Everything You Need to Know About IEEE PoE 802.3bt

Power over Ethernet
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Why Power over Ethernet (PoE)? 

Power over Ethernet (PoE) offers many advantages over traditional power methods, including time and cost savings, flexibility, safety, reliability ,and scalability. The main drawback has been the limited amount of available power. Initially, 15.4W of power was sufficient for IP phones and other simple applications at the time, but as more complex applications entered the market, there was an increasing demand for more power.

In 2009, the Institute of Electrical and Electronic Engineers (IEEE) released IEEE 802.3at, specifying 30W of power at the PoE source. Today, the IoT market is expanding at such a rapid rate that even higher power is needed to support additional devices connected to the Ethernet network, such as connected lighting, small cells, and 802.11ax access points.

What Is 802.3bt?

To address the need for more power, the IEEE introduced IEEE 802.3bt in 2018. It expands the maximum PoE power available, pushing the power limit of power sourcing equipment (PSE) to 90W and powered devices (PDs) to 71.3W. This new standard achieves this by utilizing all four pairs of the structured wiring. Additionally, IEEE 802.3bt supports multiple PoE classes and is backwards compatible.

The key features introduced in the new 802.3bt standard include:

  • Type 3 and Type 4 PSE/PD
  • Support for two PD constructions: single-signature PD and dual-signature PD
  • Utilizes four pairs
  • Additional classes—class 5 to class 8—and improved mutual identification process
  • Automatic class functionality
  • Extended power capability, if channel length is known
  • Low standby power support
  • 10G-BaseT with PoE
  • Complies with the limited power source and safety extra low voltage (SELV) requirements as defined in ISO/IEC 60950

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802.3bt replaces all existing pre-standard solutions and will likely be the maximum level defined, as levels higher than 90W could be unsafe for existing cabling infrastructures.

How Does It Impact the Market?

With more power comes more opportunities. Support for higher power with PoE enables new markets to emerge and expands application options within existing markets. As the standard is adopted, we’ll begin seeing it implemented in applications that require more power, such as smart buildings and smart cities.

Andrew Jimenez

Andrew Jimenez is the vice president of technology at Anixter. He has worked in the telecommunications industry for more than 25 years and is an active voting member of the TIA TR-42 Telecommunications Cabling and IEEE 802.3 LAN/MAN standards committees.