The Ultimate Guide to PoE (Power Over Ethernet)

By ·Categories: Tech Explained·Published On: July 18th, 2023·8.2 min read·

What is PoE?

PoE stands for Power over Ethernet and it’s the ability to transmit power to a device through an Ethernet cable. This industry standard takes advantage of the fact that a single Ethernet cable can carry both data and power. Practically, this means you can connect your device to your network and power it at the same time using a single cable. Integrators, installers, and users alike love this feature because it eliminates the need for a separate power cable and/or power source for every device, making it easy to install.  It has been a game changer for connectivity and powering the IoT. 

For example, let’s say you want to install a gateway on the edge of your network. You don’t need to wire it for Ethernet and hire an electrician to install an outlet. You just need a single Ethernet cable connecting your powered device (PD) to the power source (a PSE).

What is PoE PD? 

A photo of an orange industrial Raspberry Pi OnLogic Factor 201 with a PoE PD ethernet port

PD stands for Powered Device. A PoE PD is a device that you can power with an Ethernet Cable. Some examples include:

  • Industrial gateway or industrial controller
    • For example, our Factor 200 Series can be configured to be powered with PoE. With this feature, you can install these small form factor, Raspberry Pi powered devices in many places you may have never thought possible. 
  • Surveillance IP camera
  • Wireless access point 
  • VOIP (voice over internet phone)
  • Smart signs and flat screen displays
  • LED lighting 
  • Retail POS terminals
  • Other IoT (Internet of Things) sensors and devices

What is PoE PSE? 

PSE stands for Power Sourcing Equipment. A PoE PSE is a device that transmits power.  Examples include a PoE Switch, Injector, Repeater (sometimes called an Extender) or even an industrial computer with appropriate capabilities.

A photo of a Karbon 410 showing it’s POE PSE capabilities

PoE switch

A PoE switch offers multiple Ethernet ports and combines the functionality of a switch and a power source. You can use it to connect multiple powered devices (PDs).

A photo of a PoE switch

 

PoE Injector

A PoE injector is a small device that you can use to connect your PD to a regular LAN port. The PoE injector connects to a power outlet and has 2 Ethernet connections. You simply plug the PoE injector into the wall and connect your data input into one of the Ethernet ports. You can then use the second ethernet connection to share data and deliver power to your device.

PoE Repeater or PoE Extender

The maximum cable length for PoE is 100 meters. If you need to put your device even further away from your PSE than that (aka – the far edge) you can use a PoE repeater or extender to double your distance. You install it between the PSE and the PD and the cable on each side can be 100 meters. Need even more distance? Some extenders allow you to daisy chain multiple extenders.

Industrial computer as PoE PSE

When configured appropriately, some industrial computers can serve as your power source. This can be extremely beneficial in many scenarios including:

  • Security and surveillance
    • You can connect multiple security cameras to a single computer that serves as your Network Video Recorder (NVR)
    • Check out our blog on LENSEC who leverage this functionality.
  • Machine learning at the edge
    • Check out our story on ‘IKE Solutions. They created a machine vision solution to monitor catch and safety protocols onboard fishing vessels with limited space. They created a machine vision solution using cameras that are powered via PoE. This enabled them to greatly reduce their hardware footprint and power requirements.

IEEE 802.3 Ethernet Standards

The standard for PoE is part of the IEEE 802.3 collection of Ethernet Standards introduced about 50 years ago. These standards were developed, and managed, by a working group of the IEEE – the Institute of Electrical and Electronics Engineers. You can check out their website for a great 50th anniversary timeline of the 802.3 standard. 

How much power can be delivered?

The 802.3 IEEE standard has evolved over the years. Each iteration delivers more DC power and thus supports more power hungry devices. All PoE devices (sources or loads) are interoperable. However, a new high power PD will not get the full power from an older or lower power PSE. The standard defines the different power levels as ‘Classes’. 

This higher power level is made possible by providing current through all four twisted pairs in a network cable and it can support high powered devices such as flat screens and laptops. Prior to that, the power transfer happened over two out of four pairs. Check out our table below for a comparison of the 802.3 IEEE standard releases. 

