Power-over-Ethernet

What is Power Over Ethernet?

Power Over Ethernet (PoE) technology describes any system that transmits electrical power, in addition to data, to remote devices over standard twisted-pair wire in an Ethernet network. This technology is useful for powering network devices where it would be inconvenient or infeasible to supply power separately. Such devices include IP telephones, wireless LAN access points, IP cameras, IP sensors and instruments in industry, IP radios, digital clocks, and more. The technology is comparable to POTS telephones, which also receive power and data (although analog) through the same cable.

PoE works without requiring modification to the existing Ethernet copper cabling infrastructure. Power over Ethernet is standardized in IEEE 802.3af. The IEEE 802.3af-compliant power sources supply 48 volts DC to devices at a maximum current of 350 mA. This allows devices to draw up to 15.4 watts.

A twisted-pair Ethernet cable contains four pairs of wires. The Ethernet RJ-45 10/100Mb twisted-pair cable standard uses two of these pairs for data. The 802.3af standard allows power transmission over the two unused pairs, or the two data pairs. To prevent damage to devices that don't accept power over Ethernet, an 802.3af power source won't begin sending power until a remote device acknowledges that it can accept power. (Ref. Wikipedia)

The GarrettCom Magnum PS14P is a 4-port PoE heavy duty Ethernet Switch for Industrial PoE applications.

More general information on Power Over Ethernet, see web sites such as:

www.PowerOverEthernet.com
www.altair.org/labnotes_POE.html