Power over Ethernet (PoE) and Smart Buildings: Part 1

Power over Ethernet (PoE) is exactly what its name suggests: it delivers power over the same cable used for data transmission – enough for small devices. The technology is widely used in smart buildings, where normal power safety rules do not apply due to the lower voltages involved. This highlights one of the reasons PoE is attractive; it can greatly reduce costs related to installation and compliance.

By: Bob Card, US Marketing Manager, Advanced Solutions, ON semiconductor

Power over Ethernet (PoE) is exactly what its name suggests: it delivers power over the same cable used for data transmission – enough for small devices. The technology is widely used in smart buildings, where normal power safety rules do not apply due to the lower voltages involved. This highlights one of the reasons PoE is attractive; it can greatly reduce costs related to installation and compliance.

Since many office buildings already have Ethernet throughout the structure and an uninterruptible power supply (UPS) with battery backup installed, a robust system can be easily implemented. Additional PoE devices can utilize the same cables already deployed to power applications such as lighting and security cameras. Power can be delivered over the Ethernet cable to devices up to 100 meters away from PoE-enabled Ethernet devices.

The Benefits of Powering Smart Buildings with PoE

One obvious benefit of going with PoE is that it enables DC power to run over your existing Ethernet. While you’ll still need to update your network switches with PoE-capable ports, the cost-benefit of not having to run additional copper wiring for powered devices is enormous. The price of copper has risen from $0.65 a pound in 2000 to $4.05 a pound in 2021 (source: macrotrends). In addition, further cost savings can be achieved by not implementing AC-DC conversion on the powered device.

PoE is also more flexible for placing powered devices. Most AC power outlets are close to the ground, which is not an ideal location for Wi-FI® access points (APs), femto and pico cells, and cameras. To maximize coverage, it is recommended to avoid placing these devices near obstacles, preferably at ceiling height. Unlike the mains network, Ethernet cables often run through voids created by drop ceilings, removing another barrier to adoption.

PoE combines power and data to enable 24/7 intelligent monitoring of a variety of applications including lighting, security cameras and digital signage. A centralized PoE network equipped with a battery-powered uninterruptible power supply system (UPS) ensures continuous operation of critical equipment during outages.

Power over Ethernet (PoE) and Smart Buildings: Part 1
Figure 1: Benefits of PoE Smart Buildings

Smart Building Applications and PoE Standards

The PoE standard (IEEE 802.3af) was originally ratified in 2003 and provides up to 15 watts of power. It was widely used in applications such as IP telephony, building access control, and powered early distributed Wi-Fi access points. Later revisions of the standard, including IEEE 802.3at (30 watts/2009) and IEEE 802.3bt (90 watts/2018), increased the power provided to enable more demanding applications such as faster Wi-Fi Network, security cameras, audio speakers, point-of-sale (POS), LED lighting, etc.

Power over Ethernet (PoE) and Smart Buildings: Part 1
Figure 2: PoE Standards and Applications

PoE topology

Figure 3 shows a typical PoE topology. A PoE network switch is called a Power Sourcing Equipment (PSE) and it provides DC power to clients called Powered Devices (PD). The specification states that the PSE should be able to power the PD over an Ethernet cable (usually CAT5/6) of up to 100 meters.

Power over Ethernet (PoE) and Smart Buildings: Part 1
Figure 3: Typical PoE topology (Source: Ethernet Alliance)

Since Ethernet cables can go up to 100 meters, there is some dissipation over this distance, so in the worst case, the power reaching the PD is lower than that provided by the PSE. In the specs, 802.3af is 13 watts, 802.3at is 25.5 watts, and 802.3bt is 71.3 watts.For the “bt” standard, the DC voltage range of the PD is 42 to 57 volts[RB2]. Networked devices that do not support PoE at the input can still be connected and use a PoE splitter to separate data and DC power. This can also reduce the need for an AC-DC converter and place the device close to an AC outlet.

PoE powered PTZ camera

Today’s security systems typically use cameras that contain small motors that allow them to move in three axes, or pan, tilt, and zoom (PTZ), and typically employ high-definition digital cameras. These cameras can be manually controlled via a wired connection such as Ethernet, or programmed to automatically move and zoom when objects are detected within a defined window of interest or the entire field of view. Some cameras can also be configured to survey the scene with continuous 0° to 360° pan and 0° to 180° tilt, while zooming can be achieved using optical or digital techniques. The power required for these security and surveillance cameras can now be provided using PoE based on the IEEE 802.3at standard.