802.3 IEEE Release Comparison Table

NameYear IntroducedIEEE StandardPower to PDMax PowerEnergized Pairs
  • PoE
  • PoE Type 1
  • Classes 1-3
2003802.3af12.95W15.4W2-pair
  • PoE+
  • PoE Type 2
  • Class 4
2009802.3at 25.5W30W2-pair
  • PoE++
  • PoE Type 3
  • Classes 5/6
2018802.3bt5 51W60W4-pair
  • PoE++ 
  • PoE Type 4 
  • Classes 7/8
2018802.3bt5 71.3W100W4-pair

 

All PSE devices are capable of powering downstream devices with a power level equal to or lower than the sourcing capability. This means that a Type 2 compliant PSE can power both Type 2 and Type 1 devices. You must select the capabilities of the PSE based on the requirements of the downstream PD devices.  

What is a PoE Splitter?

A PoE splitter is a device that you can use when you need to power a remote device that is not a PoE PD and there are no outlets available. It essentially splits the data from the power: one Ethernet cable goes in, and 2 cables come out, one for power and one for data. 

a photo of a PoE splitter when a power charged ethernet cable goes in and 2 cables come out - one for power and one for network

Safety considerations

The IEEE standards define many safety considerations. There are multiple levels of classification and detection that occur between the PSE and the PD before the full voltage and power levels are transmitted over the system. This is done in order to ensure that non-PoE devices and non-compliant PDs are not damaged by high voltage on the Ethernet cable. This makes it safe to use PoE capable ethernet ports with non-PoE devices.  

In addition, if the PSE is not capable of supporting the full power required by the PD, the connection will not be established. This prevents brown-outs on the PD. Only after a valid detection and classification signature is provided, will the PSE provide the full requested power to the network port.  

Once a link between a valid PSE and PD is established, multiple levels of protection at both ends exist to ensure that both devices are operating within the established limits of the IEEE standard. The PSE or PD devices monitor the voltage and current through the Ethernet link. The connection will be severed if overcurrent or overvoltage conditions are detected. Automatic detection is done to re-establish the link between the PSE and PD once the cause of the fault is removed. 

Advantages of PoE

  • Installing devices is easier. There is only one cable to run for both power and data.  
  • There is no need to hire an electrician to wire for an outlet in hard to reach places. If you need to install hundreds of devices, the savings on this can be significant! 
  • In general, there are fewer points of failure thanks to the reduction in equipment and cabling necessary to deliver both power and networking capabilities. 

OnLogic industrial computers with PoE

OnLogic offers many industrial computers that can be used to power your PDs. This can make your installation less complicated and minimize space requirements. Some examples outlined below. 

Karbon 300 and Karbon 700 Series

For example, the Karbon 300 and Karbon 700 Series provide three GbE LAN ports. You can configure two of these LAN ports to deliver PoE. The two ports will provide up to 32W of combined power. This power output is enough to support a single port up to 25.5W (IEEE 802.3at), two ports up to 15.4W each (IEEE 802.3af), or two ports with a combined draw up to 32W (e.g. 7W and 25W). 

Need to power more devices? You can configure the K700 with optional ModBay cards that can be configured to add up to four additional PoE ports. The ModBay PoE power output depends on voltage input, total system power draw, and operating temperature. The ModBay PoE card supports up to 30W per port at 70°C with a total output of 110~120W using 36V input, 105~120W using 24V, 75~90W using 12V, and 60W using 9V. The power output range for each voltage input is dependent on system configuration and total power draw. You can review the K700 product manual. 

Karbon Series

Karbon 800 Series

Our Karbon 800 Series features up to six 2.5 GbE LAN ports of which two can be configured to deliver PoE. The two ports will provide up to 32W of combined power. This power output is enough to support a single port up to 25.5W (IEEE 802.3at), two ports up to 15.4W each (IEEE 802.3af), or two ports with a combined draw up to 32W (e.g. 7W and 25W).

The Karbon 800 also supports additional LAN expansion using OnLogic ModBay cards. You can configure using ModBay cards to add up to eight additional RJ45 LAN or PoE ports, or up to six additional M12 X-coded LAN or PoE ports. Maximum ModBay PoE power output depends on the system voltage input, total system power draw, and operating temperature. For more information, you can review the K800 product manual.

Karbon 800 Series

How OnLogic Can Help

OnLogic has helped clients worldwide create a wide range of innovative solutions utilizing Power over Ethernet. Looking to power your own innovative solution? We can help! Reach out to our team today! 

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About the Author: Sarah Lavoie

Sarah Lavoie is a content creator for OnLogic. When not writing, she can usually be found exploring the Vermont landscape with her camera looking to photograph something amazing.