On Power Supply and Wire Sequence of PoE Switches

PoE power is delivered over Ethernet cables, which have 4 twisted pairs. The IEEE802.3af/at standards allow PoE to supply power in three wire sequence configurations:

　　1. Pins 4 and 5 are positive, pins 7 and 8 are negative;

　　2. Pins 1 and 2 are negative, pins 3 and 6 are positive;

　　3. Pins 1 and 2 are positive, pins 3 and 6 are negative;

　　Note: In 10M and 100M PoE switch data networks, only two pairs (1, 2, 3, 6) are used for data signal transmission, while in Gigabit PoE switch networks, all four pairs are utilized. This is also one of the differences between 100M and Gigabit PoE switches.

　　10/100 DC on Spares (mode B): Power supply over spare pairs in 10M/100M networks

　　10/100 Mixed DC &Data (mode A): Power supply over data pairs in 10M/100M networks

　　1000 (1 Gigabit) DC & Bi-Data (mode B): Gigabit network mode B, power supply over pins 4, 5, 7, 8

　　1000 (1 Gigabit) DC & Bi-Data (mode A): Gigabit network mode A, power supply over pins 1, 2, 3, 6

　　Tx represents data transmission, Rx represents data reception, and TxRx represents both transmission and reception.

　　The table above shows the wire sequences for IEEE 802.3af and IEEE 802.3at. Please note that pins 4 and 5 are always positive in both af and at standards. If a product has pins 4 and 5 as negative, it is a non-standard PoE product. In 802.3at 4 pairs mode, all four pairs supply power, with PSE output power up to 60W and PD receiving power above 51W.

　　568A Color and T568B Color have slight differences. According to international standards, there are two wiring arrangements for Ethernet cables: 568A and 568B. Normally, the 568B standard is more commonly used, with the wiring order: 1 white-orange, 2 orange, 3 white-green, 4 blue, 5 white-blue, 6 green, 7 white-brown, 8 brown (swapping 1 and 3, and 2 and 6 respectively gives the 568A standard). 568A and 568B have no essential difference, only a difference in color. The essential requirement is to ensure:

　　(1) Pins 1 and 2 form a twisted pair

　　(2) Pins 3 and 6 form a twisted pair

　　(3) Pins 4 and 5 form a twisted pair

　　(4) Pins 7 and 8 form a twisted pair

　　However, to avoid errors during project installation, it is recommended to use the T568B wiring method.

　　Currently, PoE power is typically implemented by purchasing PoE switches or PoE power injectors. There is no need to deliberately understand the PoE power supply wire sequence issues. For any questions regarding PoE power supply, PoE switch selection, and solutions, please consult the Raytrans technical department.