10 ms·

Power over Ethernet (PoE) basics and beyond

262 points by voxadam 1y ago

cyberax 1y ago
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?
- VanTheBrand 1y ago
  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/products/us-xg-6poe, https://store.ui.com/us/en/category/accessories-poe-power/collections/pro-store-poe-and-power-adapters/products/uacc-poe-plus-plus-10g https://store.ui.com/us/en/category/accessories-poe-power/co... [2] https://store.ui.com/us/en/category/accessories-poe-power/collections/pro-store-poe-and-power-adapters/products/uacc-poe-10g?variant=uacc-poeplusplusplus-10g https://store.ui.com/us/en/category/accessories-poe-power/co... , https://help.ui.com/hc/en-us/articles/115000263008-PoE-Availability-and-Modes https://help.ui.com/hc/en-us/articles/115000263008-PoE-Avail...
- zamadatix 1y ago
  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 1y ago
    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)
- zer00eyz 1y ago
  My question is this: what would you plug into POE that would need 10gbe?
  - wmf 1y ago
    A multi-radio WiFi 8 AP?
    - zer00eyz 1y ago
      You would likely need fiber to saturate it...
  - mrheosuper 1y ago
    an all nand-flash NAS ?
  - fc417fc802 1y ago
    What if you need a small switch somewhere due to the runs otherwise being too long?
  - MBCook 1y ago
    I had no idea it could supply 90 watts or so. At that point you could power some pretty powerful terminals. The new 14” MacBook Pro comes with a 70 watt charger. An M4 Air only gets a 35 watt adapter. Basically seems like enough power is available to run something pretty powerful.
    - zamadatix 1y ago
      It's really ~71 watts on the device end (not counting any inefficiencies in the device itself). Still plenty powerful to do a lot with, but also more limiting. Especially if you don't already plan on having a built in battery to handle bursty workloads for whatever reason the device needed a 10G port for.
      - sodaclean 1y ago
        With most day to day things being some form of streaming it really hides how painfully slow gigabit is. Additionally, it's not difficult to fit 10gigabit worth of data munging in a 10-15watt envelope. Pulling data off of modern professional cameras is an easy example. Realtek's latest NIC is 10/100/1000/2.5/5/10, has a <2w envelope and has offloading that works (unlike intel).
- toast0 1y ago
  Should work just as well as PoE for 1G ethernet. All four pairs are active data, but you should be able to add a DC bias between pairs and tap it off the transformer on the other side, just like 1G
brcmthrowaway 1y ago
1. Why are IEC/Edison cables so thick if Ethernet can carry the equivalent power? 2. How does PoE compare to Powerline Networking?
- otterley 1y ago
  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.
  - gwbas1c 1y ago
    And don't forget that, with ethernet, every device needs its own run of cable, its own port at the router, ect, ect. Normal power cables support multiple devices.
- skinner927 1y ago
  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
  - dlgeek 1y ago
    Nerdsniped: You're describing a IEC 60320 C13 cable - they're technically only spec'd for 10A, which means you're looking at ~1200W, not 1800. (However, UL will list them for the full 15A -> 1800W, and I'm sure plenty carry that. And for that matter, I suppose you can get twice that in Europe on 240v...)
skopje 1y ago
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.)
- skulk 1y ago
  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.
  - stargrazer 1y ago
    reolink, also look at the frigate nvr software, they have a list for decent recommendations
    - zer00eyz 1y ago
      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 https://github.com/mmcc-xx/WhosAtMyFeeder I also have YOLO on my to do list for the home cameras.
      - mkl 1y ago
        What's wrong with their NVRs? I have one connected to some Reolink cameras (though not yet the full house-surrounding setup I have planned) and it seems fine so far.
    - aivisol 1y ago
      Reolink with Synology NAS using their native Surveillance app. All stored locally, no cloud. One issue with Reolink I haven’t solved is that it is unable to detect approaching cars in the night. Departing cars work fine though. Otherwise no complaints.
rmunn 1y ago
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?
- leoh 1y ago
  What every engineer really should know!
- supertrope 1y ago
  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 1y ago
  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.
- Kirby64 1y ago
  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.
  - sodaclean 1y ago
stego-tech 1y ago
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.
- dfc 1y ago
  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?
  - hackmiester 1y ago
    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.
    - dfc 1y ago
      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?
      - kevvok 1y ago
        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.
mmaunder 1y ago
