Codes and Standards

NEC changes enhance resiliency

The 2020 edition of the National Electrical Code added changes to improve resiliency electrical system design

By John Yoon, PE, LEED AP ID+C; McGuire Engineers Inc., Chicago December 21, 2020
Figure 6: Installation of generators to support mission critical and health care facilities is common. However, their use is expanding to address concerns regarding the reliability of electrical utility sources. The 2020 National Electrical Code now requires that all stationary generators be listed in accordance with the applicable standard, UL 2200. Courtesy: McGuire Engineers

 

Learning Objectives

  • Understand the basic objectives of resilient electrical system design.
  • Identify changes in standard design practices that address resiliency.
  • Review changes in the 2020 National Electrical Code to help ensure that resilient electrical systems are safe.

NFPA 70: National Electrical Code represents the minimum acceptable standard for electrical installation in most jurisdictions within the United States. The code is revised every three years, with the most current version being the 2020 NEC. While most changes are intended to improve the usability of the code, there are a handful of changes that are intended to address evolving design practices such as those associated with resiliency in the built environment. These types of risk assessments are commonplace in the mission critical and health care industry.

However, the concepts of risk assessment and resiliency is relatively new in most other area of building design and construction. When evaluating resilient design practices in general, many government and industry organizations refer to four key characteristics, the “Four Rs” of resilience.

  • Robustness: The ability to resist an external disruptive event of defined magnitude without failure.
  • Redundancy: The ability to substitute alternate resources should the primary resource fail because of that external event.
  • Resourcefulness: Being adaptive in the response to an incident.
  • Rapidity: The ability to quickly respond to prevent further degradation or recover after an incident. This is important if you should fail trying to accomplish the previous three items.

Resiliency in electrical design

Based on 2018 U.S. Energy Information Administration data, nationwide, electrical utility customers experience average power interruptions totaling roughly two hours per year. While the length of time is necessarily not surprising, what is surprising is that this is only for causes other than major events. Once major events are factored in, the national average in 2018 increased to nearly six hours. Areas with higher potential for extreme weather, such as coastal states, can be significantly higher than this national average.

For example, North Carolina customers averaged 30 hours of power interruption compared to 1.5 hours in South Dakota. Furthermore, this number is a weighted average called the System Average Interruption Duration Index. SAIDI considers all customers within a given service area, not just those who had experienced an outage. For utility customers that experience outages, the total year duration will be higher. So, if that source of power is unreliable and extended outages are expected, how can electrical distribution systems be specified to ensure a minimal level of disruption and continuity of service?

Resilient electrical design focuses on the risks associated with utility level disturbances and associated mitigation solutions. Strategies include specification of surge protective devices to shunt transient voltages, on-site power generation such as photovoltaic systems and generators and energy storage systems, to name a few. These increasing common design solutions address robustness and redundancy requirements for a utility source, but what mechanisms exist to ensure that these solutions are safe?

Figure 1: Two photovoltaic systems on the rooftop of the Zonatherm facility in Buffalo Grove, Ill., have a total capacity of 185.1 kilowatts direct current power. Both systems use 340-watt PV modules and 15-kilowatt inverters. Panels are mounted on a 10-degree flat roof mounting system. Courtesy: Zonatherm

Figure 1: Two photovoltaic systems on the rooftop of the Zonatherm facility in Buffalo Grove, Ill., have a total capacity of 185.1 kilowatts direct current power. Both systems use 340-watt PV modules and 15-kilowatt inverters. Panels are mounted on a 10-degree flat roof mounting system. Courtesy: Zonatherm

Changes in the 2020 NEC

While resiliency is often considered a societal level concern, building codes such as the 2020 edition of the NEC focus on more immediate risks, the inherent hazards of distributing electrical power within a building. At times, these two goals can seem to be diametrically opposed. Resilient design typically focuses on ensuring uptime and continuity of service, while the NEC in a worst-case scenario ensures safety by interrupting the flow of power in an abnormal operating condition such as an overload or short circuit. However, a well-designed system should be both safe and reliable.

