Plugging non-PoE Devices Into PoE Switches: Will It Go BANG? (Power over Ethernet Dos & Don’ts)

I’ve recently purchased a bunch of Power over Ethernet (PoE) cameras for my home’s security system, and so I started looking into powered network switches – in other words, PoE compliant switches. But are they ‘safe’ to use? After all, they send electricity down the Ethernet cable?!

And what happens if you accidentally plug in a normal (non-PoE) device into a PoE switch?

I explore all this – and more – in this video… including via a VERY suspect looking demo! I combined TWO power over Ethernet switches with three non-PoE devices (a HP printer, DVD player and TP-Link Gigabit switch), and turned it all on!

https://www.youtube.com/watch?v=kNP5sC-aPmo

If you prefer text over video, please read on for the guide/transcript version of this video.

Video Transcript & Guide

Intro

Hey everyone, power over Ethernet is an AWESOME technology. It allows us to run a single cable – Ethernet – to a device, and it’ll MAGICALLY receive internet and power without having to plug it into a wall outlet. That’s because Ethernet cables contain EIGHT individual wires:

And some of these can be used for internet data, and some for power – although in some cases you can use the same wires for both:

Either way though, if THIS has electricity surging through it, what happens if I plug it into a normal device that does NOT support power over Ethernet?

Sketchy Demo

Well in the MAJORITY of cases, nothing bad will happen – I hope. Let’s take a look! This is a Mercusys PoE switch, which I then connect to two non-PoE devices: my HP printer, and a TP-Link Gigabit switch. Because I’m a MAD LAD I then plugged in ANOTHER PoE switch, before connecting this to a DVD player – which also does NOT support power over Ethernet:

I haven’t actually pre-tested this, but in THEORY it will work. I hope so, anyway, because my wife said that she needs to use the printer in half an hour to print loads of documents. Uh gosh, here we go – let’s turn this all on.

[Explosion Sound] Just kidding. It’s actually all fine – the DVD player still boots up and is listed in my Eero app, meaning that it’s connecting just fine to the network despite being connected to a power over Ethernet switch and y’know not supporting power over Ethernet. The HP printer is also working fine and it’s actually printing right now.

So that proves that you CAN plug “normal” devices into a powered Ethernet switch without any problems, but why is this? And are there any dangers? Well, yes.

How PoE ‘Should’ Work

It all boils down to HOW the power over Ethernet is implemented by the switch. A “proper” PoE switch will first negotiate with the plugged-in device to “agree” on whether to JUST send internet traffic, or power as well:

This occurs as part of the initial handshake process, where the device is registered onto the network. If a device does NOT support power over Ethernet, then the switch will just send standard internet traffic from that particular port – without any power. But if the device DOES support powered Ethernet, then both internet and power will be sent down that cable:

Simple. THIS is known as “active PoE”, because the power is actively agreed between the switch and device.

Passive PoE

There is another type of switch, though. Passive PoE switches. These ARE less common, but you can still buy them easily enough on Amazon and other shops – so it’s easy to make this mistake:

Passive switches will ALWAYS send power and data. As you can imagine, plugging a non-PoE device into a passive switch will cause you issues, because unexpected voltage will be sent down the Ethernet cable and into the device. In the worst case, this will cause a burn out – either of the device, or the device’s ethernet port.

So, why does passive PoE exist? Well, they’re often cheaper to produce – meaning that they’re cheaper for us consumers to buy (see how the passive switch is £10 cheaper below?):

If you know that all your devices WILL need powered Ethernet, it could make sense to just buy a passive switch and save some money.

PoE Splitters

Plus if you find down the line that you’d then like to plug in a non-PoE device, you’re not completely stuck. While “upgrading” to an active switch might be best in an ideal world, you could explore PoE splitters instead:

These are kind of like the opposite of PoE switches and injectors. You plug a powered Ethernet cable into the PoE splitter, and to be ultra-technical, it “sucks” all the power out of the Ethernet cable [sucks cable] [laughs] Sorry I don’t know why I done that! You’re then left with a DC output and a standard Ethernet port, meaning that you can then safely use the Ethernet port – and cable – on your non-PoE devices.

Final Thoughts

That’s one option, anyway. I think that I’ll personally just carry on buying ACTIVE power over Ethernet switches because I know that they’ll safely negotiate whether to send power or not. But what about you? Have you ever used passive power over Ethernet? Or maybe do you just avoid PoE altogether? I’d love to hear your thoughts down in the comments.

And that wraps up today’s video, I hope you found it interesting. If you did, please click the thumbs up button. Please also subscribe to my channel if you haven’t already, and thanks for watching.