Power over Ethernet (POE)

Power over Ethernet (PoE)

Power over Ethernet (PoE) allows both data and power to be sent across
the same twisted-pair cable, eliminating the need to provide separate power
connections. This is especially useful in areas where installing separate
power might be expensive or difficult.

PoE can be used to power many devices, including:
• Voice over IP (VoIP) phones
• Security cameras
• Wireless access points
• Thin clients

PoE was originally formalized as 802.3af, which can provide roughly 13W
of power to a device. 802.3at further enhanced PoE, supporting 25W or
more power to a device.

Ethernet, Fast Ethernet, and Gigabit Ethernet all support PoE. Power can be
sent across either the unused pairs in a cable, or the data transmission pairs,
which is referred to as phantom power. Gigabit Ethernet requires the
phantom power method, as it uses all eight wires in a twisted-pair cable.

The device that provides power is referred to as the Power Source
Equipment (PSE). PoE can be supplied using an external power injector,
though each powered device requires a separate power injector.

More commonly, an 802.3af-compliant network switch is used to provide
power to many devices simultaneously. The power supplies in the switch
must be large enough to support both the switch itself, and the devices it is
powering.