Power over Ethernet enables a power supply via Ethernet cables that are already in use. Power over Ethernet offers several advantages:

  1. Cables can be used twice and therefore save space and costs
  2. Independence from already laid power lines
  3. Saving of power adapters and power supplies by using centralized switches

PoE is divided into 3 different standards:

IEEE 802.3af PoE

This standard can, by using the two free wire pairs in 10Base-T and 100Base-TX network cables, provide up to 15.4 watts and has a maximum voltage of 48 volts. If transmission via these wire pairs is not possible, the signal-carrying wires can also be used. However, only 12.95 watts arrive at the end device due to losses. It supports category 3 and 5 cables.

IEEE 802.3at PoE+

This standard, on the other hand, enables higher power through endspan and midspan supply. In the endspan method, a PoE switch provides the supply. The midspan method, on the other hand, requires an intermediate source such as a PoE injector.

Power transmission is possible via phantom power or spare pair power. Phantom power transmits the current via the wire pairs used for data transmission. Spare pair powering, on the other hand, uses only unused wire pairs.

IEEE 802.3at allows up to 25.5 watts at the end device and only supports Category 5 cables.

IEEE 802.3bt 4PPoE

This standard provides power from 40 watts up to 100 watts through five power levels. 960 milliamperes flow over each pair of wires used. Only two wire pairs (category 5) or all four wire pairs (category 8) can be used. IEEE 802.3bt 4PPoE delivers 90 W of output power, of which up to 71.3 W arrives at the end device.

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