What Is Power over Ethernet (PoE) and How Does It Work?

Power over Ethernet, usually called PoE, is a technology that sends electrical power and data through the same Ethernet cable. Instead of running separate power and network connections to a device, PoE can provide both with one cable.

PoE has been around for years. It was first widely used to power devices like office phones, wireless access points and security cameras. But the technology has changed quite a bit. Newer PoE standards can provide much more power than the early versions could.

That has opened the door to a much wider range of uses. Today, Power over Ethernet can power LED PoE lighting, sensors, automated shades, displays and other devices found throughout commercial buildings.

For building owners and facility teams, this changes what the network can do. Ethernet is no longer just a way to move data from one device to another. It can also become part of the building’s power and control infrastructure.

How Does Power over Ethernet Work?

A PoE connection has two basic sides: the PoE equipment supplying the power and the device receiving it.

The equipment supplying power is called Power Sourcing Equipment, or PSE. A Cisco network switch is one of the most common examples. It provides a network connection while also sending DC power through the Ethernet cable.

On the other end is the Powered Device, or PD. As the name suggests, this is the device using the power. A security camera, wireless access point, sensor or lighting controller could all be powered devices.

One of the useful features of standards-based PoE is that the switch doesn’t simply send full power down every connected cable.

The equipment first checks to see whether the connected device is designed to accept PoE. It can then determine how much power that device needs based on the PoE standard and power class being used.

This process helps PoE safely power many different types of devices from the same network infrastructure.

What Equipment Is Used in a PoE System?

A PoE system can be fairly simple. For example, a PoE switch might connect directly to a security camera. Commercial building systems can be much larger. Depending on the application, a PoE system may include:

• PoE network switches
• Ethernet cabling
• Patch panels
• Powered devices
• PoE nodes and controllers
• Injectors or splitters
• Occupancy and environmental sensors
• Wall switches and other user controls
• Network and building management software

In an intelligent building, hundreds or even thousands of connected devices may operate across the network. Those connections can do more than provide power. They also give devices a way to communicate and share information with other building systems.

How Much Power Can PoE Deliver?

PoE has become much more useful because of the amount of power it can now provide.

There are four main PoE types:

The original PoE standard provided up to 15.4 watts from the power source. That was plenty for devices like phones and some security cameras.

PoE+ increased that to 30 watts. Later, the IEEE 802.3bt standard increased available power again, first to 60 watts and then to as much as 90 watts.

Not all of that power reaches the device. Some is lost as electricity travels through the cable. That’s why you’ll sometimes see one power number listed for the PSE and a slightly lower number for the device itself.

The jump to higher-power PoE was especially important for commercial buildings. It made it possible to use network power for equipment that earlier PoE systems couldn’t support.

For a closer look at these standards, see PoE vs. PoE+ vs. PoE++: What’s the Difference?

How Far Can Power over Ethernet Run?

For a standard Ethernet connection, the maximum PoE distance per channel is generally 100 meters, or about 328 feet. That typically includes up to 90 meters of permanent cabling plus the patch cables used at each end. Power adds another consideration.

As electricity travels through an Ethernet cable, some power is lost along the way. How much is lost can depend on the type of cable, conductor size, distance, temperature and how much power the connected device needs. This becomes more important with higher-power PoE applications. For buildings where devices need to be located farther away, designers may need to use additional network equipment or another method of distributing power.

We cover that subject in more detail in How Far Can Power over Ethernet Run?

What Is Power over Ethernet Used For?

You’ve probably used devices powered by PoE without realizing it. The technology is common in offices, schools, hospitals, hotels and other commercial buildings. Some of the most common applications include:

Wireless Access Points

Wireless access points are often mounted on ceilings or in other locations where an electrical outlet would be inconvenient. PoE lets the same cable provide the network connection and the power needed to run the access point.

Security Cameras

IP security cameras are another common use for PoE. One Ethernet cable can provide power while also carrying video and other data back to the network.

VoIP Phones

Office phones were one of the early uses for PoE. Instead of plugging every phone into a separate power adapter, the network can power the phones directly.

Building Sensors

Modern buildings use sensors to measure occupancy, temperature, air quality and other conditions. PoE can power these sensors while also giving them a network connection. That allows the information they collect to be used by other building systems.

LED Lighting

LED lighting is a particularly interesting use for higher-power PoE. A PoE lighting system can use Ethernet infrastructure to provide power and control to lighting throughout a building. Because the lights are connected to the network, they can also work with sensors, schedules and building management software.

