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.)

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.

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.

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?

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)

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?

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!

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.

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.

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?

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?

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.

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!

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.)

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!

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.

1. Why are IEC/Edison cables so thick if Ethernet can carry the equivalent power?

2. How does PoE compare to Powerline Networking?

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

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.

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.

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