PoE basics and beyond: What every engineer should know
25 comments
·October 16, 2025skopje
skulk
Got any recommendations on what cameras to get? The market is absolutely flooded with cheap shitty cloud-connected all-in-one cameras making it hard to find good, simple products.
lights0123
Any of those that mention ONVIF or RTSP will do if you put them on a LAN without internet access
stargrazer
reolink, also look at the frigate nvr software, they have a list for decent recommendations
zer00eyz
This is the way.
Reolink cameras are pretty good for what they are. Just dont buy into their NVR solution...
Frigate also has some interesting applications to go along with it, see: https://github.com/mmcc-xx/WhosAtMyFeeder
I also have YOLO on my to do list for the home cameras.
stego-tech
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.
wmf
Probably USB-C wall outlets will end up solving this instead.
dfc
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?
rmunn
Practical question for HN: How do you all label your PoE cables so that you don't accidentally plug the powered cable into a socket that wasn't expecting 48 volts on those pins and fry something? (I know the power injector is supposed to only deliver power when it's safe, but if all your devices work exactly as they should all the time, then I'd like to buy that bridge in Manhattan you're selling).
Do you buy Ethernet cables of different colors and say "Yellow is reserved for PoE, all yellow cables should be assumed to have power on them"? Or do you slap a "48V" label on both ends of the cables you're going to use for PoE and the label is what warns you that this cable should only go into the PoE receiver, and not into an unpowered device? Or do you just not label your PoE cables any differently, and trust that the injector will never malfunction at the same time that you plug the PoE cable into the wrong device?
Kirby64
Unless you’re using the “passive” PoE variants (ubiquiti sold these for awhile, for instance) that always has voltage on the pins, there is no risk. Negotiation is mandatory for the actual IEEE variants. Just use those and don’t worry about it.
supertrope
Always buy standards based equipment. 802.3af, 802.3at, 802.3bt. You can label cables and jacks with red lettering (“Passive PoE. will fry your laptop port. Really!”) but it only takes one mistake to let the magic smoke out.
VanTheBrand
I completely avoid passive PoE. Not worth the risk. On the standardized active stuff I’ve never had any issues even when I’ve plugged it broken cables to unpowered devices.
leoh
What every engineer really should know!
doubleg72
Well the entire point of standards is so things work exactly as they should every time. I haven’t seen any issues with standards based poe
leoh
I'm just, like, vibe-coding, man. Why do I need to know about PoE?
davydm
came for the poetry, left with an engineering lesson
cyberax
What about PoE for 10G Ethernet? I see that there are some vendors (e.g. Ubiquity) that are offering devices with it, but I don't see it in the standards?
zamadatix
I think every major vendor has had 10G PoE switches: Arista, Aruba/HPE/Juniper, Cisco, Extreme, and Fortinet for sure. The problem is there is little use case for 10G + PoE in the enterprise and even less for consumers. Ubiquity likes to tout it for the 10G APs... but, realistically, most are worried about airtime with APs, not 10G wired throughput from a single one when they have a thousand.
As a result, it tends to be relegated to the "high end switch which has every feature those one-off customers demand but costs an arm and a leg as a result" model/family. E.g. the only ones I ever sold were to a hospital that wanted to have select switches have 10G for radiology workstations but also wanted to still be able to plug 1G APs in without having to think about the port types. Radiology was covering the cost, so they didn't care it was a waste of money.
VanTheBrand
I find it useful in Broadcast Video Production (that’s where I end up using it most) and yeah with Wifi7 supporting > gigabit speeds I’ve seen some Wireless Access Points supporting it (though 2.5GbE Poe++ is more common there and practically speaking enough)
VanTheBrand
As of 802.3bt (PoE++) the standard includes support for “all standardized copper link speeds of up to 10GBASE-T.” The previous standard 802.3at (PoE+) added gigabit support.
So any 10GbE (and 2.5GbE) PoE/PoE+ devices out there are technically not to spec (lots of these on Ali Express) but I believe the the Ubiquiti 10GbE stuff is all at least PoE++. [1]
(They do have their own non spec labeled PoE+++ products though, which are really just “802.3bt Type 4” but they added another plus because that probably sounded better.) [2]
[1] https://store.ui.com/us/en/products/us-xg-6poe, https://store.ui.com/us/en/category/accessories-poe-power/co...
[2] https://store.ui.com/us/en/category/accessories-poe-power/co... , https://help.ui.com/hc/en-us/articles/115000263008-PoE-Avail...
brcmthrowaway
1. Why are IEC/Edison cables so thick if Ethernet can carry the equivalent power?
2. How does PoE compare to Powerline Networking?
skinner927
1. Assuming IEC refers to cables we plug a desktop PSU into mains/wall: IEC can carry up to 1800w vs 100w PoE++
2. Powerline networking is considerably slower and less reliable than CAT5/6. Additionally, building code for running power lines is much more strict than low voltage CAT5/6
otterley
No Ethernet cable that I’m aware of is capable of carrying anywhere near 15A of current. Even type 4 (90W assuming 57V) is 1.5A.
PoE is awesome. My custom home security system is all CCTV PoE with a gstreamer backend running on four-core fanless linux box. Way to go. Complete control. No batteries, no wares spying on me, no personal data getting scraped by big guys. (Cloud connectivity sucks because I have segmented mp4s and jogging through them hurts but I only care for events after they happen, not while they happen.)