Electrical Contracting News (ECN) December 2016 - Page 38

SPECIAL FEATURE DATA CABLING CAUSE 4 THOUGHT Power over Ethernet (PoE) combines energy and data transmission, allowing network devices to be powered using copper data cabling. This helps reduce installation costs, simplifies UPS implementation to raise QoS levels and makes ongoing maintenance easier and cost effective. The latest version – 4PPoE – increases available power levels and allows more demanding terminal equipment to be powered via network cables. There are, however, some things to consider when introducing 4PPoE. Matthias Gerber of Reichle & De Massari explains. W hen the PoE standard was introduced a decade ago it supported up to 15W. PoEP, introduced in in 2009, supported up to 25W. The latest version, as described in the IEEE 802.3bt standard, uses all four twisted-pairs in the network cabling for energy transfer, hence its name: 4-pair Power over Ethernet (4PPoE). 4PPoE can power devices over 100m of data cable, and has the potential to make separate power cabling to sizeable devices obsolete. It can supply at least 55W of power in level 3 mode and up to 90W in level 4 – three to four times more than the current rate. Defeating the heat For 4PPoE level 3 and level 4 every twisted-pair in the network cabling carries a current of between 650 and 1,100mA. A significant load compared to using cables exclusively to transfer data. This increase in power does cause twisted-pair copper cables and bundles to heat up, reducing the possible transmission range. The resulting temperature increase is not without side effects. As a rule of thumb, a long term 10ºC temperature rise halves the life expectancy of the materials used in the cables. Also, the temperature increase must be monitored and managed for fire and occupational safety reasons. This potential temperature increase needs to be taken into account from the very beginning of a cabling project. That introduces new challenges when installing data networks. The elevated temperatures increase resistance. In turn, the signal is increasingly attenuated, reducing the possible length of a link. In the worst case, data transmission may even become altogether impossible at high temperatures even though it would work fine at room temperature. Therefore, the cabling has to be planned in accordance with the expected temperatures, should 4PPoE be used, and the overall link length has to be adjusted to the assumed conditions. Thick cable bundles heat up the cables at the centre of the bundle. What’s more small diameter cables lead to higher temperature increase. We recommend using cables with larger conductor crosssections and avoiding large cable bundles during installation. Shielded cables can support longer cabling links as the cable shield helps to dissipate the heat from inside the bundle and reduces the temperature increase. For example: Category 5e installation cables with an AWG 24 (0.22mm2) conductor cross-section reach their ‘natural limits’ quite quickly. Temperature grows rapidly, especially when they are used in large cable bundles. A reduction of the link length is often necessary under these conditions. With Categorty 6 cables (AWG 23) temperature increase is not so much of an issue and the length of the permanent link can normally reach the full 90m length. Small sparks, big problems Cables should be terminated to modules and plugs as securely as possible to prevent heat up under 4PPoE use. Insulation displacement technology, for example, is ideally suited for this application. The widely used piercing technology, on the other hand, penetrates only the insulation of the copper cables and creates a loose contact. Over time, the termination can grow less reliable and in the worst case this can result in the destruction of the connection. ‘Using larger diameter cabling for 4PPoE has clear benefits in the area of diminishing cable resistance, thereby preventing power losses.’ It’s worth noting, that disconnecting ‘live’ contacts may damage them. The small spark resulting from disconnection can destroy part of the contact when under increased load, potentially permanently impairing its quality of contact (spark erosion). Plug and connection modules should be designed in such a way, that sufficient distance between breaking point (where the spark and potential damage occurs) and nominal contact area are ensured. Energy savings, IoT and cooperation Using larger diameter cabling for 4PPoE has clear benefits in the area of diminishing cable resistance, thereby preventing power losses. This not only reduces the environmental impact of PoE, but can also deliver savings to operators of large networks. As the number and size of data facilities and LANs continues to grow exponentially, every option for energy saving, however small, can help. Soon, structured cabling systems will no longer be used exclusively to transport data at up to 10G, but also to power numerous IP terminal devices, from monitors to wireless access points. This is in line with developments around the Internet of Things – lots of sensor equipped devices can be hooked to the structured cabling backbone and powered at the same time. Creating a cabling system for PoE and PoEP using realistic framework conditions is a straightforward task, since transmission length restrictions rarely need to be taken into account. However, if structured cabling is also to be suitable for future 4PPoE planners/consultants, installers and suppliers need to closely cooperate in order to ensure 4PPoE compliance. 38 | December 2016 38 Data Cabling – R&M.indd 38 11/11/2016 16:42