Power Over Ethernet- Up to 51 W of power over a single cable by utilizing all four pairs in the Category 5 cable


Xmultiple's Engineering Department

Power over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling. PoE provides both data and power connections in one cable, so equipment doesn't require a separate cable for each need. For equipment that does not already have a power or data connection, PoE can be attractive when the power demand is modest. For example, PoE is useful for IP telephones, wireless LAN access points, cameras with pan tilt and zoom (PTZ), and remote Ethernet switches. PoE can provide long cable runs e.g., 100 meters (330 feet) and deliver 12 W of galvanically isolated power. PoE-plus provides even more power.

The IEEE standard for PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable if less power is required. Power is supplied in common mode over two or more of the differential pairs of wires found in the Ethernet cables and comes 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 original IEEE 802.3af-2003[PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA to each device. Only 12.95 W is assured to be available at the powered device as some power is dissipated in the cable.

The updated IEEE 802.3at-2009 PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power. The 2009 standard prohibits a powered device from using all four pairs for power. Up to 51 W of power over a single cable can be achieved by utilizing all four pairs in the Category 5 cable.

Numerous non-standard schemes had been used prior to PoE standardization to provide power over Ethernet cabling. Some are still in active use


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