Jeez top post on HN and there's a full overlay ad to "download a mac extension". This deserves a summary post to save others the click. Here's the "what every engineer should know" without the spam: PoE (Power over Ethernet) sends both DC power and data through the same twisted-pair Ethernet cable, allowing devices like IP cameras, wireless access points, and VoIP phones to run without separate power lines. The power is delivered by Power Sourcing Equipment (PSE) — either an endspan (built-in PoE switch) or a midspan (PoE injector placed between a non-PoE switch and the device). The powered device (PD) negotiates power via detection and classification before voltage is applied, preventing damage to non-PoE gear. IEEE 802.3af (Type 1) provides up to 15.4 W at the source, 802.3at/PoE+ (Type 2) up to 25.5 W delivered, and 802.3bt (Type 3/4) extends that to roughly 60–90 W using all four wire pairs. Engineers need to understand not just wiring, but also cable category limits, pair usage, power losses over distance, and heat dissipation — especially at higher power levels. Modern PoE designs must consider standards compliance, thermal management, and efficiency, as power density rises with new generations of PoE technology.
- pwg 1y ago
  With UblockOrigin in default deny all javascript mode there was no overlay ad.
  - IncreasePosts 1y ago
    Running a browser with javascript disabled is great, I recommend it to everyone. More often than not, you get a better experience - more responsive, your battery lasts longer, fewer ads. And, if the site breaks for some reason, you just allow list the site and reload.
willis936 1y ago
Other stuff engineers should know: - PoE endpoints should have isolation barriers, factor this into cost and size estimates - Don't skimp on TVS - ideal diode full bridge rectifiers are really cool and you should use them (in more power entries than just PoE)
- dynode 1y ago
  Awesome I’m just doing a POE design now. - Was having a conversation today about isolation and grounding for POE (product has a metal case). Do you have a reference? Or standard? - TVS ahead of the bridge right? - Do you have a part recommendation or reference design for ideal diode POE?
  - eqvinox 1y ago
    > - Was having a conversation today about isolation and grounding for POE (product has a metal case). Do you have a reference? Or standard? Huh. I'm not the GP poster but interesting question. AFAIK there is no proper ground reference on the LAN cable. I'm not sure I've ever seen a metal case… wait, I do, outdoor wifi APs have metal cases sometimes. If you find out, report back ;D > - Do you have a part recommendation or reference design for ideal diode POE? I've done a PoE device (802.3at, 25W) and just went with TI's reference design; the higher power ones use ideal diodes, sometimes there's multiple circuit variants. (It's not worth mucking with the PoE design for small-scale builds; the reference design might be a bit more expensive but you get that money back on way less trouble to deal with.)
  - willis936 1y ago
    The chassis net should be passed through the cable shield and the power isolated to force the current return through the cable in case power ground is bonded to chassis (which is commonly done, not sure why, I prefer a 1MOhm standoff). While not perfect this link is concise and provides handles to the relevant specs. https://www.brainboxes.com/faq/power-isolation-in-poe-ethernet-switches https://www.brainboxes.com/faq/power-isolation-in-poe-ethern... Yeah, TVS before any other silicon junction. It's nice to throw a single-use medium or slow blow SM fuse before the TVS to open circuit in device faults. This is going to be individual preference. I like the density and low design risk of fully integrated solutions like Microchip's PD70224. As long as you spec your FETs appropriately you can't go wrong with TI or AD options (VDS of at least 100 V, ID of at least as much current as you want to cram through with healthy headroom, RDSon that makes you happy, VGS that's compatible with the datasheet charge pump, size and cost that doesn't make you weep). When in doubt, stay very close to the datasheet's design. I just saw that the PD70224 is not recommended for new designs. What an awful day to have eyes. Oh, it's been superseded by the PD70288. Much lower RDSon, but a huge 8x8 package. The charge pump is mysteriously gone and there is now a UVLO of 24V. This is more PoE-specific, which is less generally interesting to me. If only someone would sell me an ideal diode full bridge rectifier IC with integrated FETs, OCP circuit breaking, UVLO, OVLO, a fault flag, control input, and current monitor, I'd never buy a different power entry IC.
Animats 1y ago
Not clear on how multiple sources on the same cable work. Is that allowed? Is there a power break at midspan, or does power flow through? How are the regulators coordinated?
- eqvinox 1y ago
