PoE was originally used in a proprietary Voice over IP (VoIP) system developed by Cisco in 2000. Each new generation of PoE standards and technologies includes higher power specifications. At the same time, the efficacy of LED lamps is also increasing year by year. By 2017, the 25.5W limit stipulated by the IEEE 802.3at standard, which has now been replaced, is enough to power nearly a quarter of the lamps in the room.
The IEEE Standards Council approved the IEEE 802.3bt standard on September 27, 2018, including some important improvements to LED lighting systems. The main driver of this improvement is the use of four pairs of network cables to transmit up to 90W of power over 100m of cable. This allows multiple fixtures to be daisy-chained, simplifying the installation process.
Other enhancements in the new specification include increasing the efficiency of current PoE levels (that is, 25.5W output power), as the power consumption of the cable is reduced by approximately half. For example, a power supply device operating under the previous standard needs to provide at least 30W of power to ensure that the powered device receives 25.5W of power, as Ethernet cables may lose up to 4.5W of power. Powering the same device under the new standard will reduce losses to below 2.25W and increase efficiency by about 7%.
In addition, power supply equipment can now determine the maximum power consumed by each connected device and set the output power accordingly, thereby improving the operating efficiency of the entire system. Finally, as the duty cycle required to maintain the power signature is reduced, the standby power requirement is now reduced, and the only 0.02W is required to maintain the power connection. Since energy efficiency is likely to be the most compelling selling point of LED lighting systems, changes to the new specification will help advance the development of PoE control systems.
The author recently visited Carthage, Missouri for a visit to H. E. Williams. The details of the PoE system are very instructive. As shown in Figure 1, a PoE lighting system includes five basic components: a network controller, a user interface, a PoE switch, lamps, and auxiliary equipment such as sensors or switches.
The data and power receiving of the luminaire is achieved by adding a “node” in the luminaire housing and connecting it to the power and dimming input of the LED light engine. Depending on the function of the connected luminaire and its associated auxiliary equipment, this node can also handle other functions. Igor’s nodes allow multiple devices to connect to a PoE network.
According to the new IEEE 802.3bt standard, Igor has made some modifications to its node shape to make it closer to the size of traditional LED drivers. Another great enhancement is the addition of a USB port, as shown in the bottom left corner of Figure 3.
As the number of AC-DC power conversions is reduced, PoE lighting systems can provide higher overall energy efficiency compared to traditional AC power systems. Ethernet cable loss appears to be a major consideration in assessing total system power consumption, and this indicator is especially important for end users who want to gain subsidies by improving energy efficiency.
“NEMA / ANSI C137.3-2017 Minimum Requirements for Installation of Energy Efficient Power over Ethernet (PoE) Lighting Systems” document provided Installation requirements. Specifically, the standard specifies a minimum wire gauge, which requires the average resistance wire loss to be less than 5% of the total transmission power (assuming an average cable length of 50 meters). However, because each installation is more or less different, the total loss must be evaluated on a case-by-case basis. There are no guiding standards for assessment methods.