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Powering IT devices via the network cable - commonly known as Power over Ethernet (PoE) - is enjoying increasing popularity. IEEE specifications published in 2003 and 2009 permit the device a maximum supply of 12.95 W or 21.90 W. But this is no longer sufficient for many applications today. Various proprietary solutions as well as a standardization project launched at the end of 2013 are now promising 100 W and more.

Does this mean that the end is now in sight for the 230 V power supply of network-powered equipment? Can we soon expect to see notebooks, printers, TVs and similar multimedia devices without tiresome external power supplies? Can data connectors achieve the holy grail of introducing globally standardized electrical plugs through the back door?

What appears at first glance to be the egg of Columbus actually raises a number of questions on closer inspection. What does PoE mean for the communication cable networks which will then be required to transmit such high power levels in addition to their primary purpose of data transfer? Are the data cables which are used able to cope with the resulting thermal load? And what about electrical safety?

The DKE already addressed these and other questions some time ago in the European Committee for Communication Cable Systems. At present too little is known about the effects of the systematic and persistent use of a data cable - or entire bundles of cables - to transmit power. Under German leadership, CENELEC/TC 215 has developed a mathematical model which can be used to calculate the expected warming of cable harnesses. An important aspect is the influence which the temperature increase due to the remote power supply has on the transmission capacity of the communication cable system. The cable attenuation is temperature-related, and so the the use of PoE will significantly reduce the currently standardized path lengths in some cases. Each reduction must be individually calculated based on the cable used and the type of installation.

It has been shown that the target power of 100 W given in the specifications is feasible if certain conditions are met. However, the planners and installers of communication cable systems must comply with additional requirements in order to meet both the desired transmission technical characteristics and at the same time provide a power supply in the range of 75 W to 100 W. Appropriate new requirements and recommendations for this are currently being prepared and are to be added to the existing standards.

One thing is, however, already clear: no world-wide harmonized electrical plug will be introduced for Power over Ethernet.

Wegmann, Thomas
+49 69 6308-315