  There are never multiple sources; a midspan PoE injector breaks the power flow and injects only its own power supply. It's done through the center tap on the Ethernet transformers. Midspans have another set of those transformers and inject the power on the PoE PD facing side. Whole pair(s) carry common-mode DC current, so basically your green pair could be ±48V and the orange pair 0V. If any, the upstream switch's injected power would just end at the other coil of the Ethernet transformer in the midspan. However, the midspan also doesn't pass through PoE negotiation, so the switch won't turn on power to begin with.
RandomBacon 1y ago
Question for anyone who might have a suggestion: I have a Ring home security system. I would like to get an offline home CCTV that only records when the alarm is set (either in Home or Away). A quick internet search does not show an API. I'm not sure Ring has a device that I could wire a relay (if that's the right thing) to.
dang 1y ago
[stub for offtopicness]
- davydm 1y ago
  came for the poetry, left with an engineering lesson
- leoh 1y ago
  I'm just, like, vibe-coding, man. Why do I need to know about PoE?
- scuff3d 1y ago
  Not gonna lie, I'm kind of disappointed this isn't a Path of Exile tutorial for engineers.
- elromulous 1y ago
  "every engineer"? Should a chemical or nuclear energy engineer have to know about PoE?
  - ThrowawayTestr 1y ago
    Sure. It's really useful if you're setting up a home security network.
- JoshGG 1y ago
  POE. Purity Of Essence ?
- varenc 1y ago
  you're a hero
sema4hacker 1y ago
POE switches can have more jacks than they can provide power for. I have five pan-tilt-zoom (PTZ) cameras but learned they can need up to 40 watts each, preventing plugging them all into a particular POE switch I had. Chaining a couple of switches solved the problem, be beware how much power your devices need to consume.
- ifwinterco 1y ago
  Is it actually likely that all 5 would be drawing full power at once though? It's normal in household wiring (at least here in the uk) for circuits to be somewhat undersized based on the concept of "diversity" (i.e. it's highly unlikely every socket on the circuit will be drawing 13A simultaneously)
  - publicmail 1y ago
    I would expect power consumption to be fairly consistent for something like a surveillance camera that emits a stream 24/7.
    - bombcar 1y ago
      Not if they’re PTZ; they’d obviously be drawing more power when panning, tilting, and (maybe) zooming if that is mechanical.
- Underphil 1y ago
  This is true of any electrical system, no?
ww520 1y ago
It is also good on delivering power to AES50 snake stage box to microphones that needs fathom power.
red369 1y ago
I recently needed to buy a new power supply for my Mikrotik router (hAP ac²), so I decided to just buy a Ubiquiti PoE injector instead. It feels magical to have the PoE injector tucked in a cupboard with the optical network terminal, and outside Narnia, the router has only one cable going to it. Also, the Ubiquiti PoE injectors are particularly satisfying. Powered by standard AC cables, and a nice simple design. Now that I've experienced this magic, I'm not going back! However, as much as I love the hAP ac², it only accepts passive PoE. I don't love passive PoE - it scares me! Unfortunately, it seems like most (all?) Mikrotik routers only accept passive PoE. Does anyone know of a good alternative when it comes time to replace my router? I would have liked it to be Ubiquiti, but I don't usually read positive things about them around here.
- bombcar 1y ago
  You can get the inverse of an injector that takes active PoE and makes a barrel plug out of it.
  - red369 1y ago
    Thanks for reminding me of that! I considered that when I was finding it hard to find a passive PoE injector. It's not quite as tidy, for example, with the router sitting visibly on a desk, but it's close. And you're right that it could work for anything.
    - sodaclean 1y ago
      I converted my Hue Hub to PoE with a splitter. It's super convenient but not the prettiest.
- nucleardog 1y ago
  > It feels magical to have the PoE injector tucked in a cupboard with the optical network terminal, and outside Narnia, the router has only one cable going to it. Last time I remember feeling like that was the day I unplugged a RB5009 and it... just kept running. Was standing there holding the power cable in my hand, clearly unplugged, and the router was sitting there still happily blinking away. Like, this clearly can't be possible but I'm staring right at it and it's happening. Took me a minute, but eventually realized the Starlink box that provides power to the dish _also_ provides power on the local side for their provided router as well, and apparently it was happily powering mine now.
mns 1y ago
PoE actually saved me, or at least helped me simplify some things. My router is in one place, while the distribution box where all the cable conduits lead to every room in another place. The distribution box (where also the optical cable originally comes from to the router) has no power plugs. I wanted to have Ethernet plugs in every room (especially for any fixed devices), so I managed to find (quite difficult in Germany) a PoE powered switch for the distribution box with no plugs available, get a PoE injector to power it and from there on to wire and install Ethernet plugs in all rooms.
