Thursday, April 22nd, 2021

Power over Ethernet Explained: What’s PoE and Why It’s Totally Cool

You want to blanket your home with Wi-Fi, but extending electrical power to the far side of your yard or that tight corner in your attic can be a daunting task. That is where PoE, or Power over Ethernet, comes into play.

It’s a straightforward concept where you can kill two birds with one stone. There’s quite a bit to know about PoE, and you’ll find it all here, with a minimum amount of technical jargon.

A Power over Ethernet Setup
A typical Power over Ethernet setup, from bottom up: Router, injector, and a PoE device.

What is Power over Ethernet

Power over Ethernet is when you use one network cable — like a CAT5e or CAT6 one — to deliver both data signals and electric power to a device. So yes, you still need to run a wire, but just a single one.

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PoE: Cables and device types

PoE works with all network cables. Generally, though, a higher quality cable (pure copper) is always better for PoE than a lower-quality one (copper-clad aluminum).

As for network speed, PoE adheres to the general standards of network cables. Currently, PoE is available on Fast Ethernet (10/100 Mbps) and Gigabit Ethernet (1000 Mbps). But in the future, there will be multi-gig PoE.

Usually, plugging a device into power involves three items: the power source, the power cable, and the device itself.

Since you can’t connect a network cable directly into a wall socket, you need something at this end to facilitate the power draw.

In the world of PoE, this device is officially called a power sourcing equipment device. For the sake of simplicity, you can understand it as the power sender.

Now the device that gets electricity over the network cable is officially called a powered device or a power receiver. Let’s find out more about them.

Power sourcing equipment (PSE) – Power sender

A power sender is a device that works as the source of the power; you connect one end of the network cable to this device. This end also links to a router or a switch. A PSE device always has a power adapter to draw juice from a wall socket.

A typical example of a PSE device is a PoE injector (or a PoE adapter), a type of Ethernet coupler that also plugs into a wall socket.

Injectors are popular because they add PoE capability to an existing regular switch or router. Alternatively, there are PoE switches or PoE routers with built-in PoE injectors for some or all of their network ports.

To use an injector, just plug one end of a network cable into its PoE port.

TP Link PoE Injector
Power over Ethernet: A typical PoE injector (adapter) is a power adapter that has two network ports. The PoE port delivers both data signals and power to a Power over Ethernet end-device.

Powered Device (PD) – Power receiver

A power receiver is the end-device — such as an IP camera, an Wi-Fi access point, or a Voice over IP phone — that’s PoE-ready.

You connect the other end of the network cable to this device, and it’ll get both power and data signals. Unlike the case of the PSE above, you can’t add PoE to an existing device. Instead, the device itself needs to have built-in PoE capability from the get-go.

Sometimes, we have both PSE and PD in a single hardware unit. An example is when a PoE camera has a second PoE-ready network port to power another PoE camera in a daisy-chain setup.

Power over Ethernet standards

There are two types of PoE, active and passive. Both have a range of about 300 feet (100 m), which is the general max length of the network cable that connects a power sender and a power receiver.

Active PoE

Active PoE provides a safety mechanism for end-devices (PDs).

With active PoE, devices perform a power check, called a handshake, before power is delivered. As a result, if the incoming electricity doesn’t meet the requirements, the power receiver won’t power up at all.

There are two primary standards for active PoE, including 802.3af and 802.3at, both have the max output of around 50 Volt.

802.3af

Also known as Type 1 PoE. This standard is the original (defined in 2003) and currently the most popular. It can deliver up to 15.4 watts of electrical power. In real-world usage, however, generally, you can expect about 13 watts from it.

802.3at

Also known as PoE Plus (or PoE+) or Type 2 PoE. Available starting 2009, this standard provides up to 25.5 watts of power.

The 802.3at standard is backward compatible with 802.3AF in the sense that its power senders (PSE) can support 802.3af receivers (PDs). However, 802.3at power receivers (PDs) generally require an 802.3at power sender to work.

(At some point, there will be 802.3bt or 4PPoE standard that can deliver up to 90 watts of power. The primary targets of 802.3bt are smart-home and IoT devices.)

The main advantage of active PoE is when a device belongs to a particular standard, then it will work with all equipment of that standard, from any vendors.

Passive PoE

Generally, if a device uses PoE that’s not one of the 802.3x standards mentioned above, then it’s a passive PoE device.

This type of PoE generally uses a proprietary injector that accompanies an end-device (power receiver) and only works with that particular device.