As technology standards emerge and new design practices gain acceptance, the NEC has changed accordingly. The NEC is an evolving consensus-based code that is regularly updated on a three-year cycle. Anyone can submit a proposal for change or a public comment. Those proposed changes are then forwarded to the appropriate technical committee for evaluation and a subsequent public review. For those interested in the details of the decision-making process, information including who submitted the proposed revision, statement of problem and substantiations and reasons for acceptable or rejection by the rule-making committee are available on NFPA website. The substantiation statements often include empirical information based on real world experiences with new technologies.

While most code changes are relatively minor edits to improve its usability, there are still numerous changes that significantly impact how electrical systems are designed. The beginning of every version of the NEC includes a summary of technical charges. This summary itemizes every single revision within the code. In the 2020 NEC Handbook, this list is 73 pages long. There are more than 100 individual changes to the definitions in the Article 100 alone. Even if the scope of this article was limited to only changes associated with resilient design practices, it would be impractical to summarize all of them here. As such, the focus will be on general changes that are most representative of the overall direction of code changes pertinent to the four aspects of resiliency.

Figure 2: National Electrical Code Article 625 has been renamed, laying the groundwork for future requirements associated with bi-directional electric vehicle charging equipment. Bi-directional EV charging is an example of an emerging technology that has the potential to improve the resiliency of electrical installations. Courtesy: McGuire Engineers

Figure 2: National Electrical Code Article 625 has been renamed, laying the groundwork for future requirements associated with bi-directional electric vehicle charging equipment. Bi-directional EV charging is an example of an emerging technology that has the potential to improve the resiliency of electrical installations. Courtesy: McGuire Engineers

Robustness: withstanding disruptive events

A common concern is the potential for damage to sensitive electronics and equipment cause by utility or weather-induced voltage transients. SPDs are valuable in helping ensure that an electrical distribution system can withstand those overvoltage conditions. However, the code did not mandate use of SPDs except in very specific situations. There are multiple revisions in the 2020 NEC related to SPDs that are changing that and would seem to telegraph the direction of future changes in the 2023 NEC.

Article 242, overvoltage protection: This is a new article in the 2020 NEC and is intended to provide general, installation and connection requirements for overvoltage protection devices. In the 2017 NEC, there were two related articles, 280 (surge arresters over 1,000 volts) and 285 (surge-protective devices of 1,000 volts or less). Article 242 replaces those two.

While the NEC has traditionally focused on overcurrent protection as defined in Article 240, it was recognized that overvoltage is also a significant hazard that should be addressed in a more comprehensive manner. The NFPA’s steering committees’ substantiation for this consolidation into a single new article following Article 240 is that it would provide a more user friend format with significantly improved clarity and usability.

Surge protection: The earliest requirements for SPDs originated several code cycles ago and with each subsequence revision of the NEC, their mandated uses have expanded. The earliest requirement was in the 2008 NEC when Article 708, critical operations power systems, included a requirement that SPDs be provided to protect loads connected to those systems. The critical nature of COPS justified the additional protective requirements. When Article 694, wind electric systems, was added in the 2011 NEC, SPD use was also mandated. Given that wind turbines are usual tallest structures in otherwise open areas, their use makes sense to protect against the effects of lightning.

Figure 3: This shows a decommissioned flooded cell battery rack for a uninterruptible power supply system. Revisions in the 2020 National Electrical Code have helped clear confusion regarding the differences between energy storage systems and UPS systems. Courtesy: McGuire Engineers

Figure 3: This shows a decommissioned flooded cell battery rack for a uninterruptible power supply system. Revisions in the 2020 National Electrical Code have helped clear confusion regarding the differences between energy storage systems and UPS systems. Courtesy: McGuire Engineers

Subsequently, in the 2014 NEC, a requirement was added in Section 700.8 that a listed SPD be installed on all emergency system switchboards and panelboards. Furthermore, in the 2017 NEC, this SPD requirement was extended to also include fire pump controllers in section 695.15 and elevators that are considered an emergency system load per section 620.51(E).