le-mark 1y ago
Can anyone comment on what VEX robotics kits do with POE? Their controller box connects to motors via cat5 (they call them “smart cables”)which carry’s power, pwm, and encoder data. I don’t think it’s carrying ethernet but could be? Any sources for more info would be appreciated!
- lawik 1y ago
  It seems to be RJ11 and they might be spec:ed slightly differently (thicker leads?) to power motors. I get the impression it is mainly to control what can be used in competitions. This was what I found from skimming around: https://www.robotevents.com/V5RC/2018-2019/QA/35 https://www.robotevents.com/V5RC/2018-2019/QA/35 I doubt it is Ethernet at all, so it wouldn't be Power-over-Ethernet. Just some useful connectors and wires making for an appropriate cable. Also seems like you can make your own perfectly fine. Or they might melt. I suppose try it.
zara762 1y ago
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deleted 1y ago
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gwbas1c 1y ago
Is POE really relevant in the consumer space? All of my laptops get power and wired data through their USB C port. Does it make more sense to just send data over USB C? For example, my Chromecast gets power and wired ethernet through its USB C port. (I have an official Chromecast power brick that I plug an ethernet port into.)
- qwertyuiop_ 1y ago
  You wouldn’t have to worry about POE in the device category you mentioned.
sota_pop 1y ago
As an EE, once upon a time had a rep pitch PoE lighting fixtures. Cool idea, like allowing each individual fixture to be addressable/ controllable on a BAS, but they just had too many gotchas like coupling lighting (and by extension life-safety systems) to the server/network, additional voltage drop considerations, etc. Otherwise and for network gear, I really like PoE!
qaz147 1y ago
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qaz147 1y ago
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viggity 1y ago
I worked for a PoE lighting company for a couple of years. Yes, the ability to program your lights based on time of day, occupancy sensors etc was all nice for the end consumers. But the big advantage was that since it didn't use mains power, the owner of the building didn't have to hire a union electrician at eleventy gillion an hour to move some light panels around in a drop ceiling.
parliament32 1y ago
Something I've never understood: > The above figure shows a PoE injector with auto negotiation, a safety and compatibility feature that ensures power is delivered only when the connected device can accept it. Before supplying power, the injector initiates a handshake with the PD to detect its PoE capability and determine the appropriate power level. If PoE requires negotiation, and the device requires PoE for power.. how does it perform the handshake without being powered/booted first?
- _flux 1y ago
  Presumably lower voltage/current is provided first?
bokohut 1y ago
Quite the mix of comments in 2025 from something that has existed and been foundationally critical in many unseen systems. I designed and built my first POE system in 2004, at my own house as a dogfooding POC, and that system stills works to this day. Since that time I have built and installed many more without issue that continue to move along doing what they were intended to do, protect life and property via recording activity privately. My own home footage has been called upon several times by law enforcement and was critical in convicting at least one home break in crew. The benefit of install is simple to comprehend for those with significant experience in the electrical field, run one small wire for data and power and ensure the POE supply is on a battery - done. Additionally I add those using WiFi for security are laughed at daily as losses pile up, web search MLB player home break-ins, as running a hardline cannot be jammed but many foolishly put all their assets solely behind WiFi security. Also these surveillance systems require no external cloud by design so no one is watching remotely, unlike the Fed and State viewing your Ring cameras for years and now which recently partnered with Flocker. No one cares more about you than you so if someone is selling you security ask yourself what it is you are actually paying for. In closing, as we move into a new era of technological efficiency forced by rising energy prices and costly electrician labor hours, one is going to witness an uptake of POE adoption in more and more nontraditional places. It is already happening and its moment will come as more recognize the cost benefit to this greatly simplified power delivery method with integrated battery backup. What you cannot see matters most!
outofmyshed 1y ago
Passive PoE getting a lot of stick in the comments, but for one-off point solutions, it’s fine as long as you know what you’re doing. I have it to run a couple of MikroTik devices in awkward places and not having to run wall warts and flimsy DC cables around the place is very handy. My next switch upgrade will be a proper PoE+ one, but it’s not justified yet.

