Tech Trailblazer: Class 4 Fault-Managed Power Systems for 5G and More

Raj Radjassamy, Director, 5G and wireless segment for ABB Power Conversion


The news that the National Fire Protection Association (NFPA) has defined a new class of power in the latest National Electrical Code edition (NEC 2023) has set the power engineering and architecture world abuzz with possibilities and use cases.

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Figure 1. Class 1, 2, 3, and 4 maximum voltage and power levels (NEC 2023 Edition)

­Power systems designers have, for decades, been limited by the strict guideposts on Classes 1, 2, and 3 circuitries, but the NEC’s newly defined Class 4 power (as laid out in Article 726) will offer a compelling alternative.

Fault-Managed Power Systems and How They Work

To understand the opportunities Class 4 power will present and the challenges it may face as it gains a foothold in the U.S., one must first understand how the technology works. Since the NEC began outlining guidelines for safe electrical circuitry, the principal strategy for enabling safe electrical installation has been limiting the circuits’ maximum power and/or voltage (see fig.1).

Classes 1, 2, and 3 all relied upon this approach to mitigate potential risk to people and property, with Class 2 emerging as the popular standard for commercial and residential deployments. However, limiting power and voltage can restrict technological advancements, particularly as engineers and inventors pursue high-powered designs. That’s where Class 4 power comes in. The newest addition to the NEC takes a different approach than its predecessors and may allow engineers and electricians to pursue applications that were previously out of reach.

Class 4 power utilizes fault-managed power systems (FMPS) to limit the current in fault conditions rather than limiting the overall power within a circuit. FMPS’ advanced sensing, monitoring, and control capabilities keep tabs on the circuit’s functions by checking for interruptions hundreds (or thousands) of times each second. Should the FMPS detect a fault, it’s designed to limit the energy within the circuit to a level that helps mitigate risks to people and/or property. The result is a safer, more reliable way to deliver large loads up to a maximum voltage of 450 V (figure 1).

Not only can FMPS technology check for generic interruptions, it also can identify the type of fault that’s taking place. These systems can differentiate between loads and human interference; respond to line-to-line and line-to-ground faults; identify series and parallel arcs; and recognize line-to-line and series-resistive faults. If a fault occurs, the FMPS cuts the power at the transmitter near-instantaneously. Once the fault condition clears, the transmitter can restart the power delivery (figure 2).

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Figure 2: Class 4 cables


Traditional wiring designs most often distribute AC power within conduits. Class 4 circuits may change that, as their design does not require any conduit provided they meet UL 1400-1 and Article 726 specifications. Replacing traditional AC power with higher-voltage (less than 450 V) Class 4 circuitry could improve efficiency, cost, and sustainability due to the lower current levels necessary for performance (and the subsequent reduced amount of copper required). It could also improve safety for technicians dealing with high-powered, high-voltage equipment.

Armed with this technology, engineers, inventors, and industrial designers are looking forward to the new innovations and applications that Class 4 power may enable. Data center operators, telecom service providers, and commercial builders will all benefit from the adoption of Class 4 as it may make applications like “smart” buildings, DC-powered data centers, and LED lighting with high power demands more feasible and cost-effective to deploy, maintain, and expand.

In the telecommunications industry, the potential benefits of Class 4 could be significant, especially as the 5G expansion continues. Rolling out a new-generation mobile network is always time-consuming and expensive, but the transition to 5G is proving more labor-intensive than previous shifts thanks to its unique power, coverage, and capacity demands. As such, providers are eagerly pursuing solutions that may ease the financial and logistical burdens of the undertaking.

Small cell radio deployments will be a primary driver of 5G expansion thanks to their relatively cost-effective builds and space-conscious designs when compared to macro towers. However, powering small cell equipment may be more complex than previous generation’s infrastructure due to the high power demands of 5G radios and the complicated web of deployment locations necessary to achieve comprehensive coverage. Class 4’s unique properties may offer a viable solution to this problem as it’s able to deliver large loads over longer distances than previous options and can do so without the need for conduits or certified technicians. Depending on installation location and coverage need, this combination could help meet small cell power needs in a cost-effective, innovative way.

These same properties make Class 4 power well-suited for deployments of indoor/outdoor distributed antenna systems (DAS), fixed wireless access (FWA) systems, and private networks, which can help provide high-speed access and throughput in large facilities including stadiums, parks, campuses, and hotels.

What’s standing in the way

Although this technology has the potential to usher in a new wave of innovation for the telecom industry, architecture, manufacturing, city planning, entertainment, and more, the change will not happen overnight.

To start, knowledge gaps and limited Class 4 FMPS availability may be barriers to adoption. Electricians, engineers, architects, and other decision-makers will need to learn about the best ways to deploy, work with, and maintain Class 4 power, and that will take time. At the same time, equipment manufacturers and designers will be working to develop the components needed to build high-voltage, fault-managed circuits and find ways to manufacture them reliably and at scale. Furthermore, possible wariness to work with such high-voltage circuitry could impact adoption until electricians and builders trust FMPS’s effectiveness for harm reduction.

Similarly, Class 4 power may not be an option for retrofits to Class 2 or traditional AC power due to the significant infrastructure changes that would be necessary to support the FMPS designs. It’s unlikely that network operators and building owners will undertake this kind of intense renovation and the associated expense unless the benefits for their use case or application outweigh the cost. Instead, Class 4 circuitry and its benefits will be more often seen in upcoming communications deployments and high-budget greenfield architecture (like stadiums, airports, public transit facilities, and data centers).

At present, the timeline for widespread adoption of Class 4 power remains unclear. It will partially depend on when regulators in each state in the U.S. make the necessary changes to adopt the 2023 version of NEC, which includes Article 726. As of December 2022, only 25 states were using the 2020 NEC. Those 25 might be expected to switch to the 2023 version sooner rather than later. That leaves 25 states that have yet to fully adopt the 2020 NEC and would likely lag behind in adopting the 2023 provisions. The timeline for global adoption is equally uncertain as regulatory bodies around the globe have yet to announce their intention to adopt FMPS-based circuitry into their guides.

One step (up or down) at a time

Opening this discussion and sharing knowledge about the ways to leverage this technology will be crucial as industries explore its potential and weigh the risks. Despite the fact that it has been in development for many years, its relative immaturity means the industry has much to learn. Power specialists and engineers have likely only scratched the surface of what’s possible.

Once it’s more widely available, great minds across industries will be able to experiment with and test the limits of these systems, which could open many doors for new deployments in the years to come. As the technology matures, more creative applications are likely to reveal themselves—and more challenges will arise.


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