Due to the critical natures of the systems described in those NEC articles, the application of SPDs seems logical. However, the 2020 NEC introduced a new requirement for SPDs to be provided on all services at dwelling units. Section 230.67 states that the SPD must be an integral part of the service equipment or located immediately adjacent to it. The justification in NFPA committee’s statement included the following:

“The expanding use of distributed energy resources with electrical systems often results in more opportunity or greater exposure for the introduction of surges into the system.”

Currently, this requirement is limited to dwelling units. The original public comments received during the code making process proposed a much wider scope where SPDs would be required not just for dwelling units, but any electrical service less than 1,000 volts. It would not be unexpected if this expanded requirement were incorporated into the 2023 NEC.

Redundancy: providing alternate resources

If the reliability of an electrical utility service is suspect, the most logical solution is to provide an alternate source of power. This has long been standard design practice in the mission critical and health care industry where power interruptions have significant financial and safety implications. Those same industries are also highly regulated and typically have extensively engineered electrical distribution systems.

Figure 4: In this system disconnect switch for a large photovoltaic array, the ability to quickly de-energize an on-site power generation system in critical in ensuring the safety of first responders. The 2020 National Electrical Code has harmonized requirements for these types of disconnect devices across multiple articles in the Code. Courtesy: McGuire Engineers

Figure 4: In this system disconnect switch for a large photovoltaic array, the ability to quickly de-energize an on-site power generation system in critical in ensuring the safety of first responders. The 2020 National Electrical Code has harmonized requirements for these types of disconnect devices across multiple articles in the Code. Courtesy: McGuire Engineers

However, standby generators, PV and battery storage systems are becoming more common in much smaller installations. Industry standards and practices have evolved accordingly and are reflected in the following revisions to the NEC.

Section 445.6, listing of stationary generators of 600 volts or less: With the use of standby generators expanding well beyond traditional life safety and mission critical functions, it’s surprising to learn that there were no listing requirements associated with stationary generators in the 2017 NEC. The 2020 NEC rectified this situation by adding a section that requires that all stationary generators, 600 volts and less, be listed. The applicable standard in this case would be UL 2200, Stationary Engine Generator Assemblies. For highly customized and medium-voltage generators that are not listed by the manufacturer, those generators can be field labeled by a field evaluation body.

As the use of alternate sources of power increase, the likelihood of something going wrong also increases. The typical solution is to provide a means to quickly deenergize that system. Before the 2020 NEC, the requirement for that emergency disconnecting means was inconsistent or nonexistent. The 2020 NEC harmonized that requirements across multiple articles. All on-site energy generation and storage system must have a readily accessible means of emergency disconnect that is appropriately labeled so that its function can be easily identified by whoever would need to use that disconnect in an emergency. The follow code sections were modified with this new requirement:

  • Section 445.18(C): remote emergency shutdown for generators larger than 15 kilowatts.
  • Section 445.18(D): emergency shutdown in one- and two-family dwelling units.
  • Section 480.7(B): storage batteries – emergency disconnect.
  • Section 694.22(c)(1): wind electric systems – requirements for disconnecting means.
  • Section 706.15(A): energy storage systems – disconnecting means.
  • Section 690.12: rapid shutdown of PV systems.
  • Section 690.13: PV system disconnecting means.

Section 690.12 deviates slightly from those other sections. The revision emphasize that the intent of the requirement is to reduce shock hazard associated with a PV system specifically for firefighters who might be required to enter a building during an emergency condition. The 2017 NEC stated generically that this was for emergency responders, and not firefighters. The change is intended to narrow down who the rapid shutdown function is intended for.

