Power over Ethernet (POE) is a technology by which powered devices receive power and signal along a single Ethernet cable. The International Electrical and Electronics Engineers 802 working group is responsible for setting forth the standards governing power over Ethernet applications. The industry has standardized the use of power over Ethernet in order to ensure that devices all work properly together. Earthing, or bonding a piece of electrical equipment to ground, is considered essential to the proper installation of any type of electrical system but becomes even more important when Power over Ethernet enters the equation.
The POE Standards
There are currently two main standards in use for power over Ethernet devices. The first standard, IEEE 802.3af-2003, provides devices with up to 15.4watts of DC power for operation. This translates into approximately 44 volts delivered at 350 milliAmps. The next POE standard, IEEE 802.3at-2009 allows for up to 25.5 watts of power, with some manufacturers claiming as much as 51 watts of usable power can be delivered by their devices. Category 5e data cabling is usually specified for POE applications, and when the installation requires the cable to be run outside, the cable must be rated for outdoor use.
Earthing, or grounding, is defined as the intentional connecting, or bonding, of electrical equipment to earth ground. This is to protect equipment and personnel in case of transient or induced voltages in electrical equipment or wiring. The proper method of earthing an electrical system depends on the size of the system. However, with Power over Ethernet, earthing also protects the equipment from lightning strikes when surge protectors are used properly. POE equipment must be grounded to the same ground that is used by the power sourcing equipment and the building electrical system. The connection to ground needs to be as short and straight as possible, and must be made with a minimum ten gauge bare or insulated copper wire. A quick perusal of a number of POE-related technical support forums shows that improper grounding is one of the main causes of POE systems not working properly and from outdoor equipment receiving irreparable damage during storm activity.
Power Over Ethernet Uses
POE allows you to use powered devices in remote locations. Power over Ethernet allows you to mount parking lot surveillance cameras with pan, tilt, and zoom capabilities and not have to run a separate set of power lines. Wireless modems, access points, and routers can be located wherever needed, whether power is easily accessible or not. Many of the newer Voice over IP phones are powered using POE. Clocks that are synchronized to s central time system, more and more, are using this technology for power and receiving their time signal from the National Observatory Chronometer.
As with any new technology, this one comes with its own terminology. Power sourcing equipment supplies power to the Ethernet cable. The powered device receives power from the PSE through the Ethernet cable. These can be routers, cameras, modems, switches, wireless access points, or and of a number of other device types.