Passive PoE doesn’t adhere to a standard, and the vendor, therefore, has the freedom to specify its own electrical specs. With passive PoE, electricity is passed to the end-device (PD) immediately without being checked for compatibility.

For this reason, generally, it’s a good idea not to use a passive PoE injector with an active PoE receiver and vice versa. That can be similar to plugging a 110V device into a 220V outlet.

So, if you choose to use a passive PoE end-device, it’s a good idea to only use it with a passive PoE power sender that comes with it. But for ease of use, many passive PoE end-devices (PDs) on the market also support active PoE.

TP Link OC200 Controller
An example of a Power over Ethernet (PoE) end-device (PD).

Why Power over Ethernet is cool

The way it works, PoE eliminates the need for a wall power socket near the end-device (PD) itself. And that implies two important things:

  • Savings: You won’t need to spend time (and money) to install electrical wiring and power sockets, which would require a licensed electrician if you want to do it right. Running network cables, on the other hand, doesn’t need a license and is reasonably straightforward. Network cables are also relatively affordable; you can find high-end CAT6 in bulk for about $150 per 1000 feet (305 m).
  • Flexibility: You can run a network cable to any place, including tight corners. Without the need for an electrical outlet, the end-device can stay anywhere, including outdoor areas.
  • Decluttering: PoE can significantly reduce the number of wires since you won’t need to use a power cord, making it an excellent choice for office devices, such as an IP phone.

On top of that, PoE is more reliable and the end-devices are also safe from common power-related issues, such as power-surge, overload, or bad wiring. In case of hazard, the power injector or the PoE switch would likely take the hit first.

PoE vs. Wi-Fi vs. Powerline

PoE extends a network to one device at a time and, therefore, cannot replace Wi-Fi. But it can enhance Wi-Fi coverage.

Using PoE access points, for example, you can easily extend your Wi-Fi network to an area that doesn’t have a power socket (like the ceiling of a warehouse or the middle of a big yard), without compromising the performance.

As for Powerline, it generally serves the opposite purpose of PoE. Powerline is useful when there are power sockets at a place where network cables can’t reach. However, in terms of network performance, PoE is much faster and much more reliable. That said, if you can choose between the two, PoE is the way to go.

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In all, if you live in a large home, have a large warehouse, or want to place a network device outdoor or at an odd place, PoE comes in handy. It’s a much faster and more affordable solution than installing power cables and receptacles.

How to set up a PoE connection

How to specifically put together a PoE network depends on the devices you use. However, they all share the same hardware setup process.

Here are the typical steps you can follow in in any order (make sure you don’t mix passive PoE and active PoE devices):

  1. Place the end-device (PD) where you want, connect a network cable to its network port. If it has more than one network ports, use the port labeled PoE or PoE in.
  2. Plug the other end of the cable to the PoE sender (PSE) — be it a PoE switch or an injector. If you use an injector, make sure you use the PoE port, then connect its other network port to your switch or router, using another network cable. (Note: You can use PoE via a patch panel or a long cable that consists of two short ones linked together via a network coupler.)
  3. Connect the PoE sender to the power and the existing network.

And that’s it. Now the Power over Ethernet end-device is part of your network. From the networking point of view, PoE and non-PoE devices are the same. The way they get power doesn’t affect how they function or their performance.

9 thoughts on “Power over Ethernet Explained: What’s PoE and Why It’s Totally Cool”

  1. Happy New Year Dong!

    Just got Starlink Beta and the PoE powers the dish and the router which is a very cool setup. However I have doubts the supplier router will be sufficient for the entire house. I would like to plug in my old router and based on my understanding I should be good to go, my old router will not ask for power so there should be no sparks or smoke…do you agree?

    Reply
  2. You mention PoE range of about 300 ft. If my Cat5e run is approaching this (about 250ft) and there is at least 1 maybe 2 or 3 couplers in-between (not including patch panel, keystone jacks, etc.) extending the cable run, do you think the PoE device will not function as intended? (PoE wireless access point)
    Trying to decide whether to get a PoE unmanaged switch or save some money and get a basic unmanaged switch 🙂

    Reply
  3. When connecting from the PoE power source device and the receiver, is it OK to use cat6 wire to go from a patch panel at the router to an RJ-45 jack for the receiver? I want to connect the camera and the PoE power source with short cables into the jack and the patch panel. Stated another way, do patch panels and RJ-45 jacks maintain the power from source to receiving device?

    Reply

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