page_title: Power over Ethernet
section_title: Power management features and integration
hierarchical_section_title: Power over Ethernet / Power management features and integration
caption_attribution_description: English: Image is actually of a Nortel 5520-48T. Image is actually of a Nortel 5520-48T.
context_page_description: Power over Ethernet, or PoE, describes any of several standards or ad hoc systems that pass electric power along with data on twisted pair Ethernet cabling. This allows a single cable to provide both data connection and electric power to devices such as Wireless Access Points, Internet Protocol cameras, and Voice over Internet Protocol phones.
  There are several common techniques for transmitting power over Ethernet cabling. Three of them have been standardized by Institute of Electrical and Electronics Engineers standard IEEE 802.3 since 2003. These standards are known as alternative A, alternative B, and 4PPoE. For 10BASE-T and 100BASE-TX, only two of the four signal pairs in typical Cat 5 cable are used. Alternative B separates the data and the power conductors, making troubleshooting easier. It also makes full use of all four twisted pairs in a typical Cat 5 cable. The positive voltage runs along pins 4 and 5, and the negative along pins 7 and 8.
  Alternative A transports power on the same wires as data for 10 and 100 Mbit/s Ethernet variants. This is similar to the phantom power technique commonly used for powering condenser microphones.
context_section_description: Advocates of PoE expect PoE to become a global long term DC power cabling standard and replace a multiplicity of individual AC adapters, which cannot be easily centrally managed. Critics of this approach argue that PoE is inherently less efficient than AC power due to the lower voltage, and this is made worse by the thin conductors of Ethernet. Advocates of PoE, like the Ethernet Alliance, point out that quoted losses are for worst case scenarios in terms of cable quality, length and power consumption by powered devices. In any case, where the central PoE supply replaces several dedicated AC circuits, transformers and inverters, the power loss in cabling can be justifiable.
caption: Avaya ERS 5500 switch with 48 Power over Ethernet ports
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