A Closer Look at Class 4 Fault-Managed Power Systems in Smart Buildings
Authors: Authors: Gale Moericke (CRUX), Isaac Sachse (Belden), Miguelangel Ochoa (ITTERA)
Introduction
In our 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 4 fault-managed Power (FMP) systems.
FMP systems are a new way to deliver DC power that was adopted as Article 726 into the 2023 National Electric Code (NEC). These systems deliver significantly more power over longer distances compared to Class 2 systems like Power over Ethernet (PoE), but with the same or even higher level of fire safety and shock protection. FMP systems have the potential to revolutionize in-building power distribution in modern smart buildings.
What is Class 4 Fault Managed Power System?
Unlike Class 2 power-limited circuits that have a maximum output of 60 VDC and provide fire safety and shock protection by limiting power to 100 Watts (W), FMP systems provide fire safety and shock protection by limiting the amount of energy that can go into a fault. This unique capability is achieved with Class 4 transmitters and receivers that use built-in sophisticated circuit management and control software to actively monitor a circuit and immediately stop power in the event of a fault. Article 726 of the NEC defines these systems as follows:
“Class 4 fault-managed power systems consist of a Class 4 power transmitter and a Class 4 power receiver connected by a Class 4 cabling system. These systems are characterized by monitoring the circuit for faults and controlling the source current to ensure the energy delivered into any fault is limited.”
Per the NEC, Class 4 transmitters, receivers, cable, and connecting hardware that comprise a FMP system must be listed as such. Underwriters Laboratories (UL) 1400-1 specifies the requirements for Class 4 transmitters and receivers, including fault power and arc energy limits and grounding and isolation requirements. UL 1400-2 specifies the requirements for listed cables and connecting hardware, including output rating, conductor size, and insulation.
As shown in the diagram below of a Class 4 circuit, transmitter input power can be AC power from the utility grid, DC power from renewable energy sources like wind and solar, or power from DC microgrids that use alternative power sources (renewables, generators, etc.) in conjunction with battery energy storage systems. The transmitter converts incoming power to a format defined by the equipment manufacturer to energize the Class 4 circuit. At the other end of the circuit, a Class 4 receiver converts the power to whatever AC or DC format is required for the target load. Together, the transmitter and receiver continuously monitor the Class 4 circuit for faults and stop power within milliseconds upon detection.
It’s important to note that while UL 1400-1 defines fault and arc energy limits for Class 4 listed transmitters and receivers, it does not define specifically how a specific manufacturer’s equipment energizes or limits fault energy of a Class 4 circuit. This means that Class 4 circuitry components are proprietary and must be from the same manufacturer. A common method is to partition power into tiny digital energy packets that each check for fault conditions. Because the packets are so small, the amount of power delivered into a fault prevents any possibility of shock or fire ignition.
The Drivers Behind FMP Technology
Since the late 19th century, the power grid has used AC power to distribute electricity to cities and buildings due to its ability to deliver high voltages over long distances. It has also historically been used to distribute electricity throughout a building. However, AC power is inherently unsafe from a fire initiation and human shock perspective. Consequently, the NEC imposes several requirements on AC power circuits, from the insulation of the electrical cables themselves to the use of breaker panels, junction boxes, and metal conduit. AC power circuits also require installation by licensed electricians.
Over time, more endpoints have transitioned to using electronic components with intelligent semiconductors that operate via DC power, such as IT and audiovisual equipment, LED lighting, and variable speed motors, fans, and compressors used in a variety of building appliances and systems. To power these devices, AC power must be converted to DC power. This conversion results in power losses of up to 30%.[i] Experts estimate that over 70% of AC power today is converted to DC.[ii]
With the built environment accounting for 39% of annual global emissions, including 28% from the energy needed to power, heat, and cool a building, reducing power losses and effectively managing power consumption is essential in modern buildings.[iii] As the built environment becomes smarter and more technology-rich with equipment and devices operating via DC power, historical AC distribution power should be reexamined.
