Power over Ethernet (PoE) basics and beyond

PoE is a godsend that should really be in more consumer devices and households, alongside structured wiring. An AppleTV, Chromecast, or NVIDIA Shield can easily fit within the envelope of PoE+, as can many enterprise-grade switches and WAPs (see UniFi as an example). Converting AC to DC once at the switch is more efficient (in resources and often, but not always, power) than including bulky PSUs for every device, while simplifying the ease of setup for end users (in theory).

Whenever possible, I opt for PoE. It’s a damn shame it’s limited to a niche userbase given its myriad advantages.

In my head enterprise grade switch has 48 ports with some >10g SFPs for uplink. What does enterprise grade mean to you? And what enterprise grade switches are poe powered?

Probably USB-C wall outlets will end up solving this instead.

Might be because it's scary. User plugs passive poe into something not expecting it, magic smoke

Arista 710P for instance. I don’t see what port count has to do with it, it runs the same OS and has the same capabilities as all their other switches. Cisco has a Catalyst 9k like this too.

Passive PoE is evil, standard PoE is safe since does negotiation.

Step 1 is to eradicate passive poe then

Passive PoE is already extremely rare today. Early Ubiquiti stuff probably is the most passive PoE stuff likely still in service.

Ubiquiti has stopped selling anything with passive 24V PoE, and has lots of standard PoE. The risk is low since I think only worked with injector so no switches providing power to everything.

It's such a wide field that it's hard to pin down. I agree if your thinking about what a business that isn't just a handful of people needs then we'd be looking at the kind of switch you're thinking of if it has standard office workers. But soon as you start talking about businesses that are manipulating central data (which keep in mind would probably include most primary business, design workers or anyone working with media not just software people) you're talking about a wide gamut of devices that you wouldn't really (at least traditionally) call consumer grade.

Mikrotik website has a good selection of them and if you look at the other hardware types it'll be interesting in getting an idea of weird things you don't see in normal offices.

https://mikrotik.com/products/group/switches

Apart from obviously larger bandwidth options like 28qfsp 100gb (I'm unaware if mikrotik does them but 400gb is normal in some circles) there's things like reverse POE switches, media converter switches, and all sfp+ switches.

Poe++ exists and you can use switches with it to power poe+ switches that will power poe switches. Or they can be used to power laptops or NUCS directly.

There are finally PoE adapters that give USB-C power and USB Ethernet. Those should allow home theater devices to be powered and use wired Ethernet. But the ones I have found are expensive, but should drop if there is demand.

> Converting AC to DC once at the switch is more efficient (in resources and often, but not always, power)

Can you expand on "often, but not always, power"? Here's my guess:

* It's more efficient for the small stuff: little wall warts aren't very efficient I think in part because there's some no-load consumption for each. The switch pays that no-load cost once for many devices and has like an 80-plus gold or better PSU, hopefully. And then I think even cheap buck converters are like 95% efficient; they have some no-load consumption too but I think less than the wall warts? And even though this goes over 2 (or 4) tiny wires, at 48V–56V, the current is low enough that power loss is not bad because those wires are just for one small device, and P=I^2R.

* It's less efficient for the big stuff: that P=I^2R starts to suck for the PoE case, and in the non-PoE case they're more likely to have efficient AC->DC conversion on their own. 90% efficient beats 90% * 95% efficient.

It’s supported by the latest revision of Glinet’s Comet kvm over IP hardware, which was a cool upgrade imho.

https://www.gl-inet.com/products/gl-rm1/

Which is ok if done right, but if they're anything like the usb-a ones there'll be plenty that are continuously pulling much more power than they need let alone the danger of uncertified ones.

For those thinking about adding one they've grabbed off amazon and installing themselves, please do a bit of hunting and reading rather than just buying the first word soup brand cheapest ones. Also remember installing uncertified electronics in your walls is a good way to void your insurance if they're the cause of disaster and turn it into a legal battle even if they're not.

Doesn't really make any sense to in that example.

Where ever you're putting the TV you have to put in regular power anyways, so it's fairly tidy to just put the device's power cable parallel with the TV's power cable. WiFi will handle communication. On the other hand, NEC and CEC requires minimum of 2 inches gap for communication wiring to electrical so you're now you've got that minor complication.

