Power over Ethernet (PoE) combines both data communication and power transmission for remote devices in the one cable, therefore eliminating the need to run a separate cable to power a device.
Increasingly used for VOIP phones, wireless access points (WAP’s) and IP cameras, PoE eliminates the need for a nearby power outlets for these powered devices and allows a single cable to provide both data connection and electrical power. PoE is also being used in Smart Homes to control and power LED lighting, sensors, control panels, clocks and high power PoE can even be used to charge laptop batteries.
USB also has this capability, PoE differs by being suitable for cable lengths of up to 100m and uses the standard RJ45 plug and network cable.
The PoE power is supplied by either a network switch/router or PoE injector.
How does PoE Work?
A network data cable does not require all 8 wires contained in the cable for a data connection. So, an unused pair of wires are used to carry the Direct Current (DC) voltage to the end device.
An Ethernet network cable has 8 wires and the blue and white/blue wires (pins 4 and 5) are used for the positive voltage (V+) and the negative voltage (V-) uses white/brown and brown wires (pins 7 & 8 on the RJ45 plug).
The PoE voltage is between 44 – 57VDC. Typically 48V is used in most devices.
There are different flavours of PoE and they are all defined in IEEE 802.3af that was originally developed in 2003. Now there is standard PoE, PoE+ that delivers more power to the end device, PPoE and type 4 PPoE. The table below shows the differences between the different standards.