PoE powered wireless network

Wi-Fi access points and routers are also common applications of PoE. The power consumption of both is usually a function of supported speed and traffic. Modern networks use technologies such as MIMO (Multiple Input Multiple Output) to increase range and throughput. Implementing an AP/router application that supports Wi-Fi 6 (IEEE 802.11ax) speeds will map to the PoE standard as follows:

1. Wi-Fi 6, 4×4 dual-band concurrent: 802.3at
2. Wi-Fi 6, 8×8 dual-band concurrent: 802.3at/bt
3. Wi-Fi 6, 4×4 tri-band concurrent: 802.3at/bt

Although Wi-Fi routers/APs come with an AC-DC power supply in the box, they can also be powered using a PoE splitter. In contrast, products like the Cisco MerakiTM MR56 Wi-Fi 6 (802.11ax, 8 spatial stream) access point now support 802.3at, which means the RJ45 port can be connected directly to a PoE-capable PSE switch to power the device .

PoE powered picocells and femtocells

Picocells and femtocells are used to extend or increase cellular coverage, especially in busy areas such as buildings, offices, shopping malls and stadiums. Unlike regular cells, picocells typically have a small range, on the order of 200 meters or less, while femtocells may have a range as low as 10 meters. These tiny devices are ideal candidates for PoE, as shown in the following example:

1. ApexTM 4G/LTE 3.5GHz Outdoor Picocell (35 W): 802.3bt

PoE powered digital signage

LED TV is a very effective form of communication. They Display customized, dynamic digital signage in a variety of areas, including corporate office spaces, smart retail, hotels, and government municipalities. Like Wi-Fi, digital signage can only be beneficial if placed properly. For example, larger screens are often suspended from the ceiling so crowds can easily view content. In contrast, smart kiosk or point-of-sale (PoS) applications utilize smaller screens – some with touchscreens, for a more personalized and interactive user experience.

The power consumption of different LED TVs varies greatly. The Samsung® 55″ LED TV listed below specifies a typical power consumption of 69 W, while another LED TV of the same size and manufacturer requires 120 W. It is important to ensure that the power of the LED TV does not exceed the power of the PD. Use 802.bt standard, this can vary from 90 W to 71.3 W, depending on the length of the Ethernet cable between the PSE and the LED TV (PD).

There are also some signage TVs with PoE on the market. It will be interesting to see if LED TV makers start integrating 802.bt into their larger LED TVs to meet the demands of the growing digital signage market.

1. 55″, Samsung 4K LED TV (#Q70T) 69 W (typ): 802.3bt (requires PoE splitter
2. 46″, HD Thinlabs, Inc with touch screen: 802.3bt (no PoE splitter required)
3. 10″, Samsung Digital Signage (DB10E-TPOE) 802.3at (no PoE splitter required)
4. 48″, Samsung Digital Signage (DH48E) 44 W (typ) 802.3bt (requires PoE splitter)
5. 40″, Samsung Digital Signage (H40B) 44 W (typ) 802.3bt (requires PoE splitter)
6. 16″ medTV® PDI-P16TV-GB2-P TV (25 W) 802.3at (no PoE splitter required

PoE Zhilian Lighting

PoE and LED lighting are natural partners because LEDs consume DC power and PoE provides DC power. This allows you to eliminate AC-DC power conversion costs when powering your LEDs with PoE.

The ON Semiconductor Connected Lighting Platform (Figure 4) is a great example of how PoE can enhance smart buildings. Based on a modular design, the platform is capable of delivering 7,000 lumens to two strings of 16 LEDs, driven by dual FL7760 LED drivers. A PoE module based on the NCP1096 802.3bt controller provides up to 90 watts of DC power to the LED driver module. Meanwhile, there is a second connector on the LED driver module that accepts an RSL10 Bluetooth 5 radio for wireless connection to a smartphone gateway for cloud connectivity. This is smart lighting.

Power over Ethernet (PoE) and Smart Buildings: Part 1
Figure 4: Connected Lighting Platform with PoE Module

PoE powered business phone (VoIP)

Voice over Internet Protocol (VoIP) is probably the most common application of PoE. VoIP uses the Ethernet protocol to digitize low-frequency analog voice signals into data packets over a wide area network. From there, it will travel through switches and routers, into the cloud, and on its way to its destination. VoIP consumes only 4 to 7 watts, so it is very compatible with the 802.3af PoE standard. Modern VoIP phones with RJ45 connectors are designed to receive both data and power over an Ethernet cable, so an external PoE splitter is not required.


The convenience of providing power and data connectivity over the same cable is compelling; we’ll just have to see how USB has become a ubiquitous power source for many consumer devices. The same is true for PoE in commercial and industrial applications. It advances the concept of a single-cable solution, targeting applications that benefit directly from the simplicity it brings.

ON Semiconductor has mature expertise in digital communication and power management, and has the strength to provide good PoE solutions. As more manufacturers discover the benefits of PoE, end users will begin to demand PoE. Now is the time to start the transition to a smarter, integrated power/data combination.

Author: Yoyokuo