Power over Ethernet Explained

What is Power over Ethernet?

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. Power over Ethernet 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 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.

Power over Ethernet Evolution

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 Power over Ethernet was 802.3AF, which states that compliant Power over Ethernet switches deliver 15.4W of power to guarantee a delivery of 12.95W at the endpoint.

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 Power over Ethernet.

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 Mode Ethernet Cable pairs utilised Pin allocation
Mode A Data Pairs. Pins 1, 2 & 3, 6 Pins 1, 2 = Positive Voltage (DC+)

Pins 3, 6 = Negative Voltage (DC-)

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

Pins 7, 8 = DC-

4PPoE All 4 Pairs Pins 1, 2 & 4, 5 = DC+

Pins 3, 6 & 7, 8 = DC-

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

IEEE Standard PoE Mode Supported Year of Standardisation
802.3af Mode A, Mode B 2003
802.3at Mode A, Mode B 2009
802.3bt Mode A, Mode B, 4PPoE 2018

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 Standard PoE Type DC Voltage output at PSE Power delivered by PSE Voltage Available at PD Wattage Available at PD PoE Mode Supported
802.3af Type 1 “PoE” 44-57V 15.4W 37-57V 12.95W Mode A

Mode B

802.3at Type 2

“PoE+”

“High PoE”

50-57V 30W 42.5-57V 25.5W Mode A

Mode B

802.3bt Type 3

“PoE++”

42.5-57V 60W 42.5-57V 51W Mode A

Mode B

4PPoE

802.3bt Type 4

“PoE++”

41.1-57V 100W 41.1-57V 71W 4PPoE

There are varying names for these Power over Ethernet 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 Class

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:

Class Usage Wattage required at PD
0 Valid for Type 1 (802.3af) devices 0.44–12.94W
1 Valid for Type 1 (802.3af) devices 0.44–3.84W
2 Valid for Type 1 (802.3af) devices 3.84–6.49W
3 Valid for Type 1 (802.3af) devices 6.49–12.95W
4 Valid for Type 2 (802.3at) devices,
not allowed for 802.3af devices
12.95–25.50W
5 Valid for Type 3 (802.3bt) devices 40W (4-pair)
6 Valid for Type 3 (802.3bt) devices 51W (4-pair)
7 Valid for Type 4 (802.3bt) devices 62W (4-pair)
8 Valid for Type 4 (802.3bt) devices 71.3W (4-pair)

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

Maximum Distance for Power Over Ethernet

Over the past 30 years, Power over Ethernet technology has seen incredible innovation. Initially, one of the primary downsides of Power over Ethernet was the limited reach of 328ft (100m). However, new PoE innovations, like those from NVT Phybridge, are pushing the limits of Power over Ethernet transmission over several cable types. For example, the NVT Phybridge CLEER24 is an enterprise-grade 24-port PoE switch that delivers power and data up to 6,000ft (1,830) over a single Coax cable. That’s 18 times farther than a standard reach Power over Ethernet switch.

NVT Phybridge Power over Ethernet

The enterprise-grade 24 and 48-port PoLRE® switches deliver power and data over a single pair of UTP cable (also known as Category 3 cable or voice-grade cable used for telephone wiring) with up to 1,200ft (365m) reach. The NVT Phybridge FLEX24 switch delivers power and data over 2 or 4-pairs of UTP cable (Category 5/6 cable) with up to 2,000ft (610m) reach.

See how our PoE switch performance compares

Advantages of Power Over Ethernet

Power over Ethernet 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 organization. Power over Ethernet provides both connections using a single wire.

Many companies will install a Power over Ethernet switch fabric when modernizing from older, analog voice and security systems, or when deploying a new system. NVT Phybridge PoE switches provide numerous benefits:

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

Lower Infrastructure Costs

Businesses looking to modernize from analog/digital devices to IP already have the most critical requirement, a proven and reliable LAN infrastructure. This cabling can be leveraged using NVT Phybridge Power over Ethernet technology to support IP endpoints. Organizations 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 labor, 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. NVT Phybridge 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

Organizations 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.

Less E-Waste

By repurposing existing infrastructure and reducing/eliminating IDF closet requirements, organizations are significantly reducing the environmental impact of their digital transformations. Far less cabling and equipment e-waste is produced. NVT Phybridge Power over Ethernet switches are built with PowerWISE technology to ensure low energy consumption, power redundancy, and hot-swappable power supplies.

Related Resources

Managed vs. Unmanaged Switches

Power over Ethernet Performance Metrics Explained

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