What is PoE (Power over Ethernet)?

Power over Ethernet (PoE) Definition

Power over Ethernet (PoE) is a standard that allows Ethernet cables to simultaneously transmit data and power using a single network cable. This allows system integrators and network installers to deploy powered devices in locations that lack electrical circuitry. PoE eliminates the expense of installing additional electrical wiring which entails hiring professional electrical installers to ensure that strict conduit regulations are followed.

I. What are the advantages of Power over Ethernet?

  • Cost-efficiency– PoE eliminates the cost of hiring professional electrical installers.  
  • Quick Deployment– PoE simply requires plugging in networking cabling to the proper equipment in order to function correctly.
  • Flexibility– Network administrators can deploy powered devices at nearly any location. Shielded cabling can be used for outdoor environments. Industrial-grade powered devices can be used for industrial environments.  
  • Safety– Because PoE utilizes a relatively low voltage, it presents low risks of electrical hazards.
  • Reliability– PoE falls under IEEE’s strict 802.3 standard umbrage.
  • Scalability PoE makes it simple to add new equipment to a network.  

The most common types of PoE utilization include:

  • VoIP phones
  • IP cameras
  • Wireless Access Points

However, PoE can also power other devices including:

  • PoE lighting
  • ATM machines
  • IP Intercoms
  • Security Card Readers
  • IP Clocks
  • Vending Machines


802.3af and 802.3at PoE Standards

The Institute of Electrical and Electronic Engineers (IEEE) is responsible for creating PoE standards. Click here to learn more about IEEE’s standardization process.

There are currently two PoE standards available. The 802.3af standard supports 15.44 watts of power. But even though 802.3af Powered Sourcing Equipment (PSE) are able to transmit 15.44 watts of power, powered devices (PDs) can only reliably receive 12.95 watts of power due to power dissipation. In 2009, IEEE introduced the higher powered 802.3at standard, also known as PoE+. The standard supports 30 watts of power, but in similar fashion to the 802.3af standard, power dissipation causes powered devices to receive slightly lower amounts of power, specifically 25.5 watts of power.

802.3BT or PoE++

IEEE is currently overseeing yet another higher powered PoE standard. As the utility of PoE expands beyond the networking sector, higher powered PoE will be able to support nurse call systems, point of sale systems, IP turrets used by financial traders, and higher powered IP cameras such as PTZ Cameras, among many other applications.  802.3bt, also known as PoE++, the new standard is expected to be ratified in early 2017, will utilize all four twisted pairs to transmit power. The 802.3bt standard will be able to achieve 49-70 watts of power using this method. The new standard will essentially combine both Mode A and Mode B to achieve the higher voltage. Some sources even site that the standard will be able to supply up to 100 watts of DC power. This newer standard will not only allow for higher power, but will also be able to support 10 Gbps connections. Type A specifies for 60W (50 watts of power) and Type B specifies for about 100 watts of power (approximately 80 watts of power with power dissipation).

PSEs vs. PDs

Before we get any further into understanding the foundations of PoE, it’s important to understand the difference between Power Sourcing Equipment (PSEs) and Powered Devices (PDs). Power sourcing Equipment (PSEs) refers to devices responsible for supplying power to connected devices, such as switches, hubs, and injectors. Powered Devices receive power from PSEs. A few examples include IP cameras, voice-over IP (VoIP), or wireless access points (WAPs) power.

Mode A vs. Mode B

Even though Power over Ethernet is relatively simple to deploy, network administrators need to know the difference between common PoE terms such as compliant vs compatible devices and Mode A vs Mode B power transmission methods. This infographic will help you avoid common PoE caveats that can lead to incompatible connections.    

PoE Use Cases

PoE devices oftentimes use different power pinout pairs to relay power. These different methods are known as Mode A or Mode B. Mode A utilizes data pin pairs 1-2 and 3-6 to transmit and receive data and power, leaving pinout pairs 4-5 and 7-8 unused.

Units that utilize Mode A are sometimes referred to as end-span units.  Mode B on the other hand, leaves no data pairs unused. This is the reason why pins 4-5 and 7-8 are sometimes referred to as the spare pairs, or phantom pairs. When operating in Mode B, all data pairs are used. Mode B sends data using pin outs 1-2 and 3-6.  Power is sent using data pin pairs 4-5 and 7-8. Units that utilize mode B are also referred to as Midspan devices.

The 802.3at standard utilizes pin outs 1-2 and 3-6 to transmit data and power when utilizing Mode A.  The remaining pins are utilized to transmit data. Mode B utilizes pairs 5-4 and 8-7 to transmit both data and power. The remaining pins are used to transmit data.

Though the differences are minimal, it’s an important attribute to consider when deploying devices. Disregarding which power pins are used to transfer and receive power can lead to non-functioning connections.

Endspan PSEs vs. Midspan PSEs

The terms Endspan and Midspan can also be used to indicate which pinouts are used to send and receive power. But Endspan PSEs and Midspan PSEs can also take on a more literal meaning. Midspan PSE’s can oftentimes be characterized as “intermediary devices” deployed between a non-PoE capable PSe with a PoE-capable powered device. Examples of Midspan PoE’s include power injectors or power hubs”.  Endspan devices, on the other hand, can refer to a main PSE in a network such as a switch.

what is PoE infographic

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What is the difference between compatible PoE Devices and Compliant PoE Devices?

