Blog: The value of Power-over-Ethernet (PoE)

April 09, 2021 // By Mark Patrick
Blog: The value of Power-over-Ethernet (PoE)
Mark Patrick of Mouser Electronics looks at the benefits of delivering data and power together in an industrial context with power-over-ethernet (PoE) standards

Power-over-Ethernet (PoE) comes into its own with IIoT and Industry 4.0 applications as the PoE standard allows unused wires or data lines within an existing Ethernet cabling system to power sensors and actuators.

In the previous two blogs, we discussed the macro considerations for power within industrial settings. We highlighted how motivation for energy and process efficiency is changing the landscape of the factory floor. The adoption of Industry 4.0 and IIoT is pushing data storage away from local servers toward the cloud at one extreme and data processing toward the sensors and actuators at the other, utilising 'edge' computing for fast, localised decision making.

Mixing power and data

Powering the 'edge,' where sensors may feature a microcontroller, memory and a wireless or wired data link, requires access to a supply. For wireless actuators and sensors, the options are battery, AC-DC adapter, or perhaps energy harvesting. However, wired Ethernet data connections are often employed to supply power as they are ubiquitous. The reasons are not just historical; wireless is inherently less secure, and most devices work in the license-exempt bands. There can be congestion, packet delays, and stability issues, especially with multiples crowded in an electrically noisy industrial environment.

The development of Power over Ethernet (PoE)

The Ethernet standard has existed since 1973, though initially a coaxial cable-based system, differential signals on twisted pair wires are now used extensively. Gigabit/s communications often use four twisted pairs. Lower speeds use only two twisted pairs - typical for industrial use to process data from sensors. PoE can use existing Ethernet installations in areas lacking AC-DC power outlets. Additionally, it can be installed without reliance on qualified electricians.

IEEE 802.3af standard

Under the 802.3af standard (IEEE 802.3 – 2003), unused pairs could deliver power; known as mode B or Midspan. The PoE midspan method uses PoE Injectors to add PoE to your networks without adding or replacing your existing non-PoE switches. These are intelligent


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