A Closer Look at Class 2 Power in Smart Buildings
Authors: Gale Moericke (CRUX), Isaac Sachse (Belden), Miguelangel Ochoa (ITTERA), Sekhar Kondepudi (Cisco)
Introduction
In our last blog, “Enabling Smart Buildings Through Evolution in DC Power,” we looked at how innovative direct current (DC) power technologies are revolutionizing in-building power distribution. This blog delves more into Class 2 power-limited circuits like Power over Ethernet (PoE).
PoE is a special type of Class 2 power based on IEEE 802.3 standards that allow for the concurrent transmission of low-voltage DC power and data from power sourcing equipment (PSE) to powered devices (PDs) over twisted-pair copper Ethernet cable, like Category 6 or 6A. It enables powering a variety of connected devices over the same category cables used to transfer Ethernet data, eliminating the need for separate alternative current (AC) power circuits. This integration of both DC power and communications is especially relevant for the Building Internet of Things (BIoT), making PoE technology essential for smart buildings and their interconnected devices.
Advantages of PoE
PoE is a highly cost-effective, reliable, and adaptable method for powering connected devices in a local area network (LAN). It offers significant cost reductions and new benefits for smart work and living spaces. PoE provides the following key benefits:
- Reduced Cabling and Installation: By eliminating the need for separate AC power circuits and associated conduits that require installation via a licensed electrician, PoE significantly reduces material and labor costs while streamlining installation.
- Efficiency: PoE facilitates centralized power control and monitoring for enhanced insight, control, interconnectivity, and automation that improves operational efficiency, reduces maintenance, and delivers superior energy savings.
- Flexibility: Without the need for electrical outlets, devices like monitors, security cameras, and wireless access points (WAPs) can be optimally placed and easily moved as needed. Building operators have greater flexibility in workplace design because they can design spaces based on user needs rather than outlet locations.
- Safety: Class 2 power is considered a limited-power application, meaning it is considered safe from fire initiation and provides acceptable protection from electric shock. PoE technology is also designed to intelligently protect network equipment from overload, insufficient power supply, and incorrect installation, eliminating risks associated with high-voltage power sources.
- Reliability: PoE sources its power from a centralized, universally compatible source—typically PoE-enabled network switches—instead of distributed wall adapters. PoE power sources can be backed by an uninterruptible power supply (UPS), ensuring continuous operation even during power outages. Powered devices can be easily disabled or reset from a central controller.
- Scalability: The ability to power devices on the same network used for data communications facilitates new device installation and network management, allowing building operators to take advantage of emerging smart building technologies.
IEEE Standards for PoE
The Institute of Electrical and Electronics Engineers (IEEE) defines Ethernet protocols in the IEEE 802.3 series of standards. Among these, IEEE 802.3af, 802.3at, and 802.3bt standards outline physical layer and management parameters for PoE over four-pair copper Ethernet cables. These standards have evolved over the past twenty years to deliver higher power levels. With the introduction of single-pair Ethernet (SPE) for lower-speed building automation system devices, the IEEE also introduced standards for delivering PoE over a single pair (SPoE).
Current IEEE PoE standards include:
- IEEE 802.3af-2003 (PoE or Type 1): Operates at 44 to 57 VDC to deliver up to 15.4 W over 2 pairs, supplying up to 12.95 W to devices operating at 37 to 57 VDC
- IEEE 802.3at-2009 (PoE+ or Type 2): Operates at 50 to 57 VDC to deliver up to 30 W over 2 pairs, supplying up to 25.5 W to devices operating at 42 to 57 VDC
- IEEE 802.3bt-2018 (PoE++ or Type 3 and Type 4): Operates at 50 to 57 VDC to deliver up to 60 W (Type 3) over 4 pairs, supplying up to 51 W to devices operating at 42 to 57 VDC, or up to 90 W (Type 4) over 4 pairs, supplying up to 73.2 W to devices operating at 42 to 57 VDC
- IEEE 802.3cg-2019 (SPoE): Operates at 24VDC or 55 VDC to deliver up to 8.4 W or 52 W respectively over one pair to low-speed SPE devices, such as building automation system sensors and controllers. The amount of power available for devices depends on output voltage, gauge size, and cable length.