POE makes sense mostly when it makes sense to combine communication and power cabling. Corded phones, wifi access points, security cameras, small touch screen modules, etc. Not saying what you're doing can't work, but the added expense of installing parallel CAT6 everywhere doesn't seem worth it.

Besides being reversible, USB-C is a horrible connector. Tiny contacts, no positive retention, and a massively overengineered standard that should've been broken up.

In my head, one of the things that makes up an "enterprise grade" switch is 48 ports. Because "for the enterprise", in my opinion, evokes some idea of large scale deployment, not a mom and pop trinket store with one PoS cash register device and three company computers.

What does enterprise grade mean to you?

I already use splitters throughout my stack and devices, but that’s additional material and complexity cost compared to native PoE.

> An AppleTV, Chromecast, or NVIDIA Shield can easily fit within the envelope of PoE+

I ended up buying a PoE extractor and barrel plug adapter for my Roku, and another extractor for my HDHomeRun.

It annoyed the heck out of me that they had PoE running to them and still had to be plugged into a separate transformer.

> Ubiquiti has stopped selling anything with passive 24V PoE

In their consumer "UniFi" product line. Pull up their store and switch over to the "UISP" product line. Most of the smaller wireless devices and consumer-tier CPE are 24v passive, most of the larger wireless devices, 60GHz bridges, etc. are 48v passive, a few devices in the middle support both, and standard "active" PoE is almost nowhere to be found. Even on product lines that weren't even dreamed up when modern standard PoE was ubiquitous.

They say it's because the WISP crowd loves passive PoE as it can easily be wired to batteries on towers, and I get that, but that's no excuse for not also supporting standard-based PoE on the device end. There's no good reason for a product designed in the 2020s to force the installation of passive PoE where there was none prior.

They demonstrated they can do both with most of the transition-era UniFi products. Support and encourage the use of standards, allow the use of non-standard but common alternatives where they make sense.

Also my UniFi AP has passive poe cause it's just that old. Without researching, idk when that got fixed because nothing on the boxes tells you. Consumer tier means people will plug whatever fits.

The smaller switches like the Arista 710P are meant for deployment out at the edge of the network where you want something small and quiet (e.g. at people’s desks or in conference rooms) to provide more ports without needing as many runs back to the network core where the big loud switches live. They’re still enterpise grade since they support enterprise features like centralized management, VLANs, QoS, IGMP snooping, etc.

All our desk phones at work are poe and they have pass through ports to allow connecting a PC to the LAN. Really neat to just have one cable that gives you a powered phone, and Ethernet access.

Theory and practice and all that, but that shouldn’t happen regardless.

A correctly-designed Ethernet interface is galvanically isolated at both ends to avoid ground loops, differing grounds, and other nasties over long distances.

I also haven’t found any bidirectional ones yet, even though the hardware (except maybe the negotiation chip if it’s pure PDE) should be able to support it. Would be really nice for development of PoE devices to just hook up one dongle to my laptop.

So my arista 710p-16p isn’t entries because it’s not 48 ports? Or my Nexus 9300 24p? I’ve got some old juniper 4300 32F ports handling 1g fibres (moderns arista switches aren’t great as the 25g SFPs won’t autoneg at 1g on fibre as they don’t support clause 37)

My standard campus switches are 722s with 48 ports and 25/10 SFPs, but there are use cases when smaller switches make sense.

I have a mild obsession with the idea that there should be a PoE lighting standard. There is a two wire automotive ethernet standard that can deliver 50-100W. Which is enough to run a couple of LED or fluorescent lights.

A power supply can operate most efficiently if its power output is close to what it was designed to supply. Typically, a PoE switch has a large power budget to take into account the myriad devices that might be connected to it.

If you have one small PoE device connected to a large PoE switch then it would be less efficient compared to a non-PoE switch and a small separate power supply for the device.

I feel your pain. Prior to my network rebuild at home, I had splitters powering the EdgeRouter, Philips Hue Bridge v2, a Raspberry Pi, and was tempted to add more for the various small (<8-port) ethernet switches scattered about. UniFi expanding their switch lineup to include PoE-powered gigabit and 2.5G switches was a godsend, as were PoE HATs for the RPis’. Only the Hue Bridge remains on a splitter, because Signify won’t make one with native PoE.