Class 2 power was introduced in the NEC more than thirty years ago as an alternative to traditional AC methods. Class 2 power is essentially the use of voltage and power-limited DC circuits, with up to 100W at the source. The power limitations of Class 2 circuits address the safety issues associated with traditional AC power and eliminate the need for AC power circuits in many situations, significantly reducing installation costs. However, Class 2 circuits impose other challenges.
Due to voltage drop over cabling distances, the maximum Class 2 power received at a load is typically 75 to 90W. Many devices require more power than a Class 2 circuit can deliver. Furthermore, Class 2 circuits are distance limited. Power over Ethernet (PoE), a popular type of Class 2 power that allows for the concurrent transmission power and data over twisted-pair copper cabling, is limited to about 71W of power received at a load and a distance of about 100 meters. While non-PoE Class 2 power can extend beyond 100 meters, it is also distance limited due to voltage drop. Even with larger 12 AWG copper conductors, non-PoE Class 2 circuits can typically only deliver 75W of power to about 457 meters.[iv] (See the companion blog post on Class 2 power for more information.)
FMP systems were introduced as a means to deliver more power over longer distances while maintaining the same or even higher level of safety as Class 2. Like PoE before it, FMP technology is disrupting the market. The first patents for the technology were issued in 2014 and initial transmitters and receivers hit the market soon after. With several compelling use cases, FMP systems were able to gain market traction. However, because the technology did not fit into any existing NEC definitions for power circuits, many code officials were reluctant to permit FMP systems. To codify these systems, Class 4 circuits were ultimately added to the 2023 edition of the NEC as an entirely new Article 726. In conjunction, UL developed UL 1400-1 and 1400-2 requirements for listing equipment and cabling. FMP systems from various manufacturers are now available in the marketplace, and several companies formed the FMP Alliance to promote the technology and encourage adoption.
Advantages of FMP Systems
FMP systems offer the following advantages:
- Safe delivery of higher power over longer distances: A FMP system is an inherently safe option for delivering higher power over longer distances compared to Class 2 systems, which are also inherently safe. Distances vary based on manufacturer transmitter and receiver, as well as conductor sizes and numbers of conductor pairs. For example, some available FMP systems can deliver 470W to 500 meters and 205W to 1500 meters over a single 18 AWG pair, while others can deliver 600W or even 1,000W to more than 1000 meters using two or four 18 AWG pairs.
- Reduced deployment costs: Similar to Class 2 systems, FMP systems eliminate the need for separate AC power circuits and associated breaker panels, conduits and other mechanical protection that require installation by licensed electricians in many jurisdictions, reducing material and deployment costs.
- Improved efficiency: The power and distances enabled via a FMP system make it an ideal as a whole-building power distribution infrastructure, replacing the bulk of conventional AC power circuits in a building. FMP systems can therefore significantly reduce AC to DC power conversion and associated energy loss, significantly improving power efficiency and reducing operating costs. FMP systems also have centralized management capabilities for actively monitoring and controlling electricity usage to further improve efficiency.
- Convergence: Like non-PoE Class 2 systems, FMP systems can be deployed using hybrid copper-fiber cables that converge both power and data into a single cable, requiring only a single cable pull and delivering power and data to devices over much further distances for easier installation and labor, space, and material savings. This is especially ideal for greenfield projects.
- Sustainability: In addition to reduced material and improved efficiency, Class 4 transmitters can accept native DC power from renewable sources (solar, wind, DC microgrids, battery storage, etc.). This can help drive the adoption of DC microgrids and reduce reliance on conventional carbon-emitting energy sources in support of net-zero objectives.
FMP systems are especially advantageous for smart buildings. With the ability to operate at up to 450 V (including AC or DC power) with no specified limit on the amount of power delivered and extended distances, the technology is extremely flexible. Product designers can essentially design the output of the Class 4 receiver to deliver whatever power is needed for varying distances, offering opportunities to power an ever-growing range of equipment and devices.
FMP systems have the potential to drive PoE and smart building device adoption because they can be used to power PoE switches, injectors, optical network terminals, and other equipment that connect and power smart building devices.
