The future may be a long way off. Households with entire Class 4 wiring seem like a dream. Excitingly, the new NEC issue may have taken America’s first step in that direction!
by Kevin Smith
The next edition of the National Electrical Code (NEC) will introduce a wiring method that has the potential to fundamentally change electrical installations, upend electrical safety, revive DC distribution, and reduce emissions. Quite a wiring method. Quite a new Article.
Article 726, Class 4 Fault-Managed Power Systems. The new provisions may not be revolutionary, but what industry may be able to do with this new Article is impressive.
As revolutionary as this likely will be, Class 4 Fault-Managed Systems will not be introducing new technology. Technology such as this has been around for some time within different systems and standards. The novelty is how this new Article may facilitate the use of these technologies, which is important to the industry. Fault-managed power systems go by names such as Digital Electricity, Pulsed Power, Packet Energy Transfer, Smart Transfer Systems, and others. These patented technologies are some of the most remarkable examples of technological innovation the electrical industry and electrical codes may have seen in years.
So, what is it? Class 4 circuitry, Article 726 of the upcoming NEC, and its equipment listed to UL 1400 standards, consists of a transmitter and receiver. Easy. The transmitter, however, will monitor its output thousands of times per second and instantly disconnect power when a fault is detected. Forms of this technology will not even output any power until a digital handshake is completed with its receiver. This level of monitoring and speed of disconnection allows Class 4 circuits to operate at 450V peak or DC with no limitation on amperage (except a wire size limitation of 6 AWG) and provide a greater level of safety from electrical shock and fire than even a Class 2 circuit enjoys.
How does it work? A typical installation would begin with a listed Class 4 transmitter connected to power by means provided in other articles of the NEC. Class 4 wiring will extend from the transmitter to the listed receiver(s), which powers the connected loads outside the Class 4 circuits. It may not seem revolutionary, efficient, or cost-effective to have the transmitters and receivers between the load and overcurrent devices that would normally be there; however, this is a leading-edge change for many industries. For example, let us take a look at telecommunications. Telecommunication companies are in the process of rolling out 5G networks across the U.S. Currently, approximately 375,000 cell stations are providing 4G and LTE coverage. To deliver 5G, a much faster and higher bandwidth, it is estimated that 5,000,000 small cells may be needed*. Having this many locations, each connected to the utility with all the required equipment, is quite cost prohibitive. The power and voltage levels that Fault-Managed Systems can output allow for the central powering of these cells. Now, a telecommunication services provider can have one central power unit, the transmitter, connected to the utility, which can deliver safe electricity to dozens of small cells located thousands of feet away in any direction. The Fault-Managed System provides a more efficient installation, with the potential for cost savings by centralizing the power source. In addition, the outputted power would be so safe that a technician working on the system may one day simply short the feed wires together to cause the transmitter to shut down for maintenance.
Article 726 is in its first publication with this edition of the NEC. Given this, installation of Class 4 wiring is not permitted in a dwelling (NEC 726.12) nor in a hazardous location (rules struck through in pre-publication). Provisions included in the Article concern marking of equipment, non-interchangeability, fault management, mechanical execution of the work, separation of conductors, ampacity, listing requirements, and terminals and connectors. This wiring method will not be able to be mixed with different wiring types without separation or barriers, though it will be in cables with fiber optics and other Class 4 circuits. The fault management of these systems will detect a short circuit, line-to-line fault, ground fault, overcurrent, system malfunction, and any other condition that may pose an unacceptable risk of fire or electric shock. What did not make it to publication is fault management which shuts down the system when the lines are intentionally shorted, so that maintenance can be performed. Though this is not possible with existing systems, it shows the safety potential of these systems. Intentionally shorting a system with 450V AC or DC would present a major risk to equipment and life and be an incredibly dangerous thing to do. One day, the new technology may be so safe that intentionally shorting 450V will be the way to shut it off.
There are smart phones, smart TVs, smart everything. It’s time for smart electricity. Smart electricity has been the goal of the household or workplace of the future for many years. Class 4 is likely the start of the implementation of smart electricity that could upend electrical installations and equipment.
Take the household example. One day, when the installation of Class 4 circuits might be allowed in homes, there may no longer be a service panel in your home. Instead, it will be replaced by a Fault-Managed power transmitter. This transmitter could be capable of outputting various AC and DC voltages to circuits powering your entire home with electricity that could be safely touched. Not only that, receptacles and outlets will not output power until a digital handshake is made with a correct receiver, preventing electricity at the receptacle when not in use. This system is excellent for any home or daycare. Your TV, washer, dryer, stove, refrigerator – no end of devices – may no longer have power supply, but instead receivers capable of communicating with the transmitter. The wide use of Fault-Managed power transmitters means DC distribution will see a renaissance. Eliminating more than 100 power supplies in a modern home can remove the reactive power, leading to a power savings of 20%. This is where the revival of DC transmission and energy conservation come together.
Homes powered by Class 4 wiring methods have the potential to make electricity so safe that electrical fire and shock deaths would plummet. Perfect. This is what everyone involved in the electrical industry would love to see. It may be on the horizon.
Now, expand to a commercial property. Class 4 power using DC to power LED lighting, computers, and printers could remove so much reactive and zero sequence interference from the installation it may remove the need for zero-sequence filters, zig-zag transformers, and eliminate the overloading and burning of neutral wires. The potential power savings to these businesses alone could justify the conversion to Class 4.
Why is improved safety revolutionary? For many years, electrical safety was implemented by limiting total power and voltage to curb fire and shock hazards. Where did this leave systems that require greater amounts of power? In many ways, it led them to simply be more dangerous, and we accepted that. Everyone has a greater fear of 277V to ground than 30V limited to 100VA. We have just accepted a system that could not provide the same level of safety to these more powerful circuits. With Class 4 Fault-Managed power though, the 450V circuit with 6 AWG wiring may be even safer than that Class 2 circuit. Since only a very small portion of the population ever uses or works with greater than 450V, these new systems could upend the electrical safety industry one day. With the first edition of Article 726, all that is needed is time: time to implement these systems and develop new standards covering ever-greater product types and installations.
The future may be a long way off. Households with entire Class 4 wiring seem like a dream. Excitingly, the new NEC issue may have taken America’s first step in that direction!
*“Powering the Future Everywhere for Everyone.” January 2021, EnerSys
Kevin Smith, is a Senior Technologist, Field Evaluations and Verifications, with CSA Group.
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