Power over Ethernet (PoE) – All You Need To Know

This blog is all about Power over Ethernet, an essential system for many technicians across many sectors nowadays. if you were wondering what is PoE? How does PoE work? Should I use Power over Ethernet? In the blog we discuss all you need to know about powering devices over data/ network cabling. Let’s begin.

What Is Power Over Ethernet?

Power over Ethernet, which is most commonly abbreviated to PoE is a system where power is provided via the same data cable that provides the data/ Ethernet connection meaning no separate power supply is required and devices can be powered “remotely” if there is no nearby electrical power connection near the device that requires power. This makes it perfect for exterior connections where no power is generally available. It can greatly simply installations and provide a for a much more neat and professional finish.

What Is PoE Used For?

It is commonly used for powering of WIFI access points, CPE, VOIP phones, IP Cameras, door entry/ access control systems, and many more. Utilising PoE for your installations means that only twisted pair data cable is required at your Powered Device (PD) which will provide both data and an electrical power connection.

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How Is PoE Inserted Into a System?

PoE is entered into a system by Power Sourcing Equipment (PSE) which provides the power to the Powered Device. It is typically inserted via a standalone PoE injector or a compatible network switch. The injector or network switch will be connected to a mains electrical connection as well as a data connection.

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PoE Injector

A PoE injector is a device that injects the DC current onto the Ethernet cable to power the Powered Device. Most PoE injectors have two RJ45 connections, one for a connection to the LAN for an internet connection and the other to the device providing a data and power connection. These are usually labelled LAN and PoE or something similar. It’s important that you connect the cables the right way around as to do it incorrect will see the DC power flow the wrong way into the network, which could cause problems or damage to the equipment and the device not receive the power it requires.

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PoE Network Switch

If you need to provide a power to multiple locations, like is required to feed multiple IP CCTV Cameras or multiple wireless access points(AP’s), you could connect them to a standard switch/ ethernet ports on a router and feed to cables into multiple PoE injectors which can power each device independently. The problem with this type of set up is that the installation can quickly become messy and provide the network with an unnecessary amount of failure points. A far more efficient solution to this would be to install a PoE switch, which can provide PoE to multiple devices as the same time. Many switches come with configurable input/ outputs which allow for the switching off of PoE (for devices where PoE is not compatible or required) and/ or changing the output voltage to match the device you wish to power.

Network Switch Powered By PoE

Nearly all PoE network switches that can be purchased, provide power to other devices. But what if you required a network switch that itself was powered by PoE? For instance, you may have several data cables in one position but no where to plug a network switch in to power it. Fortunately, these do exist. If you need something like this, you require a switch that itself is a Powered Device (PD). Pass Through Switches exist which are both a PD and Power Sourcing Equipment, meaning they can be powered remotely and also power other devices simultaneously.

IP CCTV NVR

Many Network Video Recorders (NVR) used with Internet Protocol(IP) CCTV systems come with with a built in network switch to directly provide power to each connected CCTV camera, meaning that no separate PoE switch or injector(s) is required.

Active PoE

Active PoE refers to a device that will automatically negotiate the correct PoE supply for the powered device. This means that you do not have to worry about the Power Supply Equipment (PSE) providing too much current/voltage or power to the Powered Device. If the device does not support Active PoE, no power will be provided. This can help prevent any potential damage to other Powered Device.

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Passive PoE

With Passive PoE, unlike Active PoE no negotiation takes place so the equipment will not automatically assign the correct power requirements between the Power Supply Device (network switch or injector) and the Powered Device. It will provide power over the Ethernet cable whether the device supports it or not. Care and attention needs to be taken when installing Passive PoE equipment to make sure that the correct power will be supplied to the device. It helps if you use the same manufacturer equipment for both but even some will change the PoE requirements on their equipment. For instance, Ubiquiti uses both 24V and 48V for their Unifi products.

What Voltage Does Power Over Ethernet Use?

Most PoE products use 48V DC, but some systems/ standards operate between 24V and 57V. The amount of volts/ watts provided by the Power Supply Device will depend on the PoE standard that the devices use.

PoE Standards

The are numerous standards used by PoE which can be used for adjusting the power requirements for each device. The common names for these are PoE, PoE+, and Ultra PoE. More information on each standard can be found below.

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Common Name                Standard                              Power Output

PoE                                    IEEE802.af                          15.4W

PoE+                                  IEEE802.at                          30W

Ultra PoE

4PPoE

UPoE                                 IEEE802.bt (part 3)             60W

Ultra PoE

UPoE                                 IEEE802.bt (part 4)             100W

Maximum Cable Length of PoE

Most PoE systems will work at a suggested maximum cable length of 100m before the voltage drop will become too great. In practice, with a good quality cable you may be able to extend the limits by a little bit. If a longer cable length is required, you could either move the PoE injector closer to the Powered Device or you could install a PoE repeater to extend the maximum cable length.

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What Cable Do I Need For PoE?

I would suggest that for any network installation or installation utilises data cabling, that Cat5e data cable should be used as a minimum standard. Cat5e is suitable for all forms of PoE standards, which means that higher spec cables like Cat6, Cat7, are also compatible. You may also want to consider using screened cables and connections as these provide superior grounding.

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Questions Regarding Power over Ethernet Connections

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Until next time,

Tom