What is Power over Ethernet (PoE)?

Power over Ethernet, or PoE, allows both data and power to be delivered over an Ethernet cable. By eliminating the need for separate electrical wiring, PoE reduces the time, complexity and costs associated with powering a variety of networked devices.
 

PoE technology is commonly used in the following:

• Security cameras
• Wireless access points
• VoIP phones
• IoT sensors
• Building automation systems
• Digital signage

The number of PoE-powered devices continues to grow as organizations adopt smart buildings, IoT networks and intelligent lighting systems.

Types of PoE devices and equipment

Powered Devices (PD) - Any PoE-compliant device that can be powered through its RJ45 network port is referred to as a Powered Device or PD for short. The number of installed PDs is growing at approximately 12% per year, with the scope of applications expanding rapidly in areas such as video-conferencing, smart buildings, sensor networks, point of sale (PoS) and digital signage. Currently, high demand for PoE security cameras from commercial and industrial users is driving market growth. However, PoE LED lightning is expected to boost market adoption thanks to some compelling benefits, including lighting control, integration with other devices, ease of installation and operational cost savings.

Power Sourcing Equipment (PSE) - refers to devices that supply electrical power to connected devices, such as IP cameras, wireless access points, and VoIP phones, through an Ethernet cable. In the context of PoE, PSE is responsible for delivering power and data simultaneously over standard Ethernet cables, eliminating the need for separate power lines.

PoE Extenders – The maximum length of an Ethernet cable is 100 meters (328 ft.) but this can easily be extended using a hub or switch. In PoE applications, an extender is used to "repeat" both the data and power, extending the cable run another 100 meters. This can be done a number of times before power degrades below the requirements of the PD. Ruggedized PoE Extenders are available for industrial and manufacturing applications, such as Eaton's water resistant Gigabit PoE+ Extender (Part Number NPOE-EXT-1G30WP).

PoE Splitters – To power a non-PoE device, a splitter draws power from the Ethernet cable and passes it to the device via its power port.

PoE Injectors - Use a PoE injector (also called a midspan) to add a PoE device to a non-PoE network. This is generally a more cost-effective solution than adding a PoE switch or running AC power to the point of installation. Products like Eaton's PoE+ injector (Part Number NPOE-30W-1G) support 30W of power to a PoE device on a Gigabit network.

Media Converters – Transparently convert fiber to copper and provide power to PoE-compliant devices such as IP cameras, VoIP phones and wireless access points. A media converter is a type of PSE (it requires an AC power source) and is typically used when extending a data network beyond the limits of Ethernet.

Power-over-Ethernet Standards

The Institute of Electrical and Electronic Engineers (IEEE) released the first Power over Ethernet (PoE) standard in 2003, establishing common guidelines for the delivery of power over an Ethernet network. PoE provided compelling benefits over conventional AC power, including easy installation, increased safety, reduced capital expenditures and lower operating costs, paving the way for rapid adoption.

* The difference between the power provided by the PSE and the power received by the PD is power lost in transmission in the form of heat.

The latest standard, IEEE 802.3bt, enables higher-power devices such as:

• PTZ security cameras
• LED lighting systems
• thin clients
• building automation controllers

These higher power levels are achieved by utilizing all four twisted pairs in the Ethernet cable.

How PoE Works

PoE systems use an intelligent process to safely deliver power to connected devices.

Signature Detection

PoE switches periodically check their ports to determine whether a PoE device is connected. A low voltage signal detects the device signature without damaging non-PoE equipment.

Power Classification

After detecting a powered device, the switch determines how much power the device requires.

PoE standards define several power classes, allowing switches to allocate power appropriately.

Maintain Power Signature (MPS)

Even when devices enter low-power modes, they must signal that they are still connected. This signal, called the Maintain Power Signature, prevents the switch from shutting off power.

PoE Power Budget

Every PoE switch has a power budget, which is the maximum total power it can deliver across all ports.

Modern PoE standards include features like autoclass, which dynamically adjusts power allocation to optimize energy usage and allow more devices to connect.

UL Limited Power (LP) Cable Certification

Higher-power PoE standards generate additional heat, especially in large cable bundles.

To address this, Underwriters Laboratories introduced Limited Power (LP) certification for Ethernet cables.

LP-rated cables are tested for safe operation in:

• high-temperature environments
• enclosed conduits
• dense cable bundles

Look for cable markings such as CMR-LP when installing higher-power PoE networks.

What is a PoE Switch?

A PoE switch combines traditional network switching with power delivery over Ethernet ports.

In addition to forwarding network traffic, a PoE switch provides electrical power directly to connected devices.

PoE switches are commonly connected to a UPS to ensure network devices remain operational during power outages.