[ Spotlight: Power over ethernet ]
Power over ethernet (PoE) is offering a hot new solution, but you need to be careful with your electrical cables, explains DAVID STEFANOWICZ of the ECA. Here, he considers some of the key issues to be aware of
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ending power and data together over data cables is nothing new. In the late 1990s, some popular companies were installing power distribution over ethernet cables based on their own ‘in–house’ standards.
This led to the Institution of Electrical and Electronic Engineers (IEEE) developing a standard – IEEE 802.3af – in 2003, which allowed the use of 15.4 watts (sending end) of power to be sent down a 100 metre length of four pair Ethernet Category 3 or Category 5 cable.
In the early days, most users of power over
ethernet (PoE) only used a few watts, and there were relatively few problems. However, as time went by, an increasing number of people chose to use the maximum power available (12.95 watts) and this started to show the weaknesses of PoE, by causing undue heating of cables in tight cable bundles, particularly in closed spaces and hot environments. Despite this, the deployment of PoE has rocketed up
58 ECA Today November 2012
It is important to understand what you are buying and how you are installing it
to well over 100 million points in the world today, with relatively few complaints in comparison – and many satisfied customers. However, once the IT industry got used to the idea
of PoE, it decided that it liked the whole idea of only having one set of cables involved and not needing a power socket close by the ethernet device that was being connected. This led to a proliferation of PoE devices and chips being made, some of which did not appear to comply with the IEEE standard. In turn, this led to the IEEE developing the PoE standard further to allow more power to be sent down the ethernet cable.
Standards The new IEEE standard 802.3at, released in September 2009, increased the power available at the powered device (receiving end) from 12.95 watts to 25.5 watts using Category 5e or better data cables. This led to more problems being encountered due to heat accumulation in data cable bundles. In response to this problem, the US Telecommunications Industry Association (TIA), IEEE, International Organization for Standardization/International Electrotechnical Commission (ISO/IEC), ECA and some manufacturers undertook programmes of research to help provide the data industry with better guidance to help prevent cables from overheating. The advice given included using larger data cables,
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