The original generic term from the 2017 NEC could be interpreted as applying to police, utility workers or other similar personnel. Generally, firefighters cannot wait until the utility company arrives at the site to start fighting the fire. Oddly, this clarification was not included in Articles 445, 480, 694 and 706 where comparable hazards are present. Other changes in this section are intended to harmonize with a new product standard, UL 3741: Standard for Safety Photovoltaic Hazard Control. The listed products/methods for achieving proper rapid PV system shutdown as required by 690.12 are defined by the second edition of UL 3741, not the NEC.

With the addition of multiple new articles related to on-site power generation and storage in the 2017 NEC, there was significant confusion regarding overlapping scope between those articles. One such addition was Article 706, energy storage systems. Based on how the article was originally written, it could be interpreted as also applying to uninterruptible power supply systems. The revisions to the scope for this article in the 2020 NEC have clarified that it does not necessary apply to UPS system. The revision states that ESSs are primarily intended to both store and provide energy during normal operating conditions. Batteries in UPS systems are generally intended to provide power to a load only in the event of a power failure. This article was also revised to apply not just to permanent but also temporary ESS installations.

The 2017 NEC also introduced some confusion regarding the operational modes for on-site power generation and energy storage. The 2017 NEC added a definition for “stand-alone (islanded) mode” and a related Article 710: stand-alone systems. The original definition was not entirely clear in the context of another new Article 705: interconnected electric power production sources. The systems addressed by Article 705 are also commonly referred to as “microgrid systems.” In the 2020 NEC, all references to stand-alone (islanded) was removed and replaced with “island mode.”

There are now separate definitions in Article 100 for stand-alone system and island mode. The distinction here is that Article 710 usually refer to off-the-grid electrical systems, primarily in remote areas, where islanded mode is usually the primary mode of operation. The key distinction in the new definition for island mode is that it can apply to any energy generation or storage systems that is an interconnected system per Article 705, but is capable of operation when disconnected from primary external utility source, not just Article 710.

The island mode definition now references multimode inverters and both isolated and interconnected microgrids. These changes are consistent with IEEE 1547-2018: Standard for Interconnection and Interoperability of Distributed Energy Resources With Associated Electric Power System Interfaces.

Figure 5: Timely restoration of electrical power after a disaster often requires reuse of distribution equipment. However, reuse of equipment that has been exposed to flooding and fire, such as in this picture of sediment covered cable lug in a flood damaged switchboard, can cause additional hazards. The 2020 National Electrical Code includes additional guidance where reconditioned equipment can and cannot be used. Courtesy: McGuire Engineers

Figure 5: Timely restoration of electrical power after a disaster often requires reuse of distribution equipment. However, reuse of equipment that has been exposed to flooding and fire, such as in this picture of sediment covered cable lug in a flood damaged switchboard, can cause additional hazards. The 2020 National Electrical Code includes additional guidance where reconditioned equipment can and cannot be used. Courtesy: McGuire Engineers

Resourcefulness: being adaptive

Emerging technologies bring new solutions to old problems. Generators, PV and battery storage are becoming common solutions to the problem of electrical utility instability. However, one emerging technology that has the potential to disrupt those traditional solutions are battery electric vehicles. To provide extended driving range, many EV manufacturers now offer battery capacity options that exceed 80 kilowatt hours. As the adoption of EVs in the automotive marketplace increases, tapping into this energy storage to increase energy resiliency becomes extremely attractive. Telsa alone has produced more than a million vehicles representing a total potential energy storage capacity near 75 gigawatt hours.

Article 625: electric vehicle power transfer systems: The title of the article was changed from “electric vehicle charging systems.” There are numerous changes in this article to harmonize with new UL listing requirements for EV chargers. However, the most significant change in this article was the inclusion of rules related to power export and bidirectional current flow equipment. Traditionally, EV chargers where unidirectional and functioned only to charge the EV’s battery. The changes in the title and associated article text recognizes that electric vehicles could eventually function as energy storage systems.

Industry standards do not yet exist to allow EVs to function as an ESS. However, from a resiliency standpoint, the potential to export power from an EV’s batteries back to the building or utility grid is extremely attractive. These changes are seen as laying the groundwork to allow for this functionality once the appropriate industry standards are established and EV manufacturers start to incorporate bidirectional chargers into their vehicles.

