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The Promise of DC Power Distribution

April 1, 2024
What electrical professionals need to know about this emerging trend on the path to decarbonization and net-zero energy.

The Biden Administration’s Executive Order 14057 establishes an ambitious plan to make all federal facilities net zero by 2045. New York City Local Law 97 establishes strict emission limits for buildings over 25,000 square feet, requiring a 40% reduction in emissions by 2030 and an 80% reduction by 2050. California, Maryland, Massachusetts, Michigan, Nevada, North Carolina, Virginia, Washington, and other jurisdictions also have state executive orders and statutes requiring net-zero or near-net-zero buildings by 2050, with several requiring significant carbon emissions reduction by 2030.

In addition, corporate environmental, social, and governance (ESG) initiatives are driving real estate owners and operators to implement ambitious net-zero targets. In 2020, the New Building Institute (NBI) verified 700 net-zero facilities in North America, and they say that number is increasing by as much as 50% every two years. Commercial facilities are also seeking to leverage the benefits of programs such as the U.S. Green Building Council’s (USGBC) LEED Zero Energy and LEED Zero Carbon programs and tax incentives like those available through the 2022 Inflation Reduction Act (IRA).

As more commercial buildings strive to decarbonize, electrical professionals could increasingly become involved with direct current (DC) power distribution projects. Thankfully, technology, codes, and best practices are evolving to facilitate this new way of powering the built environment.

Why is DC power distribution gaining attention?

Building electrical infrastructure has long used alternating current (AC) due to its compatibility with the grid, ability to deliver higher voltages over long distances, and easy transformation to support various loads. However, in today’s commercial buildings, all electronic equipment and devices internally operate using DC power. LED lighting, electrical vehicle (EV) chargers, variable speed drives for HVAC equipment, as well as some fans and blowers use DC power.

Electrical professionals are well-versed in delivering traditional AC power to DC-powered building loads via transformers, LED drivers, power supplies, and other conversion technologies. Conversion also occurs internally for many electronic devices or externally using “wall wart” adapters that plug into AC power outlets. Each time this conversion happens, it introduces energy losses, sometimes up to 30%.

Onsite DC microgrids are emerging for commercial buildings to decarbonize and meet net-zero and ESG initiatives. A DC microgrid consists of a renewable energy source like solar photovoltaic (PV) systems and small-scale wind turbines, as well as fuel cells and battery energy storage systems (ESS) — all of which produce native DC power. Converting DC power from a microgrid to AC power for distribution throughout a building, only to be converted back to DC, is highly inefficient. An all-DC power distribution system can eliminate the bulk of AC-to-DC conversion and provide the opportunity to deliver power from DC microgrids directly.

A DC microgrid with DC power distribution qualifies for sizeable tax credits under the 2022 IRA — even to the point where total investment can compete with traditional AC building power. It also provides cost savings and resiliency for building owners and operators by offering independence from the electric utility grid, storing energy gathered during peak renewable generation for use during non-peak hours, and enabling building operation during power outage events. While a DC microgrid allows buildings to disconnect from the electric utility grid, it is best practice to remain connected to the grid with net metering to ensure backup power if renewable energy sources stop generating electricity and feeding any excess energy generated back into the grid for additional savings or revenue, as well as overall improved grid efficiency.

What are the options for distributing DC power?

When it comes to powering building loads with DC power, there are multiple options available per the latest edition of the National Electrical Code (NEC), including:

  • Class 1 circuits – Limited to 600V, Class 1 DC circuits are deployed for larger power loads, including 380VDC used to power networking equipment in data centers, HVAC systems, electric vehicle (EV) chargers, and other large loads.
  • Class 2 circuits – Class 2 circuits are limited to less than 60V and 100W and are considered safe from a fire and electric shock perspective. Familiar Class 2 deployments in commercial buildings include 24VDC or 12VDC power distribution over multi-circuit (MC) cables for LED lighting, alarm panels, legacy CATV surveillance, relays, and more. Power over Ethernet (PoE) is a type of Class 2 power transmitted from power sourcing equipment (PSE), such as a network switch, over twisted-pair Ethernet cabling (e.g., Category 6A, 6, 5e). PoE is delivered simultaneously with data and control information to networked IP-based devices (PDs) such as wireless access points, surveillance cameras, access control panels, and IoT devices. PoE is also increasingly used for powering and controlling LED lighting via direct connections to luminaires or intelligent nodes that manage power and control for multiple fixtures. The types and classes of PoE are defined by IEEE 802.3 Ethernet standards as shown below. PoE lighting systems typically require the higher power levels offered by Type 3 or Type 4 PoE (Table).
  • Class 4 circuits – Class 4 power was recently adopted in Art. 726 of the 2023 NEC with a voltage limit of 450V. Class 4 power is considered fault-managed power (FMP), a technology pioneered as Digital Electricity (DE) by VoltServer. FMP systems safely transmit bulk DC power over 24 to 6 AWG conductors using centrally managed transmitters and remote receivers to intelligently detect faults and immediately stop transmission, providing the same level of protection from electric shock and fire initiation as Class 2 circuits. FMP cables, transmitters, and receivers must be listed per the NEC. UL 1400-1 specifies the requirements for transmitters and receivers, and UL 1400-2 specifies the requirements for cables and connecting hardware. (Note that the requirements for Class 4 cables are covered under a new Art. 722 in the 2023 NEC). The power and distance capabilities of an FMP system vary based on specific vendors’ technology and the number and size of conductors. For example, VoltServer’s DE system operates at 336VDC, delivering 300W and 600W to approximately 1,200 ft over one and two 18 AWG conductor pairs, respectively. It can reach levels up to 2,000W using multiple pairs of larger conductors.
  • Universal serial bus (USB) – Traditionally used for computer peripherals, the latest USB technology can deliver data and up to 240W of DC power to shorter distances of about 3.3 ft via much smaller connectors. USB can power many devices, including smartphones, tablets, laptops, video displays, and other personal devices. USB power is typically delivered via computers or other power and data rendering devices (e.g., network switches) or USB receptacles per Art. 406 of the 2023 NEC.  

