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New National Electrical Code 2017 Requirements affect POE wiring.

By Steven deSteuben, Mar 7 2017 03:06AM

Are you getting ready to wire up your new office or gathering quote for your next installation? Be sure to ask the question from your vendors what they are planning to do to meet the NEC 2017 Requirements for "power limited" cabling that would effect all POE installations.


At the time of this writing only Massachusetts has adopted the NEC 2017 requirements. However, many other states have started the process to merge over to these standards. Soon enough it will be required for all installations.


What is this new requirement and how does it affect POE installations?


To summaries what you are about to read, We suggest if you are going to use POE++ devices in the future then you should select a Cat 6 or Cat 6A cable that has a PL rating for the max wattage of your POE Devices.


POE devices receive power over the Ethernet cabling (POE). Depending on the the equipment this voltage that is sent might be 24V - 48V. Until recently the wattage of these devices was rather small. Because of that there was no real requirements in terms of POE devices, at least not technically. However, starting in 2017 the NEC has realized that there are much more power hungry devices out there, or soon to be out there, on the market. This increase in power and wattage means the cablings carrying this power will produce more heat and will have a potential fire risk. This is particularly the case the larger your bundle of cables is in the ceilings, in your cable trays, and in the racks.


That extra heat from the cabling could do a few things. First, it could actually melt your Ethernet cabling, causing it to short out and fail. If you have higher wattage in the cable, and it shorts out on the metal basket tray, or inside a peice of metal conduit, it could actually start a fire. Second thing that could happen, is the cabling could heat up to a point that it begins to heat up something in the wall, or ceiling around the cabling, causing the other material to catch fire, or melt.


Nec 2017 725.144 require cabling carrying the new POE++ devices to have a either a cable with a rating stamped on it that says "PL" (power limited) followed by its designed wattage, or you must prove to the inspector the wattage calculation of your devices, and the burn / melting temperature rating of your cabling. This is a combination of the fire rating of the cabling and the AWG (gauge) of the cable.


Regardless of the above ratings you will then also be limited to the number of cables in your bundles based on the type of cable.


For example. If your new network will have POE ++ devices with 70 watts of power, you will need to consider the type of cabling being installed. If your contractor wants to save money and use a cat 5e cable that is very very cheep, it may have 26 awg copper in the cable. (some are even worse and are actually copper clad aluminum which is very very bad) Assuming you have 70 watt devices and you are using cat 5e 26awg cabling, you would be limited to no more then a 48 port patch panel because your bundle of cable would be too large otherwise. In a typical medium sized office space with 2 48 port patch panels a minimum requirement of cabling would Cat 6 with 23awg wiring.


There are of course many more factors involved. Also, one should consider not just what is required at the point of installation, but what would be required if the devices on the network were later upgraded to poe++ devices.


Consider too what could happen with some AHJ (local inspectors). It is possible that in order to be safe, he may conclude that he simply can not verify what type of device will be plugged in down the line, therefore he may simple require you to assume in your cable selection that you have the most powerful device on each line, thereby requiring the LP rated cabling, or Cat 6 23awg cabling in smaller then 48 bundles.


Making the wrong choice of cabling could cost you in the long run if it were to catch your building on fire, or if it simply prevented your construction project from passing the electrical inspection.


We hope this information has helped you ask the right questions of your cabling vendor. At Nashua Data Solutions we have always looked out for NEC requirements, and we are committed to do so for you and your companies needs in the future.


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