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Heating Effects for Remote Power Delivery Over Bundled Cables

How much power can be delivered from the Power Sourcing Equipment to the Powered Device without overheating the cables?

What Is This White Paper About?

There is a lot of interest in the industry about the power handling capability of different cables to power up devices that can consume up to 60 Watts or more of power. Some applications, for example HDBASET are looking at the capability of delivering up to 100 Watts of power for audio/video devices such as HDTV monitors. But there is a concern regarding the heating effect resulting from the current that is flowing in the cables to power up these devices.

The official position in the industry is the IEEE 802.3at Power over Ethernet Standard that specifies a Power handling capability for Type 2 operation of 25.5 Watts over 2 pairs of Category 5e cabling and potentially up to 60 Watts when powering over 4 pairs using Category 6 and Category 6A cables. TIA has also published a Telecommunications Systems Bulletin (TSB-184) that supplements the information contained in the IEEE 802.3at Standard regarding cable bundling, temperature rise and current capacity.

In order to answer this question a controlled experiment was performed to evaluate the temperature rise in a cable bundle when delivering different amounts of DC power to the powered device over Category 5e, Category 6 and Category 6A cables.The results of the heating study show that the maximum power delivery when all pairs are energized is between 50 to 80 Watts for a 100 cable bundle depending on the cable design

This White Paper covers the topics of:

  • How much power can be delivered from the Power Sourcing Equipment (PSE) to the Powered Device (PD) without overheating the cables?
  • Resistive Heating and Remote Power Delivery
  • Thermal Time Constant
  • What is the temperature rise for different cable types and different size cable bundles?
  • The effect of "temperature rise" on transmission performance