262 points by voxadam 1y ago

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?

VanTheBrand 1y ago
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/products/us-xg-6poe, https://store.ui.com/us/en/category/accessories-poe-power/collections/pro-store-poe-and-power-adapters/products/uacc-poe-plus-plus-10g https://store.ui.com/us/en/category/accessories-poe-power/co... [2] https://store.ui.com/us/en/category/accessories-poe-power/collections/pro-store-poe-and-power-adapters/products/uacc-poe-10g?variant=uacc-poeplusplusplus-10g https://store.ui.com/us/en/category/accessories-poe-power/co... , https://help.ui.com/hc/en-us/articles/115000263008-PoE-Availability-and-Modes https://help.ui.com/hc/en-us/articles/115000263008-PoE-Avail...
zamadatix 1y ago
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 1y ago
  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)
zer00eyz 1y ago
My question is this: what would you plug into POE that would need 10gbe?
- wmf 1y ago
  A multi-radio WiFi 8 AP?
  - zer00eyz 1y ago
    You would likely need fiber to saturate it...
- mrheosuper 1y ago
  an all nand-flash NAS ?
- fc417fc802 1y ago
  What if you need a small switch somewhere due to the runs otherwise being too long?
- MBCook 1y ago
  I had no idea it could supply 90 watts or so. At that point you could power some pretty powerful terminals. The new 14” MacBook Pro comes with a 70 watt charger. An M4 Air only gets a 35 watt adapter. Basically seems like enough power is available to run something pretty powerful.
  - zamadatix 1y ago
    It's really ~71 watts on the device end (not counting any inefficiencies in the device itself). Still plenty powerful to do a lot with, but also more limiting. Especially if you don't already plan on having a built in battery to handle bursty workloads for whatever reason the device needed a 10G port for.
    - sodaclean 1y ago
      With most day to day things being some form of streaming it really hides how painfully slow gigabit is. Additionally, it's not difficult to fit 10gigabit worth of data munging in a 10-15watt envelope. Pulling data off of modern professional cameras is an easy example. Realtek's latest NIC is 10/100/1000/2.5/5/10, has a <2w envelope and has offloading that works (unlike intel).
toast0 1y ago
Should work just as well as PoE for 1G ethernet. All four pairs are active data, but you should be able to add a DC bias between pairs and tap it off the transformer on the other side, just like 1G

brcmthrowaway 1y ago

1. Why are IEC/Edison cables so thick if Ethernet can carry the equivalent power? 2. How does PoE compare to Powerline Networking?

otterley 1y ago
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.
- gwbas1c 1y ago
  And don't forget that, with ethernet, every device needs its own run of cable, its own port at the router, ect, ect. Normal power cables support multiple devices.
skinner927 1y ago
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
- dlgeek 1y ago
  Nerdsniped: You're describing a IEC 60320 C13 cable - they're technically only spec'd for 10A, which means you're looking at ~1200W, not 1800. (However, UL will list them for the full 15A -> 1800W, and I'm sure plenty carry that. And for that matter, I suppose you can get twice that in Europe on 240v...)

skopje 1y ago

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.)

skulk 1y ago
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.
- stargrazer 1y ago
  reolink, also look at the frigate nvr software, they have a list for decent recommendations
  - zer00eyz 1y ago
    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 https://github.com/mmcc-xx/WhosAtMyFeeder I also have YOLO on my to do list for the home cameras.
    - mkl 1y ago
      What's wrong with their NVRs? I have one connected to some Reolink cameras (though not yet the full house-surrounding setup I have planned) and it seems fine so far.
  - aivisol 1y ago
    Reolink with Synology NAS using their native Surveillance app. All stored locally, no cloud. One issue with Reolink I haven’t solved is that it is unable to detect approaching cars in the night. Departing cars work fine though. Otherwise no complaints.

rmunn 1y ago

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?

leoh 1y ago
What every engineer really should know!
supertrope 1y ago
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 1y ago
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.
Kirby64 1y ago
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.
- sodaclean 1y ago

stego-tech 1y ago

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.

dfc 1y ago
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?
- hackmiester 1y ago
  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.
  - dfc 1y ago
    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?
    - kevvok 1y ago
      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.

