A standard CAT-5 UTP Network cable consists of 4 pairs of wires. Only 2 of these pairs are used in a normal network configuration. Power over Ethernet for network cameras uses the 2 spare pairs of wire to transmit power to the end device, usually a network camera or other ethernet device. In order to avoid voltage drop along the cable (up to 100 metres), 48 volts DC is ?injected' into the hub end and then split off by a regulated DC-DC converter at the device end into the required voltage. There is an IEEE 803.af standard for power over ethernet but there are several different ways of achieving it: A simple point-to-point pair (injector and splitter). This can be used to provide power to any device listed on the website which has Optional PoE. If a camera is not listed as having optional PoE, it may be because the device requires more power than can be provided by PoE, eg some Pan-Tilt-Zoom cameras. A Power Over Ethernet Hub can be used to provide the injector and network combination for multiple devices - this is often called a mid-span PoE hub. At the device end, you will need either a camera which has a built-in splitter, or you will need to purchase a separate splitter of the correct voltage. A device with a built-in PoE splitter - this requires either a mid-span PoE hub to provide the input power, or a simple PoE injector. Power over Ethernet for network cameras is a very useful technology.