Power...Over An Ethernet Cable?

Power...Over An Ethernet Cable?
5 min read
13 April 2022

Hate tangled messes of cables? Sick of always having to stay close to an outlet? Well, there's actually a way to power certain devices without having an outlet anywhere nearby. And I'm not talking about a battery. I'm talking about Power over Ethernet or PoE.

The basic idea is simple. A single ethernet cord carries both power and data, allowing you to say, "Never more to a separate power cable. And you don't even need any special ethernet cable. Most of us use Cat 5e or Cat 6 these days for internet, and either one of these will work just fine. But unfortunately, you can't just connect any two gadgets with an ethernet port and expect power delivery. Power...Over An Ethernet Cable?The client device and the router or switch you're connecting it to both have to support PoE. The good news here though, is that PoE switches typically don't cost that much more than regular ones. But what kinds of things really benefit from having PoE to begin with.

One big one is wireless access points. You can often get better Wi-Fi performance by using a standalone access point instead of the one built into your office shelf router, and many of these access points support Power over Ethernet. This can be useful at home, but it's especially common in larger commercial or high density environments that need multiple access points across far-flung distances where it would be impractical to run both ethernet and the power cables.

There are also PoE clocks available in both analog and digital. A single ethernet cable both provides power and connects the clock to an internet time-server, so you'll never have to worry about setting the clock or changing the battery. And yet more applications include VoIP, where one ethernet cable going to your desk phone gives you voice capabilities and power.

Intercoms, smart door locks, and surveillance cameras can all also use PoE. Basically, anything that needs a constant data connection, but doesn't have massive power requirements can benefit.

But hold on a second! How the heck does a regular ethernet cable carry both data and power? So you can send data and power on the same cable because the ethernet protocol moves data using something called differential signaling.

Basically, two signals are sent that have the same voltage, but one is positive and one is negative. The orientation of the positive and negative signals determine if the bit is a one or a zero. Power over Ethernet just applies a larger voltage to the wiring inside the ethernet cable. It doesn't affect the positive-negative difference of each bit, so data transmission is unimpeded.

But speaking of larger voltages, just how much power can PoE deliver? Well, there are actually a few different versions of the standard that deliver different wattages, which we've summarized here on this chart. Power...Over An Ethernet Cable?Those higher wattage versions are useful for devices like high powered wireless access points or rotating cameras that need the extra wattage to turn a motor.

So yeah, all this sounds pretty cool. But before you rush out to buy a bunch of PoE-enabled stuff like their Pokemon cards, keep this caveat in mind. Many PoE devices don't even have a regular power port, and so can only be powered via PoE. And if you don't have a switch or router with a PoE port, you'll need to pick up something called a PoE injector. And don't worry, this isn't some kind of weird cyber syringe. Rather, it's a little wall wart that plugs into a standard outlet, but also features a pair of ethernet ports. One connects to the client, and the other to your router or switch. Just make sure the standard supported by the injector is at least the same as what your client device needs to ensure it gets adequate power. You can even combine an injector with a PoE splitter and power a non-PoE client as well!

Also remember that PoE has a maximum range of 100 meters without a repeater. And while that's a fairly long way, you can eat through that fast if your cable run has lots of twists and turns. 

Den W. 3.1K
I'm a passionate tech enthusiast who loves diving into the world of software, programming, and tech reviews.
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