What exactly is the difference between PoE-compatible powered devices and PoE-compliant powered devices? Be careful, these two terms are not synonymous.

Though compliant devices are IEEE-certified, compliancy indicates different attributes for Powered Devices and Power Sourcing Equipment. In order for a compliant powered device to be considered compliant, a Powered Device must have the ability to send and receive power using both Modes A and Mode B. But compliancy standards for PSEs do not require the support of both modes. Consequently, some compliant PoE PSEs only support Mode A, some PSEs only support Mode B, while others support both Mode A and Mode B.

PoE-compatible units do not adhere to IEEE standards. However, PoE-compatible units are reliable alternatives that require installers to ensure that the correct Modes are utilized for their networks. PoE compatible PDs for example, most likely support only Mode B, but supported modes vary upon manufacturer. Compliant powered devices on the hand, guarantee that powered devices support Mode A and Mode B power modes.

There is no guarantee that compliant Power Sourcing Equipment will support both power modes.

Similarly, PoE-compatible PSEs such as injectors, can support either modes, but there is no guarantee that it will support both modes. Network installers and system integrators will need to check specification data sheets to verify that their prospective units meet the power modes their network utilizes.

Different PoE Class Types


To prevent over-powering a powered device which can shorten the lifespan of a unit, IEEE compliant PDs that rely on PoE are classified into different classes. PoE classes ensure efficient power distribution by specifying the amount of power that a PD will require. PDs that require less power than the lowest PoE standard receive a low-ranking power classification and allows the PSE to allocate the surplus amount of power to other connected devices. Low-power powered devices require smaller cooling switches “as the lower wattage output will not generate as much heat”. Passive PoE adapters on the other hand, always relay the same amount of power at all times. These units are usually described as ‘non-standard’.

 Different PoE class types help effectively negotiate power between a PSE and PD. The following chart indicates the amount of power allocated to different class types in both the 802.3af and 802.3at standard.

What are the different PoE use-cases?

PoE facilitates the deployment of powered devices in several scenarios. The following are just a few sample use-cases for PoE.                 

PoE Use Cases

IP Surveillance in an Enterprise Building

Outdoor IP cameras give system integrators the ability to deploy cameras around a multi-story enterprise building where electrical circuitry may be absent.

VoIP in an Office Environment

Businesses seeking to save on wired telephone services switch to VoIP phone systems.  

Access Points in a Campus

PoE-capable wireless access points make it simple to disregard the placement of electrical circuitry, and place wireless access points anywhere on a campus.

Allotting Sufficient PoE Power to Your Network


Though PoE is a plug-and-play technology, it’s important for network administrators and system administrators to seek for PSEs (such as switches) with sufficient PoE budget to be able to allocate power to the desired amount of connected powered devices.  

The sum total of PoE power required by connected powered devices must not surpass the total amount of the POE budget specified on a PSE.

For example, the GSD-808HP Desktop Gigabit Switch is an 802.3at PoE compliant PSE that boasts a Total PoE Power Budget of 130 Watts. The unit supports both 802.3af and 802.3at devices. However, if used at full capacity, the unit can only reliably relay 16.25 watts of power per port (130 watts total PoE budget divided by the number of ports). Therefore, though the unit is 802.3at compliant, network administrators should refrain from assuming that the unit can support 8 802.3at Powered Devices. In actuality, the 802.3at compliant device can support 4 802.3at powered devices if used at full capacity. To calculate the amount of 802.3at devices the unit can support, simply divide the Total PoE Budget (130 watts) by 30 watts. The 4.33 figure can be rounded down to calculate the amount of 802.3at units that this particular PSE can support.

Be sure to grab and bookmark our nifty PoE calculator to avoid doing the math!

Free PoE Calculator

II. Determining the Best PoE Units for Your Network

There are a range of PoE equipment available for a variety of networking environments. Industrial PoE units for example, are made to withstand the extreme temperature demands characteristic of industrial environments. Outdoor PoE gear oftentimes comes enclosed in a protective encasement to protect against the elements. Network installers will also need to ensure that their Power Sourcing Equipment allots for a sufficient PoE power budget to support the desired amount of Power Devices.

PoE Switches

Managed and unmanaged PoE Switches come with a variety of different interface options. Though unmanaged switches offer a simple plug-and-play installation, managed PoE switches offer additional beneficial configuration options for networks.

Best desktop switch

8-Port Desktop Gigabit Switch

The GSD-808HP is an 802.3at compliant PoE Switch with 8 PoE interfaces. This unit is ideal for small-scale networks, with a total power budget of 130 watts.

best 24 Port PoE Switch

24-Port 802.3at Gigabit Switch

The WGSW-2620HP4 is a managed PoE switch with SFP ports. With a total PoE budget of 440 Watts, this unit is ideal for mid to large-scale networks.