mmaunder 1y ago

Jeez top post on HN and there's a full overlay ad to "download a mac extension". This deserves a summary post to save others the click. Here's the "what every engineer should know" without the spam: PoE (Power over Ethernet) sends both DC power and data through the same twisted-pair Ethernet cable, allowing devices like IP cameras, wireless access points, and VoIP phones to run without separate power lines. The power is delivered by Power Sourcing Equipment (PSE) — either an endspan (built-in PoE switch) or a midspan (PoE injector placed between a non-PoE switch and the device). The powered device (PD) negotiates power via detection and classification before voltage is applied, preventing damage to non-PoE gear. IEEE 802.3af (Type 1) provides up to 15.4 W at the source, 802.3at/PoE+ (Type 2) up to 25.5 W delivered, and 802.3bt (Type 3/4) extends that to roughly 60–90 W using all four wire pairs. Engineers need to understand not just wiring, but also cable category limits, pair usage, power losses over distance, and heat dissipation — especially at higher power levels. Modern PoE designs must consider standards compliance, thermal management, and efficiency, as power density rises with new generations of PoE technology.

pwg 1y ago
With UblockOrigin in default deny all javascript mode there was no overlay ad.
- IncreasePosts 1y ago
  Running a browser with javascript disabled is great, I recommend it to everyone. More often than not, you get a better experience - more responsive, your battery lasts longer, fewer ads. And, if the site breaks for some reason, you just allow list the site and reload.

willis936 1y ago

Other stuff engineers should know: - PoE endpoints should have isolation barriers, factor this into cost and size estimates - Don't skimp on TVS - ideal diode full bridge rectifiers are really cool and you should use them (in more power entries than just PoE)

dynode 1y ago
Awesome I’m just doing a POE design now. - Was having a conversation today about isolation and grounding for POE (product has a metal case). Do you have a reference? Or standard? - TVS ahead of the bridge right? - Do you have a part recommendation or reference design for ideal diode POE?
- eqvinox 1y ago
  > - Was having a conversation today about isolation and grounding for POE (product has a metal case). Do you have a reference? Or standard? Huh. I'm not the GP poster but interesting question. AFAIK there is no proper ground reference on the LAN cable. I'm not sure I've ever seen a metal case… wait, I do, outdoor wifi APs have metal cases sometimes. If you find out, report back ;D > - Do you have a part recommendation or reference design for ideal diode POE? I've done a PoE device (802.3at, 25W) and just went with TI's reference design; the higher power ones use ideal diodes, sometimes there's multiple circuit variants. (It's not worth mucking with the PoE design for small-scale builds; the reference design might be a bit more expensive but you get that money back on way less trouble to deal with.)
- willis936 1y ago
  The chassis net should be passed through the cable shield and the power isolated to force the current return through the cable in case power ground is bonded to chassis (which is commonly done, not sure why, I prefer a 1MOhm standoff). While not perfect this link is concise and provides handles to the relevant specs. https://www.brainboxes.com/faq/power-isolation-in-poe-ethernet-switches https://www.brainboxes.com/faq/power-isolation-in-poe-ethern... Yeah, TVS before any other silicon junction. It's nice to throw a single-use medium or slow blow SM fuse before the TVS to open circuit in device faults. This is going to be individual preference. I like the density and low design risk of fully integrated solutions like Microchip's PD70224. As long as you spec your FETs appropriately you can't go wrong with TI or AD options (VDS of at least 100 V, ID of at least as much current as you want to cram through with healthy headroom, RDSon that makes you happy, VGS that's compatible with the datasheet charge pump, size and cost that doesn't make you weep). When in doubt, stay very close to the datasheet's design. I just saw that the PD70224 is not recommended for new designs. What an awful day to have eyes. Oh, it's been superseded by the PD70288. Much lower RDSon, but a huge 8x8 package. The charge pump is mysteriously gone and there is now a UVLO of 24V. This is more PoE-specific, which is less generally interesting to me. If only someone would sell me an ideal diode full bridge rectifier IC with integrated FETs, OCP circuit breaking, UVLO, OVLO, a fault flag, control input, and current monitor, I'd never buy a different power entry IC.

