10/100/Gigabit High Power PoE to 1000BASE-SX Media Converter
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6. PoE Technology
Power over Ethernet
or
PoE
technology describes a system to transfer electrical power, along with data, to remote
devices over standard twisted-pair cable in an Ethernet network. This technology is useful for powering IP telephones,
wireless LAN access points, network cameras, remote network switches, embedded computers, and other appliances
where it would be inconvenient, expensive (mains wiring must often be done by qualified and/or licensed electricians for
legal or insurance reasons), or infeasible to supply power separately. It doesn't require modifiying your existing Ethernet
cabling infrastructure.
IEEE 802.3af
(Power over Ethernet), is the specification that allows the powering device to use a voltage between 44–57
VDC, though the nominal voltage is 48V, over two of the four available pairs on a CAT3/CAT5e cable with a selectable
current of 10–350 mA subject to a maximum load power of 15.40W. Only about 12.95W are available after counting cable
losses, and most switched power supplies will lose another 10–25% of the available power.
IEEE 802.3at (
Max. PoE output power consumption up to 30W is an updated standard in progress referred to as PoE plus
or 802.3at) that introduces increases available power. Numerous non-standard schemes were used prior to the PoE
standard to provide Power over Ethernet cabling. Some are still in active use.
The standard describes two types of devices:
Power Sourcing Equipment(PSE) and Powered Devices(PD).
PSE provides power to the PD.
The PoE PSE+ converter may auto-detect PD and provide power via one of two valid four-wire connections. In each four-
wire connection, the two conductors associated with a pair each carry the same nominal current in both magnitude and
polarity. The following figure and the PSE pinout alternative table describe the valid alternatives.
PSE Pinout Alternative Table
PD and PSE Eight-Pin Modular Jack (RJ-45)