Because PoE-enabled devices have a broad range of power requirements, IEEE 802.3 PoE standards categorize the four types of PoE into eight different classes, as shown in the table below. Per IEEE standards, PoE power is supplied only after device detection and classification via low-voltage pulses. Higher PSE types use multiple pulses to identify device class 1 through 8. Type 2 and above devices support Link Layer Discovery Protocol (LLDP) to communicate precise power requirements for greater efficiency.
Extending PoE Distance
Copper Ethernet cabling has evolved in tandem with PoE, enabling unique applications that adhere to the IEEE 802.3 standards. One such advancement is extended PoE over 4-pair cabling beyond the traditional 100-meter limit. While distances beyond 100 meters do not comply with industry cabling standards, extended distances are possible via twisted-pair cables engineered with headroom beyond industry standards and/or cables that use larger copper conductors such as 22 AWG. Larger conductors have less resistance and can carry more power over longer distances.
Similarly, SPE, which has emerged as a significant development in the smart building sector, can deliver power beyond 100 meters. Per the IEEE 802.cg standard, SPE allows for 10 Mbps data rates over a single pair of conductors up to 1000 meters. The standard also includes SPoE, which can deliver up to 52W, depending on the output voltage, gauge size, and cable length. For example, studies show that 18AWG SPE cable can deliver 7.7W of SPoE power to 1000 meters and 20W to about 445 meters, while 23AWG SPE cable can reach 400 and 145 meters, respectively.
These innovations are particularly valuable in the growing Internet of Things (IoT) space, where an increasing number of remote low-power, low-data devices such as sensors require power at distances greater than 100 meters. Both extended-distance PoE and SPE are useful tools for powering these devices in modern smart buildings.
Non-PoE Class 2 Power
Another means of extending power beyond 100 meters is to use non-PoE Class 2 power over simple copper conductor pairs. Per the National Electric Code® (NEC®), Class 2 circuits are limited to 100 W per circuit, which can be fully utilized with non-PoE systems that do not rely on IEEE PoE protocols and twisted-pair Ethernet cabling. Non-PoE Class 2 power uses centralized listed power supply units (PSUs) that convert grid AC power into Class 2 compliant DC power for delivery to devices. PSUs are typically mounted in a network equipment rack. Conductors carrying the non-PoE Class 2 power from the PSU to the device usually range from 16 to 20 AWG, depending on the device’s power requirements and distance. Non-PoE Class 2 systems can also be daisy chained to support multiple devices.
Non-PoE Class 2 power works well for devices that do not need a data connection. It also works well for devices that connect to the network via fiber optic cabling, enabling greater distances than PoE over copper Ethernet cables. Several manufacturers offer hybrid copper-fiber cables with copper conductor pairs for power and fiber for data bundled together within the same sheath, allowing a single pull to devices. Distance capabilities vary based on the size of the conductors. For example, a hybrid fiber-copper cable with a 16 AWG copper conductor pair can deliver 75 W up to about 182 meters, while a hybrid fiber-copper cable with a 12 AWG copper conductor pair can deliver 75 W up to about 457 meters.[i]
Applications and Use Cases
The evolution of PoE greatly expands the range and types of smart building devices that can be powered and connected via copper Ethernet cabling, driving increased adoption and more PoE-enabled devices introduced into the market. While initially used to power clocks, VoIP phones, WAPs, routers, surveillance cameras, and access control devices, PoE is now powering computer monitors, digital LCDs, and TVs to LED lights, window shades, laptops, thin client devices, HVAC sensors and controllers, and other smart building devices. The table below provides an overview of devices and applications for the specific type of PoE.
* For SPoE, maximum power available at the device depends on output voltage, gauge size, and link length
The following are some of the unique use cases for PoE and Non-PoE Class 2 power.