PoE Injectors

PoE injectors are mid-span devices commonly deployed between a non-PoE capable Switch and a PoE-capable PD such as a PoE IP camera. PoE injectors add or inject power to a network cable to ensure that a connected powered device can receive power and operate without a connected DC power supply.

Best gigabit injector

Single-Port PoE Injector

The VX-Pi100 is an 802.3af compatible unit that can power connected devices such as Access Points, VoIP phones, IP cameras and HDMI extenders.

Similarly, the VX-Pi1000GB provides the same function as the VX-Pi100, but can support gigabit speeds.

For larger-scale deployments, multi-port PoE injector hubs, also known as PoE hubs, perform the function of multiple PoE injectors.

Best PoE Hub

24-Port Multi-Port Gigabit Hub

The HPOE-2400G is an IEEE 802.3at PoE injector hub with a total PoE Budget of 720 watts.

The HPOE-460 is another example of an injector hub but in a smaller form factor. The High Power over Ethernet (PoE) injector hub features 4 gigabit interfaces and a PoE power budget of 120 watts.

PoE Extenders

PoE Ethernet extenders extend PoE network connections using coaxial wiring, twisted pair, or Even UTP cabling.  These units allow network installers to bypass the 100 meter Ethernet limitation and leverage the flexibility of PoE.

best gigabit extender

Gigabit PoE Extender

The VX-PI1000EX is a single-port Gigabit PoE Extender.

best coax extender

Local Powered POE Extender over Coaxial Kit

The VX-160COAX kit is a Coaxial KiT

UTP PoE Extenders

best utp extenders

1-Port Long Reach PoE over UTP PoE Extenders

The LRP-101U-KIT is a 1-Port Long Reach POE over UTP Extender Kit that can transmit PoE power up to 500 meters using 4-par UTP wiring or up to 300 meters using 1-pair telephone wiring.

What is a Power over Ethernet Splitter?

In contrast to a Power over Ethernet Injector, which makes a non-PoE PSD compatible with a PoE-capable PD, a PoE splitter will perform the opposite function of a PoE splitter. A PoE splitter is a PoE device that takes a PoE capable PSD unit and splits data and Power into two separate interfaces

best gigabit splitter

Gigabit PoE Splitter

Industrial PoE Equipment

Industrial PoE equipment comes with stringent standards to ensure operation in extreme industrial conditions. PoE industrial equipment must have the capacity to protect against electrical decoupling, especially in electrically demanding environments such as electrical substations. PoE industrial equipment, sometimes described as Hardened, supports extreme operating temperatures, and additional optional measures of protection including dustproof, weatherproof, and waterproof attributes.

Industrial PoE Injectors

best industrial injector

One-Port Industrial PoE Injector

The INJ-IG01-PH is an 802.3af/at Gigabit Ethernet PoE+ Injector that can withstand -40 to 75°C temperatures.

Industrial PoE Switches

best poe industrial switch

4 Port PoE+ Managed Ethernet Switch with 2 100/1000Base-X SFP Slots

The IFS-402GSM-4PH24 is an industrial PoE Switch with 4 Fast Ethernet interfaces and 2 100/1000Base-X SFP interfaces with operating temperatures between -10 to 60 °C.

Energy Efficient PoE (EEPoE)

Many PoE units come with advanced PoE management features that allow for energy-efficient networks. Features such as PoE Schedule confines power feeding times to pre-scheduled time slots.

III. The Future of PoE and IoT

PoE allows for flexible network designs that are simple to deploy. The practicality of PoE wiring leaves future application possibilities for PoE open for exploration. In the wake of the Internet of Things (IoT) revolution, PoE is positioned to gain traction. “As an increasing amount of objects and sensors connect to the internet, PoE has the potential of becoming as integral to an infrastructure as electrical circuitry.”[1] This prospect seems more viable, especially with the ratification of the 802.3bt standard which promises higher PoE power.

PoE Lighting

One such application that is quickly gaining popularity is PoE lighting. Network administrators can use PoE to provide power to energy-efficient LED bulbs using standard network cabling like Cat5e or Cat6 wiring. LED lights have an average life-span of about 50,000 hours and utilize only 6-8 watts of power per bulb. With a PSE with sufficient amount of PoE budget, network administers can deploy PoE lighting with a low amount of investment. In addition, standard networking cables are also a cost-effective alternative to the traditional electrical conduit used for wiring. PoE lighting gives users access to smart lighting using a simple internet connection.  PoE lighting gives users the ability to remotely control their lighting systems via a mobile client device or a web browser. LED light installations will not require professional electrical installers. In fact, IT personnel are positioned as the new electricians of the future. PoE LED lighting allows office users to endlessly customize their work environments with flexible lighting.

PoE Lighting

PoE in Co-Working Spaces

PoE could potentially become the source of electrical power in both homes and enterprises. PoE’s versatility could especially be useful in co-working spaces that are commonly found in the startup sphere. These co-working spaces are oftentimes occupied by freelancers and independent contractors where office arrangements are never permanent. As PoE adopts more applications beyond computer networking, PoE can potentially act as a shifting power source that new users can easily modify without the help of professional installers.

best poe adapters

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