ISE Magazine, August 2018
I S E I C T S O L U T I O N S E D U C AT I O N 2 4 POE ture rating for 60W or higher PoE The TIA is also developing guidelines for limiting temperature rise in a bundle Following a fact finding study to investigate the effects of higher levels of PoE applied over cables in a bundle Underwriters Laboratories UL introduced a Limited Power LP Certification to help simplify cable choice for PoE applications The LP certification indicates that a cable has been tested to carry PoE under worst case installation scenarios without exceeding the temperature rating of the cable The certification accounts for large bundle sizes high ambient temperatures and other environmental effects such as enclosed spaces or conduits Its important to understand that LP is a certification not a listing or a rating So unlike other UL listings or plenum or riser ratings that are required by the NFPA 70 National Electric Code LP certified cable is an option not a requirement And speaking of the NEC the 2017 edition contains new requirements that also address the heat rise issue but only when power is greater than 60W Type 3 For these cases NEC includes ampacity tables that specify the maximum ampacity allowed for a certain cable bundle size conductor gauge and cable temperature rating installed in an ambient temperature of 30 C 86 F Because the NEC is law complying with these ampacity tables is required However the NEC does allow the use of an LP certified cable as an alternative to following the ampacity table The good news is that you only need to worry about this issue if youre planning to run PoE above 60W and most PoE enabled devices including LED lights require less than that The bad news is that you never really know how much power might eventually be delivered over the cable so following ampacity tables or using LP certified cable is a good method for future proofing Other options include using cables with larger diameter conductors higher temperature ratings or shielded construction as well as simply choosing to not use cable bundles While DC resistance unbalance is not typically an issue in higher quality cables that would have a higher temperature rating or LP certification poor workmanship can still cause too much resistance unbalance Therefore it is still recommended that LP cabling be tested for DC resistance Modular Plug Terminated Links With the Internet of Things IoT and the development of sensor technology more and more devices are becoming IP enabled and connecting to the copper horizontal cabling infrastructure Most of these devices such as LED lights security cameras building automation controls and Wi Fi access points Figure 2 4 Pair Type 3 and Type 4 PoE 48V 1 2 3 6 4 57 8 1 2 3 6 4 57 8 DC DC Converter PSE PD Figure 3 Modular Plug Terminated Links are employed in places where an extra patch cord is not convenient
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