Enterprise networks continue to expand, growing more versatile and complex. Devices once considered peripherals such as wireless access points (WAPs), security network cameras, building automation and control systems, and voice-over-IP (VoIP) phones are now important network assets.
As more devices are added, the cabling infrastructure needed to support them grows, and the option to power them over network cabling becomes more attractive.
Power over Ethernet (PoE) has emerged as a key powering strategy, allowing network managers, installers, and integrators to use structured cabling to provide both power and data to many of their network devices. The original PoE standard, IEEE 802.3af, limited the technology to devices requiring less than 12.95 watts of power.
A revised PoE standard, IEEE 802.3at (also known as PoE Plus or PoE+) was adopted in 2009 and raised the PoE power supply to 25.5 watts. Since then, the industry’s interest in, and demand for, higher power PoE solutions has continued to snowball.
The next evolution of PoE is IEEE 802.3bt, and is intended to deliver up to 100 watts of power to PoE enabled devices. This implementation will use all four pairs of the cable
PoE describes a system to safely transmit electrical power, along with data to remote devices over standard Category 5e, 6 and Category 6A cabling. PoE is designed so Ethernet data and power signals do not interfere with each other, thereby enabling simultaneous transmission without signal disruption.
Power over ethernet works by converting the mains power supply into a low-voltage supply, then transmitting the power over structured cabling to PoE-enabled devices. Some power dissipation is inevitable. For example, systems meeting the PoE 802.3at standard introduce 15.4 watts of power on the cabling, but only 12.95 watts can be expected to be received by the PoE device.
As the power rating being applied to 4 pair cables increases, the effects of temperature change needs to be considered. When remote power is applied to balanced cabling, the temperature of the cabling will rise due to heat generation in the copper conductors.
Depending on the installation conditions, the heat generated will be dissipated into the surrounding environment until a steady state is reached with the temperature of the cable bundle higher than the ambient temperature of the surrounding environment. The temperature of any cable in the cable bundle should not exceed the temperature rating for the cable. This is covered in detail in a number of cabling standards including ISO TR29125 and TIA TSB184-A.
Consideration must be also given to the continuous current handling capability of the connecting hardware and outlet connector. The connecting hardware and outlet connector should be able to handle the maximum allowable current for both the existing 802.3at standard and the expected 802.3bt standard.
If you want to learn more about power over ethernet (PoE) see this white paper: http://www.commscope.com/docs/poe_groundwork_wp-107291.pdf