Smart Sit-Stand Desks
Smart sit-stand desks leverage PoE to power the vertical up and down movement, as well as peripherals such as phones, lighting, laptops, and monitors. PoE can also be used in this application to power USB hubs for charging personal devices (e.g., phones, speakers, headphones, etc.)
Personalized Airflow
In commercial buildings using centralized air duct systems, PoE can be used to power personalized air vents that improve individual comfort and optimize HVAC systems for energy savings as illustrated below.
SPoE-Powered Cameras
In smart buildings, one growing application for SPoE technology is surveillance cameras. Due to advanced compression techniques, typical security cameras only require 10 Mbps speeds and can be powered with less than 20 W, with some operating at less than 10 W. When implemented via IEEE 802.3cg SPE standards (10BASE-T1L) with the appropriate gauge cable, remote cameras can be connected and powered up to 1000 meters away. However, one caveat is that not all cameras are designed to natively support SPE and instead rely on standard RJ45 connectors. Fortunately, SPE-to-RJ45 remote adapters are available that convert SPE and SPoE to traditional 4-pair Ethernet (BASE-T) and POE for a functional link.
PoE Lighting
PoE lighting reduces installation costs by eliminating separate AC power wiring and improves energy efficiency by minimizing power conversion losses. PoE lighting enhances smart buildings via centralized lighting control and management that optimizes lighting quality and energy usage via scheduling, color tuning, dimming, and other capabilities. PoE lighting systems can also integrate with a variety of smart building sensors (e.g., occupancy, daylight harvesting, temperature, air quality, etc.) and communicate with other building systems (e.g., HVAC, security, etc.) for streamlined automation and building management. For example, PoE lighting sensors can detect occupancy and trigger an HVAC system to adjust temperature and airflow accordingly.
PoE lighting fixtures typically leverage external or integrated PoE nodes or gateways that serve as the IEEE-compliant interface. PoE nodes/gateway also act as the controller interface and can integrate additional input/outputs for sensors and wall switches. Depending on the power requirements of the fixtures, PoE nodes/gateway can be used to power multiple LED fixtures in a daisy-chain configuration.
Passive Optical LANs
One common use case for non-PoE Class 2 Power is a passive optical LAN where power is delivered over copper conductor pairs (either separately or as part of a hybrid copper-fiber cable) to optical network terminals (ONTs). These ONTs in turn provide PoE and connectivity to devices over twisted-pair copper category cables.
A Bright Future
The future is bright for Class 2 PoE. Its cost, efficiency, and safety benefits, combined with an ever-increasing demand for connected devices, will continue to drive market growth and the development of more PoE end devices. According to market research forecasts, the PoE market valued at over $1.4 billion in 2023 is expected to grow at a rate of 22.8% and reach nearly $9 billion by 2032.[ii]
For some applications, the distance and power limitations of Class 2 power may drive a shift to newer Class 4 fault-managed power (FMP) systems that can deliver more power over longer distances with the same or higher level of safety as Class 2. (See the companion blog post on Class 4 power for more information.) However, FMP systems are still an emerging technology and not considered a replacement for PoE. In fact, most industry experts see FMP systems as a complement to PoE and critical driver for increased PoE adoption. A key application for FMP systems will be the delivery of safe, efficient power to switches, injectors, and optical network terminals that deliver PoE and provide connectivity for smart building devices, enabling an all-DC power distribution infrastructure for modern buildings.
[i] Overview: Corning Remote Power Solution, Composite Cable Distance Lengths, Corning
[ii] Global Power Over Ethernet Market Overview, Market Research Future
This blog was developed by members of the TIA Smart Building Program Workgroup. This workgroup includes participants from all aspects of the smart building ecosystem to bring objective, holistic, and technology-neutral criteria for the industry to leverage in verifying the performance of smart buildings.
To participate in TIA’s Smart Building Program, contact membership@tiaonline.org
The ideas and views expressed in this guest blog article are those of the authors’ and not necessarily those of TIA or its members companies.
