Fundamentals of Power over Ethernet

Whether You’re New to PoE or Just Want a Better Understanding, We Explain Will PoE

I’ll start by saying that I love Power Over Ethernet (PoE). 

Yeah, yeah, it’s what we do for a living, but, really, how cool is it that you can take the ethernet cable you have in your wall and get it to power up lights, cameras, iPads, or even TV’s?  I see PoE as Potential (okay, yeah, I couldn’t resist the nerd joke, and be forewarned they keep coming).

In all seriousness, though, Power Over Ethernet can save you 30% on any given project where you would otherwise have to call a licensed electrician to pull a permit just to put an outlet somewhere so you can hang a camera.  Even better, because PoE runs on low voltage power (less than 56 volts) you can safely do the work yourself, or at least get your techie nephew to do it.

If it’s so cool, why doesn’t everyone do this all the time?  Frankly I’m stumped.  However, I blame it on it sounding too technical because it has to do with computers talking to each other.

That ends today. I help a lot of people find the right PoE solution, and believe me when I say you can understand PoE. Once you have a few basic terms and principles, you’ll blow minds! To make that magic happen for you I will simplify Power Over Ethernet (PoE) in an easy to understand way even if you’ve never worked on a network before.

Let’s start off with a pronunciation guide.  This is worth your time.  You drop this on your friends and coworkers, and you become the de facto expert on PoE. 

  • PoE – pronounced PEE – OH – EEE.  Not like Edgar Allan “Poe”.
  • IEEE 802.3af – pronounced EYE TRIPLE EEEE EIGHT OH TWO DOT THREE AYE EF.
  • Okay, so say it with me now . . .  EYE TRIPLE EEEE EIGHT OH TWO DOT THREE AYE EF.

Great work!!

So what does that all mean?  Working from the ground up (another engineer joke!), PoE means putting electricity onto an ethernet cable along with a data signal.  You can use that electricity to power all kinds of things: cameras, lights, wifi access points, iPads, phones, TV’s, computers, media players, Raspberry Pi’s.  Warning: once you get into what you can power with PoE, it goes deep, like X-Files deep.
Oh, about the IEEE thing (yeah, you heard how cool you sound saying it).  Simply put, you have a very smart guy making cameras and you have another smart guy like me – ahem, why thank you – making devices that can power those devices over a network cable.  To make sure we all work together without having to constantly fight over things, we called our friends at the Institute of Electrical and Electronics Engineers (IEEE – “EYE TRIPLE EEE”) and asked them to help us create a standard way of doing things.  They agreed and added us to the 802nd section part three subsection “af” of their standard.
You don’t need to read it, but if you do – SPOILER ALERT – data and power get together by the end.
That standard is how engineers agree how the PoE will work, so we both make devices that talk the same PoE.  As time passed we kept coming up with better and better ideas, like MORE POWER!  So now we have a few more standards.  Here’s a table of the PoE standards as they stand today (don’t worry, I will explain it all so just bask in the glory of it):
PoE Type or Standard Nickname Power Per Port
(at the device)		 Types of Devices
IEEE 802.3af PoE 12.9 watts
IP Cameras
IP phones
iPads and Tablets
(<10″)
IEEE 802.3at PoE+ 25.5 watts
Outdoor PTZ Cameras
Dual Radio Wifi Access Points
USB Type C phones and tablets
(>10″)
IEEE 802.3bt PoE++
4Pair PoE		 79 watts
Televisions
Lights
Blinds
Laptops
*Passive PoE 24 Volt PoE
Passive		 Up to 55 watts
Ubiquiti or Mikrotik
Wireless Internet PtP or PtMP
(big Wifi Radios)

*Passive PoE can operate anywhere from 12 volts up to 58 volts. You’ll want to check your specifications carefully to make sure they match your device.

Oh no!  My Lights or IoT Devices Don’t Have PoE!

Have no fear.  You can use a device called a PoE Splitter or Node to change PoE into almost any kind of power you need: USB, 12 volt DC, 19 volt DC, USB Type C.  So find out what kind of power you need, then get a splitter for it.
The real difference between the types of PoE is how much power your devices need called out in Watts.  What you need to know is that the watts are how much power a device consumes to do its job.  The last column shows you the kind of devices each power level can support.

