edVirtus Reference

What Is Power over Ethernet?

How Does Power over Ethernet Supply Electrical Power Through a Network Cable?

Power over Ethernet (PoE) is a technology that enables both electrical power and Ethernet data to be transmitted through a single twisted-pair Ethernet cable. By eliminating the need for a separate power supply at the connected device, PoE simplifies installation, reduces cabling costs, and allows network devices to be installed in locations where conventional power outlets may not be readily available.

The basic principle is straightforward. A Power Sourcing Equipment (PSE), such as a PoE-enabled Ethernet switch or injector, supplies direct current (DC) power onto the Ethernet cable. A compatible Powered Device (PD) detects the presence of PoE, negotiates the required power level, and safely draws electrical power while simultaneously exchanging Ethernet data over the same cable. Standardised detection and classification procedures ensure that power is applied only to compatible devices.

A useful analogy is a railway line that carries both passengers and freight on the same track. Instead of constructing separate routes for each purpose, both services share the same infrastructure. Similarly, PoE allows electrical power and digital communication to share a single network cable.

PoE is widely used to power devices such as wireless access points, IP telephones, IP security cameras, network intercoms, building access controllers, IoT sensors, and LED lighting systems. Because power is delivered centrally from the network equipment, devices can continue operating from an uninterruptible power supply (UPS) connected to the network switch during mains power interruptions.

Several IEEE standards define PoE capabilities. IEEE 802.3af supplies up to approximately 15.4 W per port, IEEE 802.3at (PoE+) increases this to approximately 30 W, while IEEE 802.3bt (PoE++ or 4PPoE) supports up to approximately 90 W for higher-power devices such as pan-tilt-zoom cameras, digital displays, and advanced wireless access points.

It is important to distinguish Power over Ethernet from a conventional Ethernet connection. Standard Ethernet carries only data, requiring each device to have its own local power supply. PoE combines both services on the same cable while remaining fully compatible with normal Ethernet communication standards. It also differs from proprietary power injection methods that predated the IEEE standards and were often incompatible between manufacturers.

Today, Power over Ethernet has become a standard feature of modern enterprise networking. Its ability to reduce installation complexity, centralise power management, and support flexible deployment has made PoE an essential technology for commercial buildings, industrial automation, security systems, wireless networking, and smart-building infrastructure. As connected devices continue to proliferate, PoE remains one of the most practical and economical methods of powering network equipment.