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IEEE 802.3AF Power Over Ethernet

This Standard was approved for publication in June of 2003 and describes means to economically provide power over a twisted-pair link segment to a single Ethernet device by specifying the voltage and minimum and maximum current and wattage necessary to provide power concurrently with 10BASE-T, 100BASE-TX, and 1000BASE-T signaling. Although the Standard specifies compatibility with category 3 and category-5e structured cabling, supplying power over Ethernet is recognized to also be compatible with category 6 and category 7 cabling. The specified methodology is compatible and interoperable with compliant RJ- 45 MDI (media-dependent interface) Ethernet devices including switchto-switch connections (both supplying power), cross-over cables, and common mode termination implementations. The following applications directly benefit from power application over MDIs:

  • IP Telephony
  • Web Cameras
  • Wireless Access Points
  • Industrial Automation
  • Home Automation
  • Security Access Control and Monitoring Systems
  • Point of Sale Terminals
  • Lighting Control
  • Gaming and Entertainment Equipment
  • Building Management

There are two locations where power can be introduced: endpoint or mid-span. Endpoint power (a.k.a. phantom power) is introduced via the active equipment as shown in figure 1 below.

Figure 1

Mid-span power is introduced in the Telecommunications Room (TR) between the patch panel and switch as shown in figure 2 below.

Figure 2

Power may be applied over the pairs in one of three possible schemes as shown in table below.

Conductor Alternative A (MDI-X) Alternative A (MDI) Alternative B (All)
1 - VPort + VPort
2 - VPort + VPort
3 + VPort - VPort
4 + VPort
5 + VPort
6 + VPort - VPort
7 - VPort
8 - VPort

IEEE 802.3af Powering Options

Endpoint power can be applied using alternatives A, B or both. It is important to note that, while active equipment may be capable of both alternatives A and B, they are not to operate both alternative A and alternative B on the same link segment simultaneously. Mid-span power application is limited to alternative B and 10/100 applications only. Refer to the Siemon Q&A entitled, "Powered Ethernet" for additional information.

Recent developmental work within the IEEE committee supports expansion of the original scope of this Standard to evaluate proposals that will result in increased power carrying capability over the cabling infrastructure.