I thought so as well when USB-C was first seeing widespread adoption, but now I’m not so sure. High-end PoE deployments can reach 90W of power down the line, and even HDBASE-T can support 100W of power down the line. Combined with the 8P8C connector both use (which is easy to field repair or replace and has positive retention), and I’d much rather see more structured ethernet runs and outlets with PoE/HDBASE-T for all but the most demanding or performant kit.

I don’t follow. What part of this would a USB-C wall outlet solve? This would just be swapping a 120/240v cable for a USB cable, right? PoE reduces the number of cables, among other advantages.

My Chromecast uses USB C for its network. I got a power brick (official Chromecast) that also takes an ethernet cable and then provides a wired ethernet connection.

That being said, a quick Google search for "poe usbc" yields some devices that are much more expensive than the power brick I bought, but in theory would let you run a Chromecast from a poe ethernet port with wired ethernet.

I remember when USB first came out and there was a ton of novelty in powering all sorts of random stuff out of your computer’s USB port like fans and mug warmers. This has me wondering what sort of whacky stuff I could do with a PoE extractor/splitter. An ethernet desk lamp would be fun. I have 24 PoE ports on my switch and I’m only using three of them for PoE. Time to get creative.

>> I like pancakes.

> Oh, so you hate waffles?

Hell, the switches we’re talking about support OSPF, BGP, VXLAN, the works. THAT is enterprise to me.

They have shorter operational life than most computer keyboards.

I agree sentimentally but apparently it's not considered the brightest idea to run data and real amounts of power together. I think that's why PoE is always treated like alcoholic beverages.

Normal people use WiFi not Ethernet so they only need a power cable. If the outlet provides USB-C it eliminates the need for wall warts.

> Without researching, idk when that got fixed because nothing on the boxes tells you.

In fact it did, in the transitional models that were sold both with and without 802.3af support there was a sticker added to the box on the ones that had it.

The switch was early in the life of the UAP-AC series of access points. IIRC the "Pro" and in-wall models always supported 802.3af but the "Lite" and "LR" models initially were 24v passive only. I vaguely recall there also being transitional models of their cameras but we were not deploying those at the time.

> Consumer tier means people will plug whatever fits.

And this is why I hate passive PoE with a passion. Standards-based PoE ports are safe, you can plug devices not supporting PoE (or requiring passive PoE) in to them with no risk of damage. Passive PoE ports are dangerous, they can and will destroy things that are not expecting to receive power on those ports.

They're even dangerous to devices designed for it in some cases, Ubiquiti actually famously had problems with UAPs on the end of long cables being damaged when fed by passive PoE from the source and eventually recommended that those installs add their "Instant 802.3af" adapters which took standard 802.3af over the wire and converted it to passive right at the device end. I had one site that lost three UAP-LRs before that was revealed.

If you're plugging in anyways why not make it ethernet though? Then you actually get multiple benefits (faster more reliable networking, freeing up wifi capacity for devices that actually need it) rather than just changing one cable for another.

I realize that for whatever unknown reason there are a subset of people who think everything should be wireless, but those people are wrong and should not be listened to.

> I have a mild obsession with the idea that there should be a PoE lighting standard.

Ubiquiti did this for a while, the product line was called UniFi LED and IIRC it didn't get much further than a few panel lights intended for drop ceilings and a wall mount dimmer switch.

IIRC the justification was that because it was low voltage it could be installed by anyone instead of potentially requiring an electrician and you then also got the ability to dynamically adjust grouping, switch behaviors, etc. if for example your floorplan changed.

I bought last year a device like that I think - was from some company named TexasPoE I think, and it took Ethernet cable, and output has usb-c with 1GbE and power. I sometimes use it with my iphone or iPad and do get the wired Ethernet connection and charging

My entire basement is currently lit by Poe++. Poe ethernet cable to metal utility box. Metal utility box contains Poe++ to 12v adapter. 12v adapter output wires screwed into utility light socket base. 12v led lightbulb screwed in to led lightbulb socket.