 

And  that, my friends, is all you need to know.  Seriously.  When it’s all said and done, you just need to make sure you pick a Powered Device (PD) like a camera or media controller that matches the standard of the Power Sourcing Equipment (PSE).  You like how I snuck . . . sneeked . . . er . . . snooked some more vocabulary in there?

 

“But how do I do that?” you ask.  I’ll break it down bullet point style.  Let’s say you’re looking to add a new camera or any device to your network.
  • First, go find the datasheet.  Don’t Panic.  Every engineer makes a datasheet because its their way of bragging.  It’s like they’re street racers with their tricked-out muscle cars, they want you to know what they’ve got under the hood.  Typically, you can find PoE in the Electrical section.  You’ll find something like “POE” or “IEEE 802.3 af”.  That tells you what kind of PoE your new toy has.
  • Second, select a type of Power Sourcing Equipment (PoE), that’s your PoE switch or midspan (injector).  What’s a switch and what’s a midspan you ask?  They look a lot alike, but don’t be fooled.  They’re different animals with different purposes like a king snake and a coral snake (Krykie, she’s a beauty!  I’m going to pick her up!).

Why use a Midspan when I can just buy a PoE switch?

There are two situations where a midspan injector makes more sense:

 

1) Let’s say you have your network all set up, and it’s working great.  All the ports are forwarding, Quality of Service (QoS) is great, and everything has been working for a while.  If you’re like me, the guy who set up the network has gone all Jason Bourne on me which means I’ll never find him again.  Then you need to add PoE to it, or you need to add PoE+ to your PoE switch because you just need that little extra power.  Do I really want to try to pull out that switch that I paid a lot of money and headache to get configured to add a few PoE+ devices?  At this point, it’s not about the money, it’s about the headache of nothing working for a month while we get it all sorted out again.  Or do I just add a midspan in a few minutes and forget about it.

 

2) You don’t want to have to buy a switch that doesn’t have the features you want just because it can do the PoE you want.  We see this more often than you’d think.  For example, you have an NDI switch that doesn’t have PoE or doesn’t do PoE+.  You need that PoE power for your streaming camera.  Do you buy an NDI switch that may be way more than you need with PoE+ or just use a midspan to add it to the switch you know and love?
  • Finally, once you know your switch or midspan is compatible, then make sure you have enough ports and power budget for all your PoE devices on your PSE.   Most switches and some midspans don’t have enough total power budget to give you full PoE power on all ports at the same time.  Why?!  you may ask.  It comes down to cost and how much you’ll really use each port.  Your Toyota Corolla technically can go to 120 mph, but you really use it to get to work and back.  If you really wanted to go 120 mph, you upgrade a Porsche or Corvette or something truly awesome.   

There’s a catch . . . this part takes . . . gasp . . . math.  I know you swore you would never touch a calculator again when you got out of school.  Believe me.  It’s not that bad.

Simple Method:

Add up all the rated power consumption of all the devices and compare it to the rated power of your PSE.  For example:
2 x PTZ Optics cameras at 12 watts each = 24 watts
2 x Polycom Phones at 6 watts each = 12 watts
1 x High End Wifi Access Point (WAP) = 23 watts
All together: 24 + 12 + 23 = 59 watts

 

You need at least 5 ports and a total of 60 watts.  Oh, and by the way, you need PoE+ for that high end WAP.

Nerdy Method:

I couldn’t leave you with it that simple.  If you’d really like to get details, you can use our PoE Calculator to estimate how much you can expect in cable loss as well!

 

New now, you can find our APP for Apple and Android devices!

If you find yourself saying, I’m not going to remember all that!  Don’t.  Just remember to come back to your book here to find a link to a handy tool to walk you through your PSE selection process.  You can find it in our

PoE Specifier's Guide

Download our workbook to help you select the right Power Over Ethernet for your application.

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E voila!  That covered what you need to know.  You now know more than 90% of people in the world about Power Over Ethernet.  With this simple set of tools you’ll shock yourself (please only figuratively) with what you can accomplish and how easily it will happen.  Put that 30% into a new rocking set of drums or your kid’s college fund, whatever you think is most important.  Whether you decide to tackle a project yourself or hire someone else, you now have the core knowledge you need to handle a Power Over Ethernet project.

 

I will close with the immortal words of Stan Lee, “With great power comes great responsibility”.