Power Management Features and Integration
Most advocates expect PoE to become a global longterm DC power cabling standard and replace "wall wart" converters, which cannot be easily centrally managed, waste energy, are often poorly designed, and are easily vulnerable to damage from surges and brownouts.
Critics of this approach argue that DC power is inherently less efficient than AC power due to the lower voltage, and this is made worse by the thin conductors of Ethernet. A typical 48-port Ethernet switch has a 50 W to 80 W power supply allocated for the traditional Ethernet switch and transceiver IC. Over and above this it requires typically a 370 W (for 802.3af) to 740 W (for 802.3at) power supply allocated solely for PoE ports, permitting a maximum draw on each. This can be quite inefficient to supply through long cables. However, where this central supply replaces several dedicated AC circuits, transformers and inverters, and prevents expensive human interventions (AC installations) the power loss of long thin DC cable is easily justifiable. Power can always be introduced on the device end of the Ethernet cable (radically improving efficiency) where AC power is available.
Read more about this topic: Power Over Ethernet
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