The centralized software management functionality of FMP systems also supports more sophisticated energy monitoring and control in support of smart building goals. This capability allows facility operators to determine and control how power is consumed at a very granular level and can:
- Eliminate the need for sub-metering in a multi-tenant space
- Assist with demand response or other energy management programs
- Identify energy wasted on unoccupied areas of a facility
- Detect devices consuming energy outside of normal consumption bands
- Cycle power off and on to devices remotely instead of dispatching technicians
Applications and Use Cases
FMP systems are already established as a viable commercial solution. Early successful deployments include stadiums and outdoor venues where cable distances are very long.[v] In these environments, FMP systems have proven to be an excellent solution for powering wireless antennas (e.g., 5G small cells, distributed antenna systems, Wi-Fi access points), security systems, and other technologies spread throughout large facilities and grounds. Large warehouses, distribution centers, and industrial facilities have similar challenges.
Smart high-rise office and hotel buildings have also used FMP systems to distribute power from a central location vertically to all floors. In this scenario, FMP systems can power PoE switches that that then deliver power and connectivity horizontally for various in-room smart technologies, such as lighting, shades, entertainment, and digital climate controls. Because Class 4 transmitters can accept DC power directly from renewable energy sources and on-site battery storage without AC-to-DC and DC-to-AC conversion losses, it is especially ideal for commercial facilities striving to improve efficiency and achieve net-zero status. The Hotel Marcel in New Haven, Connecticut deployed a FMP system alongside a DC microgrid to become the first net-zero hotel in the U.S.[vi]
FMP systems are an excellent method for powering high-capacity LED lights that require more power than can be provided by Class 2 systems, such as those used in controlled indoor agriculture facilities.[vii] It is also ideal for distributing power for intelligent PoE lighting systems. In this scenario, hybrid-copper cables employ Class 4 cables for power and fiber for data to distribute power and connectivity to remote PoE switches distributed throughout a facility. PoE switches and power supplies can then power smart LED lighting via lighting controllers (nodes).[viii]
Other potential use cases include powering network and audiovisual equipment, USB hubs, digital displays (e.g., video walls and billboards), remote kiosks, electric vehicle (EV) charging stations, optical network terminals, building automation controllers, elevators, Class 3 public address systems, and more. Large data center operators are even now evaluating FMP systems as a means to deliver direct DC power to servers, which will significantly improve power efficiency in data center environments and support the use of sustainable DC microgrids for these power-hungry facilities.[ix] The graphic below shows an example of a commercial building using FMP systems for in-building power distribution in conjunction with an onsite DC microgrid and a variety of Class 2 power circuits (e.g., PoE, SPoE) and even Class 3 circuits commonly used in public address and nurse call systems.
More to Come
FMP systems are essentially an intriguing alternative to traditional methods of power distribution for any large footprint facility needing to deliver higher power over longer distances. It is not an incremental improvement to existing power delivery methods, but rather a major paradigm shift. Future innovations and applications are likely to follow as the FMP marketplace evolves and matures. Some manufacturers are also looking to integrate Class 4 receivers and other load side functionality into individual devices, which will further expand the types of equipment and devices that can be powered with this technology.
Smart building owners, architects, and system designers would be wise to learn about innovative Class 4 FMP systems as an inherently cheaper, safer, smarter, and more efficient option for in-building power distribution.
References
[i] Cisco: Replacing AC with DC and PoE for Everything, Rob Enderle, 2022
[ii] DC: The power to change buildings, Brian T. Patterson
[iii] Bringing Embodied Carbon Upfront, World Green Building Council
[iv] Overview: Corning Remote Power Solution, Composite Cable Distance Lengths, Corning
[v] Case Study: Circa Resort & Casino Las Vegas, Belden
[vi] Hotel Marcel: Where historic architecture meets smart, net-zero technology, Buildings Magazine
[vii] Constellation’s Technology Ventures group Invests in Fault Managed Power and the Future of Controlled Environment Agriculture (CEA), Indoor Agtech
[viii] Mouser Electronics Fuses Efficiency and Sustainability with PoE lighting Architecture, Buildings Magazine
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.