Automated Shades

PoE can also be used to power motors and controls for automated window shades. Shades can then work with lighting controls, occupancy information or other building systems.

Displays and Other Connected Devices

Room scheduling displays, touchscreens, digital signage and other devices may also be powered through Ethernet, depending on how much power they require.

How Does PoE Lighting Work?

PoE lighting uses Ethernet infrastructure to power and control LED lighting. In a traditional lighting system, AC electrical power is distributed to lighting loads throughout the building. With PoE lighting, network equipment can provide DC power that is then used by the LED fixtures.

Depending on the system design, intelligent Inspextor nodes or PoE controllers may sit between the network switch and the fixtures. The real advantage is that the connection isn’t only providing power. It can also provide control and communication.

Lights can be controlled individually or in groups. Occupancy sensors can tell the system whether a room is being used. Schedules can automatically adjust lighting throughout the day. Data from the system can also be shared with other building platforms. This turns lighting into part of the building network rather than a stand-alone electrical system.

For a deeper look at the technology, see What Is PoE Lighting and How Does It Work?

What Are the Benefits of Power over Ethernet?

There isn’t one single reason to use PoE. The benefits range from facility management cost savings to convenience. Its value comes from combining several functions into the same infrastructure.

Power and Data Over One Cable

A single Ethernet cable can provide both power and a network connection. That can reduce the need for separate infrastructure at each connected device.

Centralized Power

PoE power generally comes from centralized network equipment instead of a separate AC connection at every endpoint. Centralized equipment can also be connected to backup power systems when the project requires it.

More Control

Because PoE devices are connected to the network, they can often be monitored and controlled individually. For a lighting system, that might mean controlling a single fixture, a room or an entire floor through software.

Useful Building Data

Connected devices can also provide information. Occupancy sensors can show how spaces are being used. Environmental sensors can track conditions such as temperature or air quality. Lighting and control systems can provide information about equipment operation. That data can be useful for facility management, building automation and space planning.

Flexibility

Buildings change over time. Offices are reconfigured, tenants move and new technology is added. Structured cabling and network-based controls can make some of those changes easier because devices aren’t always tied to traditional electrical control methods.

The exact benefits depend on the project, but this combination of power, data and control is one of the main reasons PoE has become important in intelligent buildings.

Is Power over Ethernet Safe?

Yes, when properly designed and installed, standards-based PoE is designed to deliver power safely to compatible devices.

The network equipment checks the connected device before supplying PoE power. This helps prevent power from simply being sent to equipment that isn’t designed to receive it. That doesn’t mean installation requirements can be ignored.

Higher-power PoE systems need the right cabling and proper system design. Cable bundles, heat, distance and power requirements can all affect an installation. Projects must also follow applicable electrical, building and fire codes.

Is Power over Ethernet Considered Low Voltage?

PoE is commonly described as a low-voltage or limited-energy technology because it operates very differently from the traditional AC electrical systems found in buildings.

However, “low voltage” can have a specific meaning under electrical codes and licensing rules. Requirements can also vary depending on where a project is located and what is being installed.

That distinction matters when deciding who can install the cabling, whether permits are required and what installation methods must be followed.

Those questions are covered more closely in Is Power over Ethernet Considered Low Voltage? and Does PoE Require an Electrician?

How Does PoE Fit Into an Intelligent Building?

This is where Power over Ethernet becomes especially useful for modern commercial buildings.

Traditionally, many building systems operated separately. Lighting had one set of controls. HVAC had another. Security, shades and sensors might each operate on their own systems.

PoE gives more of these devices a way to connect through the building’s network infrastructure.

A sensor can detect that a conference room is empty. The lighting system can respond. Automated shades can adjust based on a control strategy. Building software can collect information from connected devices and give facility teams a better picture of how spaces are being used.

Not every building system needs to run on PoE. But as more devices become connected, the network can play a much larger role in how a building operates.

Power over Ethernet Is More Than a Way to Power Network Devices

PoE started as a practical way to power devices such as phones, cameras and wireless access points without installing a separate electrical connection.

Higher-power PoE has taken the idea much further.

Today, Power over Ethernet can support lighting, sensors, controls, automated shades and other systems throughout a commercial building. The same infrastructure can deliver power, carry data and provide a connection between devices and building software.

That makes PoE more than a networking convenience. It can become an important part of the infrastructure behind a connected, intelligent building.