Animats 1y ago

Not clear on how multiple sources on the same cable work. Is that allowed? Is there a power break at midspan, or does power flow through? How are the regulators coordinated?

eqvinox 1y ago
There are never multiple sources; a midspan PoE injector breaks the power flow and injects only its own power supply. It's done through the center tap on the Ethernet transformers. Midspans have another set of those transformers and inject the power on the PoE PD facing side. Whole pair(s) carry common-mode DC current, so basically your green pair could be ±48V and the orange pair 0V. If any, the upstream switch's injected power would just end at the other coil of the Ethernet transformer in the midspan. However, the midspan also doesn't pass through PoE negotiation, so the switch won't turn on power to begin with.

RandomBacon 1y ago

Question for anyone who might have a suggestion: I have a Ring home security system. I would like to get an offline home CCTV that only records when the alarm is set (either in Home or Away). A quick internet search does not show an API. I'm not sure Ring has a device that I could wire a relay (if that's the right thing) to.

dang 1y ago

[stub for offtopicness]

davydm 1y ago
came for the poetry, left with an engineering lesson
leoh 1y ago
I'm just, like, vibe-coding, man. Why do I need to know about PoE?
scuff3d 1y ago
Not gonna lie, I'm kind of disappointed this isn't a Path of Exile tutorial for engineers.
elromulous 1y ago
"every engineer"? Should a chemical or nuclear energy engineer have to know about PoE?
- ThrowawayTestr 1y ago
  Sure. It's really useful if you're setting up a home security network.
JoshGG 1y ago
POE. Purity Of Essence ?
varenc 1y ago
you're a hero

sema4hacker 1y ago

POE switches can have more jacks than they can provide power for. I have five pan-tilt-zoom (PTZ) cameras but learned they can need up to 40 watts each, preventing plugging them all into a particular POE switch I had. Chaining a couple of switches solved the problem, be beware how much power your devices need to consume.

ifwinterco 1y ago
Is it actually likely that all 5 would be drawing full power at once though? It's normal in household wiring (at least here in the uk) for circuits to be somewhat undersized based on the concept of "diversity" (i.e. it's highly unlikely every socket on the circuit will be drawing 13A simultaneously)
- publicmail 1y ago
  I would expect power consumption to be fairly consistent for something like a surveillance camera that emits a stream 24/7.
  - bombcar 1y ago
    Not if they’re PTZ; they’d obviously be drawing more power when panning, tilting, and (maybe) zooming if that is mechanical.
Underphil 1y ago
This is true of any electrical system, no?

ww520 1y ago

It is also good on delivering power to AES50 snake stage box to microphones that needs fathom power.

red369 1y ago

I recently needed to buy a new power supply for my Mikrotik router (hAP ac²), so I decided to just buy a Ubiquiti PoE injector instead. It feels magical to have the PoE injector tucked in a cupboard with the optical network terminal, and outside Narnia, the router has only one cable going to it. Also, the Ubiquiti PoE injectors are particularly satisfying. Powered by standard AC cables, and a nice simple design. Now that I've experienced this magic, I'm not going back! However, as much as I love the hAP ac², it only accepts passive PoE. I don't love passive PoE - it scares me! Unfortunately, it seems like most (all?) Mikrotik routers only accept passive PoE. Does anyone know of a good alternative when it comes time to replace my router? I would have liked it to be Ubiquiti, but I don't usually read positive things about them around here.

bombcar 1y ago
You can get the inverse of an injector that takes active PoE and makes a barrel plug out of it.
- red369 1y ago
  Thanks for reminding me of that! I considered that when I was finding it hard to find a passive PoE injector. It's not quite as tidy, for example, with the router sitting visibly on a desk, but it's close. And you're right that it could work for anything.
  - sodaclean 1y ago
    I converted my Hue Hub to PoE with a splitter. It's super convenient but not the prettiest.
nucleardog 1y ago
> It feels magical to have the PoE injector tucked in a cupboard with the optical network terminal, and outside Narnia, the router has only one cable going to it. Last time I remember feeling like that was the day I unplugged a RB5009 and it... just kept running. Was standing there holding the power cable in my hand, clearly unplugged, and the router was sitting there still happily blinking away. Like, this clearly can't be possible but I'm staring right at it and it's happening. Took me a minute, but eventually realized the Starlink box that provides power to the dish _also_ provides power on the local side for their provided router as well, and apparently it was happily powering mine now.

