The professional organization Institute of Electrical and Electronics Engineers (IEEE) developed the standard for PoE and it is listed as IEEE 802.3af. This standard defines the power requirements and network communication that can pass through Ethernet cables. In a PoE-based system, the Ethernet cable has four twisted-pairs of wires. The twisted-pairs can carry power, data transmission, or both.
Components of a PoE System
The two components of a PoE system are the power sourcing equipment (PSE) that provides power for the power devices (PD). Commonly, a PSE is a PoE-enabled Network Switch that provides both power and data management for PDs. A few typical PDs include Internet Protocol (IP) cameras, Voice over Internet Protocol (VoIP) phones, security card readers, laptops, and particle counters.
IEEE 802.3af System vs. IEEE 802.3at System
In an IEEE 802.3af system (low power), the power is supplied using two pairs of wires – at pins 1 & 2 and pins 3 & 6. In an IEEE 802.3at system (high power), the power is supplied using all four pairs of wires, with the addition of pins 4 & 5 and pins 7 & 8. Table 1 describes the differences between these IEEE standards.
A few benefits that PoE currently offers are listed below:
- A single Category 5 (Cat5), Cat5e, or Cat6 cable provides both power and data communications.
- Installing a single cable requires less time, cost, and resources.
- Devices can be installed in remote locations where power outlets are not available.
- The PSE connected to a Universal Power Supply (UPS) provides constant power and overload protection to all connected PDs.
- Since the PSE supplies power and communications, all PDs can be controlled, and the entire system can be quickly updated, repaired, or receive firmware upgrades.
The benefits of PoE will grow as more devices take advantage of the technology. Future revisions to the IEEE 802.3at standard should allow over 60 Watts for connected devices, so the range of applications will increase.
To download the full Particle Counters and PoE paper, click here.