How do you power a network-connected device like a VoIP phone or IP camera? You plug it in, right? Three prongs into the surge protector — done.
But actually there’s another way: Power Over Ethernet or PoE. We’ve covered what PoE is in the past: you deliver power to the device via the same Ethernet cable that connects the device to the network.
PoE eliminates the power cable, so you don’t need to worry about where the wall plug is anymore while decluttering the office. You can run Ethernet cable without needing an electrician — big savings. It’s a very useful thing, PoE. It’s an open standard, too, so compatibility isn’t a big issue.
How do you deliver Power Over Ethernet?
When it comes to PoE, there are three devices to know about: a PoE switch, a PoE extender (a.k.a., PoE repeater), and a PoE midspan (a.k.a., PoE injector).
A PoE switch is a standard network switch that you use to connect devices to the IP network that also can deliver power to those connected devices. Makes sense.
A PoE extender or PoE repeater does exactly what you think: it extends the range of the power. PoE has a limit of 100 meters (328 feet), that is, there can be only 100 m of cabling from the PoE switch or PoE midspan to the device you want to power. But what if you want to power something farther than 100 m away? You need a PoE extender. Makes sense.
PoE midspan is a bit of a more obscure term.
In this blog, we explain what a PoE midspan is, when you should use a PoE midspan, and what features you need to look for when shopping for a PoE midspan.
Let’s get into it!
An Introduction to PoE Midspans and PoE Injectors
First, let’s get a bit of terminology out of the way:
PoE midspans are also known as PoE injectors. They’re known as midspans because they sit in the middle of the span of cabling running from a switch to an endpoint. They’re known as injectors because they inject power into an Ethernet cable that otherwise isn’t carrying power.
To keep things simple, we’re using the term midspan. It’s probably the more common of the two terms, although you’ll run into both regularly.
How Do PoE Midspans Work?
PoE midspans are a very simple device.
Picture the standard way of connecting a VoIP phone, for example, to a network switch: you plug one end of an Ethernet cable into a port on the switch and the other end into the appropriate port on the phone.
With a PoE midspan, you plug the cable from the switch into the midspan, then run another Ethernet cable from the midspan to the phone. The midspan itself you plug into an electrical outlet.
That’s it.
The midspan is not a switch. It doesn’t manage data flows or anything. It simply adds power.
When Should You Use a PoE Midspan?
PoE midspans are used when a PoE switch isn’t available or can’t deliver the amount of power required.
PoE switches are typically more convenient — one less device — but there are valid reasons not to have one.
The first reason is simple: cost.
A PoE switch costs more than an equivalent non-PoE network switch, and if you only have one or two devices that you need to power via PoE, it can be more cost-effective and convenient to buy a midspan or two than change to a PoE switch.
The second reason is a bit more complicated. A midspan is used to deliver more power to a device than a PoE switch can deliver.
Take an Axis PTZ camera like Axis P5654-E Mk II. An elite security camera like this requires a lot of power, especially in cold-weather locations where the camera has to run a heater at the same time as recording video.
The Power Over Ethernet standard is actually a series of standards for delivering increasing amounts of wattage. If you’d like to know more about the different PoE levels, check out our blog, “The Ultimate Guide to Using PoE (Power Over Ethernet) to Power IP Devices.”
PoE switches and PoE midspans can support different levels of PoE power delivery, just like regular power supplies support different wattages. Switches that support PoE++ or High PoE (which are just names for some of the higher wattage levels) are rarer and more expensive than standard PoE switches.
If you have a PoE switch that you use for VoIP phones, which don’t require much power, and you want to add a power-hungry PTZ camera, your PoE switch might not be able to deliver enough power.
In this case, using a PoE midspan that can deliver the required amount of power is the best option.
This reason also highlights the most important feature to look for when shopping for a PoE midspan: does it provide the required amount of power? More on that in a second.
What Devices Use a PoE Midspan?
Any device that can be powered by PoE can be powered by a PoE midspan. This includes VoIP phones, IP cameras, video bars, touch consoles, wireless access points, IP paging speakers, and many more.
Some manufacturers have actually replaced the traditional power supply with a PoE midspan. For example, the Poly Studio X32 Video Bar doesn’t use a power supply. It uses a PoE++ midspan.
Some devices don’t have traditional power ports. They can only be powered via PoE. If you don’t have a PoE switch, you’ll need a PoE midspan for these devices.
Features of PoE Midspans to Look For
When looking for a PoE midspan, what features should you emphasize?
PoE Class (Wattage)
The most important feature of a PoE midspan to look for is its power-rating. This will often be given in wattage — a 15W midspan or a 60W midspan, for example — but the more accurate way of ensuring compatibility is to look at what PoE standards it covers and ensuring that it covers the standard the device needs.
There are three PoE Standards: 802.3af, 802.3at, and 802.3bt. The amount of power goes up for each. The Standards are further broken down into Types and Classes, which incrementally cover more and more power.
In our guide to PoE that we linked to earlier, we have a full breakdown of all the different PoE types.
So if your device says it is a 802.3at Type 2 Class 4 device (equivalent to 25.50W) and your midspan only covers 802.3af Type 1 Class 3 devices (equivalent to 12.95W), well — that ain’t gonna work.
With outdoor IP cameras, it’s particularly important to check the datasheet or manual for the power requirements, because the requirements can vary depending on temperature. If the camera has to heat or cool itself on top of taking video, then it’ll require more power. But if you live in a temperate location that doesn’t have extreme heat or cold, then you might not need to deliver as much power to the device.
Durability
If you need to use a midspan outdoors or in a harsh environment like a factory, you need to make sure that the midspan is built to handle the challenges.
For example, PoE midspans are often used for power-hungry IP cameras that are mounted outdoors. The camera might be rated for outdoor usage — but is your midspan?
Where are you going to mount the midspan? Can it handle the temperature? Is it resistant to water, dust, and so on?
You have to make sure that the midspan can handle the environment.
Ethernet Port
PoE midspans are Ethernet devices, which means they support different Ethernet standards. If you want a Gigabit Ethernet connection because you’re using a video bar for an important video conference with a new client, but the midspan only supports 10/100 Ethernet, the midspan can create a network bottleneck and damage the quality of the video call. Not good.
Make sure the midspan is rated for the Ethernet speed you desire.
Other Features
There are a few other minor features to think about:
Power cable length. A midspan needs to be connected to an electrical outlet. Is the midspan’s power cable long enough to reach an electrical outlet?
Number of ports. Most PoE midspans are one-port devices, but there are some — like the Axis 8-Port PoE Midspan — that have more. If you want to power a bunch of devices without using a PoE switch, a midspan like that is an option.
Surge protection. Some PoE midspans are also surge protectors, which is great for protecting your devices.