The Power over Ethernet (PoE) cable power supply allows a voltage of 48 V, up to 13 watts of electrical power, in addition to 100 Mbit/s or 1 Gbit/s data. This technology is defined by the IEEE 802.3af standard, part of the IEEE 802.3 (Ethernet) standard ratified on 11 June 2003 and published on 11 July 2003.

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An Ethernet cable consists of four pairs of wires. When the connection is established at 100 Mbit/s, data is transmitted over only two pairs, namely wires 1, 2, 3 and 6. The other two unused pairs, namely wires 4, 5, 7 and 8, can be used to carry electrical current. PoE can "pass" through the wires of the data pairs, this mode of operation is then called "end-point" or through the wires of the unused pairs in 100 Mbit/s in "mid-span" mode.

 

When the connection is established at 1 Gbit/s, all four wire pairs are used for data.

 

This technology has evolved to provide more power and is called PoE+.

 

• PoE vs PoE+ :

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IEEE 802.3af (PoE): The power supply provided by the equipment (switch, injector) is a maximum of 15.4 W for a maximum power of 12.9 W at the device. The nominal voltage is 48V, and can vary from 44V to 57V in transmission.

 

IEEE 802.3at (PoE+): If both the equipment providing the power and the device meet this standard, then a maximum power of 25.5 W at the device can be used for a maximum emission of 30 W, always for a nominal voltage of 48V.

 

An Ethernet cable consists of four pairs of wires. When the connection is established at 100 Mbit/s, the data is transmitted on only two pairs, namely wires 1, 2, 3 and 6. The other two unused pairs, namely wires 4, 5, 7 and 8, can be used to carry electrical current. PoE can "pass" through the wires of the data pairs, this mode of operation is then called "end-point" or through the wires of the unused pairs in 100 Mbit/s in "mid-span" mode.

 

When the connection is established at 1 Gbit/s, all four wire pairs are used for data.