Powering smart buildings with Power over Ethernet - Embedded.com

Powering smart buildings with Power over Ethernet


The convenience of delivering power and data over the same cable is compelling, and just as USB has become a ubiquitous source of power for many consumer devices, Power over Ethernet brings multiple benefits to commercial and industrial applications.

Power over Ethernet (PoE) does exactly as the name suggests: it provides power – enough for small devices – over the same cable being used for data transfer. The technology is used extensively in smart buildings where, thanks to the lower voltages involved, normal mains electrical safety rules do not apply. This highlights one of the reasons why PoE is attractive; it can significantly reduce the costs associated with installation and compliance.

As many office buildings already have Ethernet flood-wired throughout the structure, with battery-backed uninterruptible power supplies (UPS) installed, robust systems can easily be implemented. Adding PoE equipment retrospectively can make use of the same cables already deployed, to also deliver power to applications such as lighting and security cameras. Power can be delivered over the Ethernet cable to devices that are up to 100 meters away from the PoE-enabled Ethernet equipment.

Benefits to Powering Smart Buildings with PoE

One of the clear benefits of adopting PoE is that it enables DC power to run across your existing Ethernet. While you do still need to update your network switches with PoE-enabled ports, the cost benefit associated with not having to run additional copper wiring to the powered device can be significant. The price of copper has risen from $0.65 per pound in 2000 to $4.05 per pound in 2021 (source: macrotrends). In addition, further cost savings can be made by not implementing AC to DC conversion at the powered device.

PoE also offers greater flexibility when locating powered devices. Most AC Mains electrical outlets are located close to the floor, which is not an ideal position for Wi-FI ® access points (APs), femtocells and picocells, and cameras. In order to maximize coverage it is advised to avoid locating these devices near obstructions, which means they are best placed at ceiling height. Unlike mains networks, Ethernet cables are often routed through the voids created by suspended ceilings, removing another barrier to adoption.

PoE’s marriage of power and data enables smart 24/7 monitoring and control of a variety of applications including lighting, security cameras and digital signage. Centralized PoE networks equipped with battery-powered Uninterruptable Power Systems (UPS) ensures continuous operation of critical equipment during power outages.

Figure 1: PoE Smart Building Benefits

Smart Building Applications and PoE Standards

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

Figure 2: PoE Standards and Applications

PoE Topology

Figure 3 illustrates a typical PoE topology. The PoE network switch is termed the Power Sourcing Equipment (PSE) and this provides DC power to clients, termed Powered Devices (PD). The specification stipulates a PSE should be able to deliver power to a PD across a maximum of 100 meters of Ethernet cable (typically CAT5/6).

Figure 3: Typical PoE Topology (Source: Ethernet Alliance)

As the Ethernet cable can reach up to 100 meters there is some dissipation over this distance, so under worst-case conditions the power reaching the PD is lower than that supplied by the PSE. This is covered in the specification as 13 Watts for 802.3af, 25.5 W for 802.3at and 71.3 W for 802.3bt. The DC voltage can range from 42 to 57 Volts [RB2]at the PD for the “bt” standard. Networked devices that do not support PoE at their input can still be connected and use a PoE splitter, in order to separate the data and DC power. This can also reduce the need for AC/DC converters and locating equipment close to an AC outlet.

PoE Powered PTZ Cameras

Today’s security systems generally use cameras that include small motors to enable them to move in three axes, or pan, tilt and zoom (PTZ), and typically feature HD digital cameras. These cameras can be manually controlled over a wired connection such as Ethernet, or programmed to automatically move and zoom when objects are detected in the defined window of interest or across the entire field of view. Some cameras may also be configured to survey a scene by constantly performing 0° to 360° pan and 0° to 180° tilt, while zoom can be implemented using either optical or digital techniques. The power needed for these security and surveillance cameras can now be delivered using PoE based on the IEEE 802.3at standard.

