x600 Series Layer 3 Gigabit Ethernet Switches Installation Guide
PSU installed in the
However, the maximum possible PoE+ power requirement (24 ports x 30W ~ 720 watts) is above the maximum amount of power available (370W) for the PSU installed in the
Implementation 10/100BASE-TX
An Ethernet cable has four twisted pairs, but only two of these are used for data transfer. Note that both the
The spare pairs are used. In this case the unused pairs are used to transfer the power. The twisted pair on pins 4 and 5 is connected to form the positive electric power supply, while the twisted pair on pins 7 and 8 is connected to form the negative power supply. Each pair can accommodate either polarity.
The data pairs are used. The twisted pair on pins 3 and 6 and the pair on pins 1 and 2 can be of either polarity. Since Ethernet pairs are transformer coupled at each end, it is possible to apply DC power to the centre tap of the isolation transformer without upsetting the data transfer.
The IEEE 802.3af and IEEE 802.3at standards do not allow both sets of wires to be used, so a choice must be made. Different vendors PSE equipment may use one or other of the methods to supply power depending on PoE implementation. The Powered Device (PD) should be able to accept power from both options.
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