Power over Ethernet (PoE)

Providing power to apparatus over network cables has always been usual practice for fixed-line telephones, and now the same capabilities are becoming available on wired Ethernet. The IEEE 802.3af PoE (Power over Ethernet) standard allows up to 13 watts to be supplied and its successor, PoEPlus (802.3at), allows up to 30 watts. In this article we look at how it works in theory and in practice.