As a new, safe, and cost-effective way to deliver bulk DC power, Class 4 FMP systems are increasingly gaining attention for DC power distribution in commercial buildings. FMP systems have the potential to connect directly to onsite DC microgrids and deliver DC power to equipment and devices throughout a building. Equipment and devices that can accept Class 4 FMP are being developed, including network switches, LED lighting drivers, HVAC controllers, EV chargers, and more. Multiple PoE network switches are now available that can be powered directly via Class 4 FMP. These switches then deliver Class 2 PoE or USB DC power to a wide range of connected devices throughout a building. As shown below, a DC microgrid with FMP, PoE, and USB technologies enables an all-DC power distribution system (Figure).

How does DC power distribution impact your business?

DC microgrids with a DC power distribution system using Class 4 FMP, PoE, and USB can provide cost savings and opportunities for electrical professionals, but there are considerations.

Class 4 FMP cables are smaller and lightweight compared to equivalent AC power cables used in traditional branch feeder circuits. Ethernet cables for Class 2 PoE circuits are also smaller than Class 2 MC cables, comprising about 80% less copper material. The smaller footprint of FMP and PoE cables saves significant space, especially in historical reuse projects. Class 4 and Class 2 PoE cables can reside in the same enclosure, raceway, or cable routing assembly, with no conduit required in most environments. Eliminating the time and material necessary for deploying conduits provides the opportunity for electricians to achieve higher project margins. Class 4 FMP and PoE systems further reduce cost by eliminating the need for AC circuit panels and installation via master electricians. Additional benefits of a DC power distribution system are centralized management for control and metering and the ability to intelligently share power across various loads, potentially lowering the amount of incoming building power required.

Not every project, however, can benefit from DC power distribution. For smaller projects, especially those that don’t have an onsite DC microgrid, a complete DC power distribution system with Class 4 FMP replacing traditional AC power feeders and branch circuits does not typically provide significant financial and efficiency benefits. In this case, sticking with conventional AC power distribution to primary building loads may make more sense. However, deploying PoE for lighting almost always delivers savings and efficiency due to improved reliability with centralized monitoring, control, and backup power. PoE lighting also enables integrating connected sensors, transforming lighting into a smart platform that can collect and act on information about the environment — everything from temperature and ambient light levels to air quality and occupancy.

Another primary consideration is the adoption of local codes. According to the National Fire Protection Association, as of March 1, 2024, only eight states have adopted the 2023 NEC — Wyoming, Colorado, Minnesota, Massachusetts, Oregon, Idaho, Ohio, and Texas. Most states still recognize the 2020 or 2017 versions of the Code. Local ordinances and the requirements of AHJs also vary. This can create significant barriers to deploying Class 4 FMP systems that AHJs may not recognize. Additionally, some locales may not allow the use of Class 2 PoE circuits for UL 924 egress lighting; if they do, cables often must be placed in conduit for protection.

Electricians have the advantage of understanding luminaire placement and installation for PoE lighting systems. However, because these systems reside on the network, careful coordination with IT professionals ensures the most cost-effective investment, adequate pathway space, and infrastructure and equipment support. For example, PoE lighting systems only transmit tiny amounts of control information. They typically do not require the same expensive networking switches that IT professionals use for connecting and powering network devices, such as wireless access points.

How can you ensure success as adoption accelerates?

While all-DC power distribution throughout a building is still in its infancy, the recent addition of Class 4 FMP in the NEC and the growing adoption of DC microgrids and PoE lighting will increase adoption over the next three to five years. According to Markets and Markets, the global microgrid market is projected to more than double in value by 2028 at a rate of more than 20%. Several DC microgrid projects are underway across the country — from a Maryland smart energy bus depot and a California major food producer to a Washington, DC university and several military bases. Electrical professionals will increasingly encounter projects that specify a DC microgrid and DC power distribution.

The key to success for electrical professionals is to expand their knowledge about emerging DC power technologies like FMP and PoE and engage early and often through design and construction phases to understand requirements and ensure careful coordination with other trades. It is highly recommended for electrical professionals to partner with industry experts who have comprehensive experience in DC power infrastructure and technology. These experts can provide infrastructure design assistance, equipment and component selection criteria, and project management to ensure robust DC power distribution systems that are cost-effective and efficient.

About the Author

Luis Suau

Luis Suau is the chief business officer at Sinclair Digital. With more than 40 years of industry experience in digital building solutions, he oversees business and product development for a full-service consulting, design/build, and project management firm specializing in sustainable and intelligent buildings with a primary focus on DC power and microgrids, building controls, and battery energy storage systems, including acting as a value-added reseller (VAR) of products, packaged systems, and software services. For more information, visit www.sinclair-digital.com.

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