PoE Powered Wireless Networks

Wi-Fi access points and routers are also common applications for PoE. The power consumption for both is often a function of the speed and number of streams supported. Modern networks augment range and throughput using techniques such as MIMO (multiple input multiple output). Implementing an AP/router application that supports Wi-Fi 6 (IEEE 802.11ax) speeds would map to the PoE standards 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 boxed with an AC/DC power supply, they could also be powered using a PoE splitter. In contrast, products like the Cisco Meraki TM MR56 Wi-Fi 6 (802.11ax, 8 streams) access point now support 802.3at, meaning the RJ45 port can connect directly to a PoE-enabled PSE switch to power the device.

PoE Powered Picocells and Femtocells

Picocells and femtocells are used to extend or increase cellular coverage, particularly in busy areas such as inside buildings, offices, shopping malls and stadiums. Unlike a regular cell, the range of a picocell is typically small at around 200 meters or less, while the range of a femtocell could be as low as 10 meters. These tiny devices are ideal candidates for PoE, as one example below shows:

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

PoE Powered Digital Signage

LED TVs are a very effective form of communication. They can 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 is only as good as its location. For example, larger screens typically hang from the ceiling so crowds can easily view content. In contrast, smart kiosk or Point of Sale (PoS) applications take advantage of smaller screens- some with touch screens for a more personal, interactive user experience.

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

Several signage televisions with PoE are also available on the market. It will be interesting to see if the LED TV makers start integrating 802.bt into their larger LED TVs, for the growing Digital Signage market.

1. 55”, Samsung 4K LED TV (#Q70T) 69W (typ):                          802.3bt (PoE Splitter required)

2. 46”, HD w/ touchscreen by Thinlabs, Inc:                                    802.3bt (PoE Splitter not required)

3. 10”, Samsung Digital Signage (DB10E-TPOE)                         802.3at (PoE Splitter not required)

4. 48”, Samsung Digital Signage (DH48E) 44W (typ)                   802.3bt (PoE Splitter required)

5. 40”, Samsung Digital Signage (H40B) 44W (typ)                      802.3bt (PoE Splitter required)

6. 16” medTV ® PDI-P16TV-GB2-P television (25W)                     802.3at (PoE Splitter not required)

PoE Smart Connected Lighting

PoE and LED Lighting are a natural fit because LEDs consume DC power, and PoE delivers DC power. This allows you to eliminate the cost of AC-to-DC power conversion when powering LEDs with PoE.

A great example of how PoE enhances smart buildings is the ON Semiconductor ® Connected Lighting Platform (Figure 4). This platform is based on a modular design, able to provide 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 delivers 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 the RSL10 Bluetooth ® 5 radio for wireless connectivity to a smartphone gateway, enabling cloud connectivity. Now that is smart lighting.

Figure 4: Connected Lighting Platform with PoE Module

PoE Powered Business Phones (VoIP)

Voice over Internet Protocol (VoIP) is perhaps the most common application for PoE. VoIP digitizes low frequency analogue voice signals into packets of data using the Ethernet protocol over a wide area network. From there, it will pass through switches and routers and into the cloud, on to its destination. VoIP only consumes between 4 to 7 watts, so it is very compatible with the 802.3af PoE standard. Modern VoIP phones fitted with an RJ45 connector are designed to receive both data and power over the Ethernet cable, so no external PoE splitter is required.


The convenience of delivering power and data connectivity over the same cable is compelling; we only need to look at how USB has become a ubiquitous source of power for many consumer devices. The same is true for PoE in commercial and industrial applications. It advances the concept of single-cable solutions by targeting applications that can directly benefit from the simplicity it brings.

With established expertise in both digital communications and power management, ON Semiconductor is well placed to provide PoE solutions. As more manufacturers discover its benefits, end-users will begin to demand PoE. The time to begin the transition to a smarter, integrated power/data combination is here.

All trademarks are the property of their respective owners. ON Semiconductor is a trademark of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. Wi-Fi is a registered trademark of Wi-Fi Alliance®. Cisco Meraki is a trademark of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries. Apex is a trademark of Casa Systems, Inc. Samsung is a trademark of Samsung Electronics Co., Ltd. medTV is a registered trademark of PDi Communication Systems, Inc. The Bluetooth word mark and logos are registered trademarks owned by Bluetooth SIG, Inc.

>> This article was originally published on our sister site, Power Electronics News.

Bob Card is Americas Marketing Manager, Advanced Solutions Group at ON Semiconductor.

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