Transmitting power and data through a single twisted-pair cable – known as Power over Ethernet (PoE) – is one way to for schools to reduce project installation costs and support integration.
Just a few years ago, devices in schools that required PoE connections were low-wattage devices like VoIP phones, wall clocks, access control systems, lighting controls, etc. Today, however, devices like IP cameras and wireless access points (WAPs) are requiring higher power levels. Soon, devices for digital signage (TV monitors), videoconferencing systems and laptops will be calling for Power over Ethernet connections as well.
A new PoE standard is in development and will address this issue: IEEE 802.3bt will support up to 100W of power per cable. To support power requirements greater than 30W, the IEEE 802.3bt standard calls for use of all four wire pairs vs. just two pairs, which is what the current PoE standard calls for.
With higher power levels come new cable considerations. This new PoE standard (also sometimes called universal, enhanced, PoE++ or 4PPoE) offers schools great flexibility regarding the types of devices that can connect, but also makes cable selection and installation extremely critical. If the cable gets too hot while delivering power and data to these devices over four pairs, performance will suffer – and cabling may experience damage.
Here are three ways that 4-pair PoE will impact school cabling infrastructure – and advice on how you can head off potential problems.
When power is delivered through cabling, heat is generated within the cable. Maintaining the temperature of cabling is important in order to keep insertion loss low and reduce the likelihood of bit errors (as well as prevent cable damage). Minimizing the cable temperature rise can provide several benefits:
How to prevent cable heat rise:
To prevent heat rise from affecting your school’s cabling infrastructure, look for cables that offer the highest operating temperature rating possible with low DC resistance. Category 6A cabling offers low DC resistance and high operating temperature ratings.
Most installed category cables can support 4-pair PoE; however, tightly bundled sizes may have to be restricted depending on cable gauge. Cable bundles should be kept to a net temperature increase of below 15 degrees C (per TIA TSB-184:2009). Keeping temperature rise below this level in tight cabling bundles ensures proper transmission performance and prevents degradation of cable.
How to determine proper cable bundling sizes:
Cable needs access to airflow – without it, heat can’t dissipate. Know the maximum bundling sizes for the cabling you’re using by referring to the manufacturer. Guidance will be also given in the upcoming TIA TSB-184-A, Guidelines for Supporting Power Delivery Over Balanced Twisted-Pair Cabling. The use of Category 6A cables is the best choice, as they allow higher power levels to be delivered to devices while maintaining an acceptable temperature rise inside a cable bundle.
When unplugging a device with a live Power over Ethernet connection, an arc (spark) will occur between the plug and jack contacts if the remote device is still active. Although the user isn’t in danger, arcing may cause problems with the connection, and possibly damage the points on the jack and plug contacts.
How to prevent damage from arcing:
The connectors you choose should follow testing standards IEC 60512-9-3 and IEC 60512-99-001. This will ensure that, when arcing occurs, it won’t damage the plug and jack mating point. Make sure to also power down remote devices during moves, adds and changes (MACs).
Is your cabling system ready to support 4-pair PoE and the higher power it can produce? Belden 10GXS Category 6A smaller-diameter cable delivers more than 100W for full 100 m channels. It supports 10GBASE-T and provides uniform heat dissipation, while a small outside diameter reduces cable space and weight by 25%.
Learn more about the Belden solutions that support 4-pair PoE here. And make sure to watch our recent webinar on Power over Ethernet to learn more about the real-world implications of deploying higher-wattage PoE on twisted-pair cabling.
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