WHAT IS POE?

Power over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling. PoE requires category 5 cableor higher for high power levels, but can operate with category 3 cable for low power levels.^[1] Power can come from a power supply within a PoE-enabled networking device such as an Ethernet switch or can be injected into a cable run with a midspan power supply.

The IEEE 802.3af-2003^[2] PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA^[3][4]) to each device.^[5] Only 12.95 W is assured to be available at the powered device as some power is dissipated in the cable.^[6]

The IEEE 802.3at-2009^[7] PoE standard, also known as PoE+ or PoE plus, provides up to 25.5 W of power.^[8] Some vendors have announced products that claim to comply with the 802.3at standard and offer up to 51 W of power over a single cable by utilizing all four pairs in the Cat.5 cable.^[9] Numerous non-standard schemes had been used prior to PoE standardization to provide power over Ethernet cabling. Some are still in active use.