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What is Power over Ethernet (PoE)?

Power over Ethernet (PoE) is the process of sending electrical power and data over copper wire.

The combination of data transmission along with power supplying hardware onto the same RJ45 Ethernet connector allows for the transmission of power over the network cabling. PoE networks can source power at the network switch side or at a PoE injector to add power to an existing data line.

How Does Power over Ethernet (PoE) Work?

Power over Ethernet is a process where devices known as power sourcing equipment (PSE) provide a direct current (DC) voltage over a standard Ethernet cable to another connected device known as a powered device (PD). This allows for the powering of devices without the need for a local power source at the device location or having to run a separate cable for power.

History of Power over Ethernet

Before Ethernet communications, devices like cameras required a signal cable to transmit the image back to a recorder. These devices also required local power supplies to provide power. Because cameras and similar devices are often installed in locations where local power may not be available, companies started running a mix of signal and power cables with a power supply transmitting power from the head end recorder location.

Through further development into signaling and power technologies, cameras started using multi-pair UTP cables, like CAT5, to send a mix of signaling and power. Signaling was sent on one or two of the four pairs of a CAT5 cable, and power transmitted on the remaining two pairs. This helped to simplify installations, as fewer cables were required to accomplish the same task.

When endpoint signaling moved away from analog transmissions to IP, this capability was lost. Then in 2003, Power over Ethernet was created and standardized by the Institute of Electrical and Electronics Engineers (IEEE).

Power Over Ethernet Standards

The Institute of Electrical and Electronics Engineers (IEEE) is the governing body that creates standards for Ethernet and other data communications. The first governing document created for PoE was 802.3AF, which states that compliant Power over Ethernet switches delivers 15.4W of power to guarantee delivery of 12.95W at the endpoint.

What is PoE+?

Improvements to this standard came in the form of 802.3AT, also known as PoE+, which states that Power Sourcing Equipment can provide 30W of power to ensure 25.5W at the endpoint. To guarantee a successful negotiation, both the switch and the endpoint device must be IEEE compliant. However, some device manufacturers have created their own implementations of PoE.

There are three main techniques for transmitting power over Ethernet cabling. These are Mode A (also known as common-mode data pair power), Mode B (spare-pair power), and 4PPoE (4-Pair power). With Mode A the power is provided on the same cable pair as the data pairs used in a 10Base-T or 100Base-TX transmission. With Mode B the spare pairs are used and with 4PPoE all 4-pairs of the Ethernet cable are used for power transmission. Below are the specifics of each mode.


PoE ModeEthernet Cable pairs utilisedPin allocation
Mode AData Pairs. Pins 1, 2 & 3, 6Pins 1, 2 = Positive Voltage (DC+)

Pins 3, 6 = Negative Voltage (DC-)

Mode BSpare Pairs. Pins 4, 5 & 7, 8Pins 4, 5 = DC+

Pins 7, 8 = DC-

4PPoEAll 4 PairsPins 1, 2 & 4, 5 = DC+

Pins 3, 6 & 7, 8 = DC-


These have been standardised by the Institute of Electrical and Electronics Engineers (IEEE) under the Ethernet Standard 802.3. The first being standardised in 2003.


IEEE StandardPoE Mode SupportedYear of Standardisation
802.3afMode A, Mode B2003
802.3atMode A, Mode B2009
802.3btMode A, Mode B, 4PPoE2018


Each IEEE standard depicts how the power is delivered, the voltage (V) supplied, and the wattage (W) available as can be seen in the below table:


IEEE StandardPoE TypeDC Voltage output at PSEPower delivered by PSEVoltage Available at PDWattage Available at PDPoE Mode Supported
802.3afType 1 “PoE”44-57V15.4W37-57V12.95WMode A

Mode B

802.3atType 2


“High PoE”

50-57V30W42.5-57V25.5WMode A

Mode B

802.3btType 3


42.5-57V60W42.5-57V51WMode A

Mode B


802.3btType 4



There are varying names for these PoE standards, as can be seen under the PoE Type heading in the above table but essentially, they all fall under the specified IEEE standards listed.


Power over Ethernet Classes

The Power over Ethernet Class is reserved for powered devices (PD). The class specifies how much power the PD requires to function. There are currently 9 PoE classes ranging from 0 to 8. They are as follows:

ClassUsageWattage required at PD
0Valid for Type 1 (802.3af) devices0.44–12.94W
1Valid for Type 1 (802.3af) devices0.44–3.84W
2Valid for Type 1 (802.3af) devices3.84–6.49W
3Valid for Type 1 (802.3af) devices6.49–12.95W
4Valid for Type 2 (802.3at) devices,
not allowed for 802.3af devices
5Valid for Type 3 (802.3bt) devices40W (4-pair)
6Valid for Type 3 (802.3bt) devices51W (4-pair)
7Valid for Type 4 (802.3bt) devices62W (4-pair)
8Valid for Type 4 (802.3bt) devices71.3W (4-pair)

In most cases, the datasheet of a PD will display the PoE Class of the device or at least the IEEE standard it adheres to in the power, power consumption, or electrical sections.


Advantages of Power Over Ethernet

PoE provides four primary advantages: lower infrastructure costs, fast and simple deployments, improved LAN design, and reduced e-waste.

Endpoint devices require two connections: data and electrical. The data connection allows communication with the network while the electrical connection powers the device. Separately installing both connections is costly and unnecessarily complicated, especially when considering the number and location of the devices across the organisation. Power over Ethernet provides both connections using a single wire.

Many companies will install a PoE switch fabric when modernising from older, analog voice and security systems, or when deploying a new system. PoE switches provide numerous benefits:

  1. Lower infrastructure costs
  2. Fast and simple deployment
  3. Improved LAN design
  4. Less e-waste


Lower Infrastructure Costs

Businesses looking to modernise from analog/digital devices to IP already have the most critical requirement, a proven and reliable LAN infrastructure. This cabling can be leveraged using Power over Ethernet technology to support IP endpoints. Organisations have been doing this for over ten years to ensure simple VoIP and security upgrades.

Companies are saving millions of dollars in network readiness costs while avoiding the unforeseen challenges that come with an enterprise-wide network overhaul. These cost savings are realized through significantly reduced labour, cabling, and construction costs, which are often reallocated into devices and applications to improve return on investment.

The extended reach capabilities significantly reduce IDF closet requirements – including space, power, cooling, and backup power – to reduce cost, network complexity, and to simplify network management. PoE switches are simple to deploy, configure, and manage. Deploying devices across multiple locations is easy, thanks to the repeatable, predictable, and scalable deployment methodology.

Fast and Simple Deployment

Deployments using Power over Ethernet technology are quick and easy, especially when leveraging network infrastructure that is already in the building. Simply install the PoE switch in the MDF closet, connect to the new or existing network cabling, and connect the device at the endpoint location.

Improved LAN Design

Organisations have the freedom to establish/maintain a physically separate Power over Ethernet network, or centrally converge to the core network using a single wire in a highly secure and controlled manner. This applies to both Cloud and on-premise solutions and significantly improves network security and performance. Quality of service is enhanced while ongoing network management is simplified as IT teams continue to manage the core business network while voice/security teams can handle these separate networks.

Additionally, as core business applications and data terminals (employee computers, Wi-Fi access points) continually require more and more bandwidth, network equipment will generally evolve every 3 to 5 years. By physically segmenting your PoE network, you can make changes to your core business network without impacting or disrupting your communication, security, and other systems.

Explore our PoE Injector range HERE

For more information on your PoE network contact the Powertec team today at 1300 769 378 or sales@powertec.com.au 


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