May 13, 2020 by Emmanuel Ikimi
First introduced in 1997 by PowerDsine (a semiconductor and systems company ultimately acquired by Microsemi), Power over Ethernet (PoE) is today one of the most efficient, cost-effective, and scalable cabling standards in the electronics industry.
This article will discuss the operation, types and specifications, advantages, and key applications of PoE technology.
PoE is a relatively new technology for simultaneously delivering data and electric power over twisted-pair Ethernet cables. By eliminating the need for separate cables for power and data, PoE allows engineers to achieve greater flexibility and scalability in their designs.
Standard Ethernet cables like Cat 5e and Cat 6 with RJ45 connectors are readily compatible with PoE switches. However, Cat 6 cables are often selected as their larger-than-average conductor diameters help to minimise the surface resistance and temperature rise, collectively resulting in power loss.
Cat 6 PoE+ cables connected to a patch panel.
Currently, there are several PoE types available, with varying power levels. The three recognised versions are PoE, PoE+, and PoE++.
The original PoE version (aka IEEE 802.3af., Legacy PoE, or PoE Type 1) was first introduced in 2003. PoE utilises two Ethernet cable pairs for shuttling up to 15.4W DC per port—although, due to power dissipation in the cable, they, in fact, achieve a power delivery (PD) of 12.95W to the device. PoE is widely used in Voice over Internet Protocol (VoIP) phones, static surveillance cameras that have no pan-tilt-zoom (PTZ) functionality, and wireless access points with up to two antennas.
The PoE+ specification (aka IEEE 802.3at or PoE Type 2) emerged in 2009. It is an upgraded version of PoE that is suitable for applications with high power requirements. Similarly to legacy PoE, PoE+ utilises two Ethernet cable pairs, but with a PD of 30W DC per port (48VDC at 0.63A) and 25.5W of power delivered to the device.
In addition to this,PoE+ is also backwards compatible with legacy PoE, meaning that only a PoE+ switch is required for use with existing cables. With the higher power capacity, PoE+ is suitable for a wide range of electronic devices that use Ethernet cables, including wireless access points (with up to six antennas), high-speed communications equipment, and PTZ cameras.
PoE++ (aka IEEE 802.3bt) is an upgrade to PoE+ that enables data transmission with power delivery up to 100W DC via 4-pair Ethernet cables. There are two types:
IEEE 802.3bt Type 3 (aka ‘Universal PoE’ or UPoE) with 60W maximum power per port and 51W power delivery to the device
IEEE 802.3bt Type 4 with 100W maximum power per port and 71.3W power delivery to the device
PoE++ Type 3 is suitable for applications such as multi-radio wireless access points, and electrical equipment used in video conferencing. PoE++ Type 4 meets the high-power requirements of television sets, laptops, digital signage equipment, and the incoming 5G systems.
A close-up of ethernet cables connected to a PCI Express network adapter.
There are several ways to integrate PoE functionality in electronic applications, including the following two examples.
A PoE switch is a kind of network switch for enabling PoE functionality in existing systems. To use a PoE switch, an Ethernet cable is connected from its LAN port to the powered device (e.g., a security camera), followed by connecting a power cable to a power outlet and the PoE switch. The PoE switch provides power and data via several ports for all connected devices.
A PoE injector (aka a ‘Midspan’) is a device for adding electrical power delivery to a data cable connection. PoE injectors are usually used alongside existing network switches without PoE functionality. To use a PoE injector, both devices must be powered on and connected using an Ethernet cable, followed by connecting powered devices such as VoIP phones or PTZ cameras.
Power over Ethernet (be it PoE, PoE+, or PoE++) offers the following benefits in electronic applications and more:
Transmitting data and electric power over a single cable reduces wiring and installation costs for separate power outlets.
PoE is easy to install and readily integrated into conventional wiring
PoE helps to simplify wiring in applications up to 100 metres
Newer PoE installations are backwards compatible with older versions
Ethernet cables connected to a PoE network switch.
Smart buildings incorporate internet-connected devices, sensors, and software to monitor and control appliances and security/surveillance hardware. PoE+/PoE++ provides a robust solution for deploying network cables with enhanced scalability (particularly in smart homes and smart factories), all while eliminating the need for power outlets.
A significant Power over Ethernet application is in remote and automated LED lighting, as the PoE-powered light-emitting diodes automatically reduce or increase in luminous intensity depending on ambient lighting conditions (or switch on or off when factory workers are away to conserve power).
According to a 3rd Watch News market report, the global PoE switch market will experience sustained growth over the next six years due to both the competition from major manufacturers and the increase in relevant applications for the technology.
PoE provides unparalleled power delivery, robustness, and scalability in a broad range of applications. It also allows users to save huge costs on cabling as the data and power are delivered over the same cable.
With emerging technologies like 5G devices and existing applications in networking, home automation, smart factories, and more, Power over Ethernet usage will rapidly expand to meet demands for high-power delivery in electronic devices and equipment.
