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Power-Over-Ethernet (POE) has come up in several answers recently as potential solutions to problems involving wiring and getting power to strange places.

How does POE help the DIY person in achieving a result ? Samples:

Criggie
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    I think the goal here is to make a post that can be linked to in the future for people who might benefit from learning about PoE. Kinda like the tandem breaker question or backstab question. This seems like a good idea, in my opinion. – maples Jul 03 '22 at 01:28
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    I don't mind downvotes, but do feel free to comment and say why. I'm sure this question could be improved, somehow. – Criggie Jul 03 '22 at 03:13
  • Upvote for answer but how is this a specific DIY question? We are question and answer format not discussion that may be the reason ??? I usually reverse downvotes without a reason but this may be more a discussion than question answer as the site guidelines instruct. – Ed Beal Jul 03 '22 at 07:10

2 Answers2

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Power Over Ethernet is a codified way of safely sending up to 15 Watts of electrical power over a twisted-pair ethernet cable.

POE puts -48V DC on the wire in such a way that it does not interfere with ethernet communications.

There is no requirement to make use of the Ethernet part!

As such, you can run up to 100 metres (and maybe further) to provide power to a location that doesn't have mains AC available. In many locations, such an outdoor run of wiring requires a professional qualified electrician, along with reliable water sealing on all connections.

Anyone with the right tooling can install twisted pair cabling. There's some technique required, but no qualifications or official certifications are necessary. (feel free to add corrections to this if you know different)

How?

You can choose to add the power to a wire using either

  1. A POE Injector (moderate cost for 1 or 2)

enter image description here
From http://gowifi.co.nz/power/active-poe-injectors/pt-pse100gf.html

A POE Injector is a box that adds the power, and has an ethernet in and out port along with a mains power lead. If you have more than 2~3 items to power then a switch might work out cheaper.

  1. POE-enabled switch (more expensive)
    This functionality can be included in an ethernet switch like a Netgear 300 Series SOHO Unmanaged Switch (model GS308P)

enter image description here
from https://www.netgear.com/nz/business/wired/switches/unmanaged/gs308p/

Note the one above only has 4 POE enabled ports not 8.

Getting the power out of the cable:

If your remote device is POE enabled then the only thing required is to plug in the ethernet cable. The unit will negotiate POE with the injector/switch at the far end, then after a few seconds delay will turn on and start working.

Otherwise you'll need a POE Splitter which does the same negotiation but in a separate package.

enter image description here

The voltage at the far end is set by the splitter, where 5V or 12V is common and sometimes has a USB micro or C plug or a barrel plug. You'll buy the splitter to suit your device's voltage requirement.

There are even cheaper "power over twisted pair" adapters or Baluns that forgo any kind of negotiation and just smash 12V onto the pairs using your existing wall PSU.

enter image description here
From https://www.aliexpress.com/item/4000575451173.html

Your existing PSU may not have the "oompf" to drive effectively the whole length of this "extension cable", so may not work, but they're cheap.

There are different POE standards that allow for up to 15W, then 25W, then 51W then 71W and doubtless more. Each increased standard requires better cabling and/or shorter maximal distances.

15W is more than enough to run a LED light fixture, and I have a raspberry pi and a 5TB USB hard drive running off one link.

In the linked question about "solar lights in shade" POE was workable.

enter image description here

The building in the left of photo has AC power, bridge is under 100 metres from building. A single POE run would supply enough power to run 4x3 watt 12V LED lights, or 3x5 watt lights. Running four separate wires would allow a single 15W light on each wire and some redundancy.

Criggie
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    One point on the PoE for my case (the one with the photo): The distance would make it workable and it wouldn't be too hard to wire it in, but, ultimately, I decided it would be a problem. We've had multiple instances of lightning strikes in the area blowing out equipment - until I made sure all underground lines are fiber optic. I've seen places where this isn't an issue, but since it's a known issue here, I am quite hesitant to run ethernet underground - even with lightning arresters. – Tango Jul 03 '22 at 03:31
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    There are at least two states I do not work in as they have highly restrictive low-voltage licensing requirements. There are probably other LAHJs where that's true. In both cases the way the requirement is structured is clearly more about "turf" than safety (no reciprocity, and the only way to get the license is to spend an inordinate amount of time working in that state under someone else with a license from that state, and pay a bunch of fees along the way.) – Ecnerwal Jul 04 '22 at 17:55
  • @Ecnerwal interesting - can you name the states? Do the restrictions apply for DIY homeowners or just to commercial electricians working for hire ? – Criggie Jul 04 '22 at 18:22
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Pulling a single lightweight, flexible cable is simpler than pulling that same network cable and a power cable. As long as the power needed is small enough, you can kill two birds with one stone (or, one ethernet cable).

The usual hardware for which this solution works are Wireless AP nodes and Video-over-IP or Video-over-LAN cables. I cabled the former into my house and had I needed to run electricity separately to the same sites, I probably wouldn't have bothered in the first place.

gowenfawr
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