Power over Ethernet (PoE) Installation Best Practices

One of my favorite sayings regarding the technicalities of Ethernet cable installations is “usually, but not always”. What I mean is that the answers are often not concrete and vary by your installation and your goals. There can be more than one correct answer. Some answers are more correct than others.

Interestingly, within a certain boundary of guidelines, the issue of Ethernet cable type has more to do with the specific installations than the actual Category or construction of the cable.

Here are some more concrete generalizations:

• Any Category of Ethernet cable from Cat5e upwards is capable of carrying IEEE Type 4 Class 8 PoE (802.3bt, and referred to as PoE++) up to 100W as long as the construction is of copper (stranded or solid)
• As you increase the number of PoE cables in a bundle the number of cables must be reduced and is relative to copper AWG size and Category
• As you increase the current (PoE Class/Type) the number of cables in a bundle must also decrease relative to copper AWG size and Category
• It is better to not construct larger bundles of Ethernet cables carrying power, as air circulation around the cable for heat dissipation is your friend
• Ethernet cable bundles carrying PoE that are put inside conduit are even more limited as to cable count, so avoid conduit if you can but there are guidelines found below if you intend to use it

So, the “usually, but not always” mantra rears its head here if you want to find out the specific number of cables you can get away with. That is the reason I kept putting key items into italics. The answer is: It depends. More on that later.

Termination Accessories

As for termination accessories, all of trueCABLE’s Ethernet keystone jacks, field termination plugs, Ethernet couplers, and RJ45 8P8C connectors handle Type 4 Class 8 IEEE 802.3bt, PoE++ up to 100W with no issue. As it turns out, the limiting factor on PoE ratings for accessories has to do with a phenomenon known as “spark arc damage”. This happens by plugging and unplugging live PoE circuits.

Before and after results of unplugging a live PoE circuit.  This damage does accumulate!

Each time you plug and unplug a live PoE connection, a tiny spark is created. Over time it will accumulate in the form of minute pitting and burns on the surfaces of RJ45 8P8C contact wires and the associated contact springs inside keystone jacks or couplers. Accumulation of this (not always visible) damage will contribute to performance degradation and possible termination hardware damage. Note, we are not talking about a few plugs and unplugs. We are talking about hundreds. In other words, this is not a huge worry but we will address that later too as the problem can be avoided.

Table:  Maximum PoE Cable Bundle Size with Multiple Variables

 

* Type 3 and Type 4 are also known as 4PPoE or 4 Pair PoE. Type 2 PoE is 2 Pair PoE.

Notes for using this table:

• If using shielded Ethernet (F/UTP foil overall shield) then the cable counts above may be safely increased by 10% as the shielding allows for better heat dissipation
• Bundles of mixed Category cables carrying PoE should be rated with the worst case scenario in mind (for example, if you have Cat5e and Cat6 in the same cable bundle then use the figures for Cat5e)
• Cat5e conductor gauge is assumed to be 24 AWG
• Cat6 and Cat6A conductor gauge is assumed to be 23 AWG
• All figures are for solid copper conductors
• Ambient temperature is assumed to not exceed 113℉ or 45℃
• This table is constructed to avoid a temperature rise exceeding 27℉ or 15℃ above ambient so as to not exceed the cable operating temperature

Here’s a pro tip (and shortcut!). If you base all of your maximum run lengths off of the guidelines found in Temperature's Effect on Ethernet Cable Length and then secondarily use the table above for bundle sizes you are good to go for the worst case scenario!  

WAIT, THERE’S MORE! If you base your bundle size and run lengths using the above tip and then combine that with Conduit Fill Chart for Ethernet and Coaxial Cable for installations requiring conduit, you get a FREE set of steak knives! Well, not really, but you will be operating like a master chef. Proper Ethernet cable installations are a balancing act of multiple factors taken into account.

Do’s and Don'ts for PoE

Do:

• Opt for higher Category cable (which will typically have thicker copper conductors) when feasible for PoE applications
• Opt for F/UTP (shielded) Ethernet cable when working with large numbers or very high wattage PoE runs (or both) especially if bundled
• Avoid bundling when possible, but follow the table guidelines above if you cannot
• Use velcro cable straps to bundle cables if bundles are necessary
• Avoid conduit and similar pathways if possible, otherwise defer to ENT or similar metallic conduit for better heat dissipation and follow the table guidelines above if you cannot. Metallic conduit should be properly bonded and grounded to AC ground for safety.
• If bundling cannot be avoided, follow the table guidelines above and also cross reference with Conduit Fill Chart for Ethernet and Coaxial Cable
• Keep bundles separate by at least 1.5” in cable tray to allow for air movement
• Power down PoE ports prior to plugging or unplugging end equipment or working on the cable

 Do NOT:

• Use CCA or copper clad aluminum conductor Ethernet cable (ever)
• Use zip ties to secure Ethernet cable. Cable damage over time will occur which will degrade performance, and cables cannot dissipate heat nearly as well.
• Put 26 AWG or 28 AWG stranded copper Ethernet cable into conduit when it is running PoE. Open air bundles are OK, but that will be addressed in another blog.
• Comb out cable bundles for perfect alignment and visual appeal. Although this is a trend as of late, it turns out that cable combing for visual appearance will not only cause potential immediate alien crosstalk (ANEXT) between cables but also long term cable damage due to bundle sag and lay. Lastly, perfectly combed out cable bundles also do not dissipate heat generated by PoE as well as randomized bundles.
• Use any of the advice in this blog if your PoE application type is manufacturer specific (proprietary). Defer to that manufacturer’s advice for cable installation considerations. This blog assumes IEEE 802.3 style PoE is in use, which is industry standard.
• Repeatedly plug or unplug RJ45 8P8C connectors or field termination plugs from female mating interfaces when the PoE circuits are energized as accumulated damage will result and may degrade performance over time or even damage end point devices

PoE Quick Rule of Thumb

As luck would have it, the vast majority of Ethernet switches and patch panels come in rows of 24. Although you may be dealing with a 48 port PoE switch or 48 port patch panel, it will be two rows of 24. Well, it turns out that 24 is below the absolute worst case scenario of 31 Cat5e cables bundled into a conduit when running at 100W on 802.3bt PoE++.

Simply keep any bundle to 24 or less and then keep those bundles separated by 1.5” and at no point will you ever run into a problem. For commercial installations, the side benefit is any code inspector coming out to inspect your work will have a much easier time figuring out what you have done and you will be able to pass code inspection easily--and that will save you time and hassle. Yes, the NEC does indeed address PoE now, therefore your inspector can hold you to it. Avoid trouble and lots of extra explanations with this strategy!

And there you have it. The average DIY installer and/or homeowner is not likely to bump into the maximum worst case scenarios outlined in this blog, but PoE is becoming more and more important to IoT and smart devices designed to save energy and provide convenience. It is best practice to follow these guidelines for any installation as you never know what the future will bring. With that I will say…

HAPPY NETWORKING!