mns 1y ago

PoE actually saved me, or at least helped me simplify some things. My router is in one place, while the distribution box where all the cable conduits lead to every room in another place. The distribution box (where also the optical cable originally comes from to the router) has no power plugs. I wanted to have Ethernet plugs in every room (especially for any fixed devices), so I managed to find (quite difficult in Germany) a PoE powered switch for the distribution box with no plugs available, get a PoE injector to power it and from there on to wire and install Ethernet plugs in all rooms.

le-mark 1y ago

Can anyone comment on what VEX robotics kits do with POE? Their controller box connects to motors via cat5 (they call them “smart cables”)which carry’s power, pwm, and encoder data. I don’t think it’s carrying ethernet but could be? Any sources for more info would be appreciated!

lawik 1y ago
It seems to be RJ11 and they might be spec:ed slightly differently (thicker leads?) to power motors. I get the impression it is mainly to control what can be used in competitions. This was what I found from skimming around: https://www.robotevents.com/V5RC/2018-2019/QA/35 https://www.robotevents.com/V5RC/2018-2019/QA/35 I doubt it is Ethernet at all, so it wouldn't be Power-over-Ethernet. Just some useful connectors and wires making for an appropriate cable. Also seems like you can make your own perfectly fine. Or they might melt. I suppose try it.

zara762 1y ago

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gwbas1c 1y ago

Is POE really relevant in the consumer space? All of my laptops get power and wired data through their USB C port. Does it make more sense to just send data over USB C? For example, my Chromecast gets power and wired ethernet through its USB C port. (I have an official Chromecast power brick that I plug an ethernet port into.)

qwertyuiop_ 1y ago
You wouldn’t have to worry about POE in the device category you mentioned.

sota_pop 1y ago

As an EE, once upon a time had a rep pitch PoE lighting fixtures. Cool idea, like allowing each individual fixture to be addressable/ controllable on a BAS, but they just had too many gotchas like coupling lighting (and by extension life-safety systems) to the server/network, additional voltage drop considerations, etc. Otherwise and for network gear, I really like PoE!

qaz147 1y ago

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qaz147 1y ago

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viggity 1y ago

I worked for a PoE lighting company for a couple of years. Yes, the ability to program your lights based on time of day, occupancy sensors etc was all nice for the end consumers. But the big advantage was that since it didn't use mains power, the owner of the building didn't have to hire a union electrician at eleventy gillion an hour to move some light panels around in a drop ceiling.

parliament32 1y ago

Something I've never understood: > The above figure shows a PoE injector with auto negotiation, a safety and compatibility feature that ensures power is delivered only when the connected device can accept it. Before supplying power, the injector initiates a handshake with the PD to detect its PoE capability and determine the appropriate power level. If PoE requires negotiation, and the device requires PoE for power.. how does it perform the handshake without being powered/booted first?

_flux 1y ago
Presumably lower voltage/current is provided first?

bokohut 1y ago

Quite the mix of comments in 2025 from something that has existed and been foundationally critical in many unseen systems. I designed and built my first POE system in 2004, at my own house as a dogfooding POC, and that system stills works to this day. Since that time I have built and installed many more without issue that continue to move along doing what they were intended to do, protect life and property via recording activity privately. My own home footage has been called upon several times by law enforcement and was critical in convicting at least one home break in crew. The benefit of install is simple to comprehend for those with significant experience in the electrical field, run one small wire for data and power and ensure the POE supply is on a battery - done. Additionally I add those using WiFi for security are laughed at daily as losses pile up, web search MLB player home break-ins, as running a hardline cannot be jammed but many foolishly put all their assets solely behind WiFi security. Also these surveillance systems require no external cloud by design so no one is watching remotely, unlike the Fed and State viewing your Ring cameras for years and now which recently partnered with Flocker. No one cares more about you than you so if someone is selling you security ask yourself what it is you are actually paying for. In closing, as we move into a new era of technological efficiency forced by rising energy prices and costly electrician labor hours, one is going to witness an uptake of POE adoption in more and more nontraditional places. It is already happening and its moment will come as more recognize the cost benefit to this greatly simplified power delivery method with integrated battery backup. What you cannot see matters most!

outofmyshed 1y ago

Passive PoE getting a lot of stick in the comments, but for one-off point solutions, it’s fine as long as you know what you’re doing. I have it to run a couple of MikroTik devices in awkward places and not having to run wall warts and flimsy DC cables around the place is very handy. My next switch upgrade will be a proper PoE+ one, but it’s not justified yet.