from Wikipedia:

Pinout of GigE Cables

Here is an explanation of the four rightmost columns:

  • 10/100 mode B, DC on spares:
    • Power is supplied on four dedicated pins
    • Data is supplied on four different pins
  • 10/100 mode A, mixed DX & data:
    • Using phantom power, you can save four wires and run at 10/100. This can be useful if you don't need the Gigabit speed and want to simplify cabling.
  • The two 1000 (1 gigabit) columns correspond to high speed with PoE. All the eight wires are used, using phantom power again.

Phantom power technique allows power supply and data transfer on the same physical medium.

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