What is PoE (Power over Ethernet)

Written by

Michael Roden

GetVoIP Staff Member

Michael Roden is GetVoIP.com’s news reporter and VoIP provider analyst. Mike currently resides in Brooklyn, NY, all the while neglecting his Mother’s wish that he keep his wallet in his front pocket. He finds the most solace in the arts, humanities, music, & culture – with the same fervor and fascination Aristotle had for the stars. There are few things that may upset Mike, but none more than when Paris Hilton tries to DJ.

August 20, 2012

Power over Ethernet is a way to power network devices over the Cat5/Cat6 cable rather than use an AC outlet. Power over Ethernet requires only one cable to carry both data and power. By deploying PoE-compatible devices, companies can save time, money and space. Devices are designed to be either PoE-compatible or non-PoE incompatible, but non-PoE compatible devices can be converted with a device called a “picker.”

PoE devices are usually used to power wireless LAN access points. It can cost between $100 and $200 for a professional to run an Ethernet cable to a wireless access point. But, it can actually cost $400 for run electric wire safely to that same point. In addition, with two cables, that doubles the chances that something can go wrong and need to be fixed or replaced. PoE is also ideal for IP phones and security cameras. Power over Ethernet continues to function in the event of a blackout, so long as there is backup battery power.

Electricity is first “injected” into a Cat5/Cat6 cable through “power sourcing equipment” (PSE), such a specialized network switch. A PoE-compatible device, if plugged in this way, will function normally, in much the same manner you can charge and program your iPhone using its USB cable. If the device is not PoE compatible, a second device, called a “picker,” will “pick off” current and route the current safely to the device’s regular power jack.

PSEs have several different design configurations. The devices can have up to 48 gigabit ports, which means they can send data and power to 48 devices. If a device is “managed,” it means it can be remotely shut down over the internet using a web browser. An Ethernet switch with power sourcing equipment built in is called an endspan. A power injector that stands between the switch and the powered device that injects power into the cable is called a midspan.

A PoE cable can be up to 660 feet (100 meters), but it can also be extended using additional, smaller, switches. A PSE can power devices in one of two modes, called A or B. In mode A, the data and the power are sent along the same wires within the cable; in mode B, the power is sent along two wires within the cable that were otherwise not used. A PoE-compatible device must accept both mode A and mode B.

Power over Ethernet is an evolving technology, and some non-standard configurations are on the market. Time will tell if these configurations become recognized as a standard, or are abandoned.