Figure 6: Installation of generators to support mission critical and health care facilities is common. However, their use is expanding to address concerns regarding the reliability of electrical utility sources. The 2020 National Electrical Code now requires that all stationary generators be listed in accordance with the applicable standard, UL 2200. Courtesy: McGuire Engineers

Figure 6: Installation of generators to support mission critical and health care facilities is common. However, their use is expanding to address concerns regarding the reliability of electrical utility sources. The 2020 National Electrical Code now requires that all stationary generators be listed in accordance with the applicable standard, UL 2200. Courtesy: McGuire Engineers

Rapidity: recovering quickly, safely

Following fire, flooding and seismic events, it is commonplace for electrical distribution equipment to be reconditioned and reused. This is often due to budgetary or schedule restraints. The term “reconditioned equipment” was referenced in multiple locations in NEC, but no formal definition was given for it until the 2020 NEC. For clarity and consistent enforcement, a definition is required so that there is a clear distinction between reconditioning and simple one-for-one part replacement and routine maintenance. This differentiation from rebuilt, refurbished or remanufactured equipment is important because it is interrelated with changes in several sections of the code. These changes harmonize with National Electrical Manufacturers Association’s policy on reconditioned electrical equipment. This policy is reflected in the following NEMA standard guideline publications:

  • Evaluating Water-Damaged Electrical Equipment NEMA GD 1-2019.
  • Evaluating Fire- and Heat-Damaged Electrical Equipment NEMA GD 2-2016.
  • Evaluating Earthquake Damaged Electrical Equipment Guide NEMA GD 3-2019.

NEC Section 110.21(A)(2), equipment markings – reconditioned equipment was expanded so that when reconditioned equipment is used, there are special labeling requirements that apply to that equipment. The original manufacturer’s listing marks be removed from the equipment and replaced with new labeling that identifies it as reconditioned, the organization responsible for the reconditioning and the date of reconditioning.

The justification for this requirement is that the original manufacturer and/or the original third-party certification organization cannot reasonably be expected to certify the performance of any equipment that has be substantially modified or reconstructed. This responsibility must then fall to the firm that is reconditioning that equipment. Ultimately, this new labeling requirements provide traceability and accountability for the safety and functionality of any reconditioned equipment. The logical follow up question is, “How do you determine if the firm responsible for reconditioning is appropriately qualified?” UL has a Rebuilt Equipment Certification Program to help determine if a firm has the necessary technical skills and resources to safely refurbish equipment, consistent with UL safety requirements.

The new Section 240.88, reconditioned equipment, has guidelines regarding the use of reconditioned equipment. Oftentimes, disaster recovery efforts necessitate the use of reconditioned equipment. However, there were no specific rules regarding the use of such equipment in the 2017 NEC. There is a concern regarding the functionality and safety of such equipment if no applicable requirements exist within the NEC.

As previously mentioned, NEC now follows NEMA GD-1, GD-2 and GD-3 standards as industry-accepted guidelines regarding what type of equipment can be reconditioned. Six different locations within the NEC were modified accordingly to allow reconditioned equipment. More importantly, 15 additional sections were added or revised to prohibit the reconditioning of certain types of equipment. In general, any device that cannot be readily disassembled, has solid state electrical components or has intricate mechanisms may not be reconditioned. This includes transformers, ground-fault and arc-fault circuit interrupters, fuses and molded case circuit breakers, among other devices.

As technology and standard design practices change to address societal level concerns such as resiliency, the NEC changes as well. While some steps in that evolution may be a bit bumpy, it should be remembered that the NEC is a living document that evolves in response to new electrical hazards. The ultimate goal in all of this is to help ensure that electrical installations are safe.


John Yoon, PE, LEED AP ID+C; McGuire Engineers Inc., Chicago
Author Bio: John Yoon is lead electrical engineer at McGuire Engineers. He is a member of the Consulting-Specifying Engineer editorial advisory board.