NFPA Journal

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The calculation of electrical loads is one of those areas in the National Electrical Code® (NEC®) that has remained the same for many cycles. The standard numbers in Table 220.12—which are expressed as volt-amperes per square foot, or VA/ft2—have remained unchanged for as long as most of us can remember. The majority of the electrical industry accepted these values and, after all, it’s not like electrical installations were being undersized. Everything seemed to work well when using these values.

However, some folks in the electrical industry weren’t satisfied with this. As LED lighting became mainstream and utilization equipment became more energy efficient, a growing number of people questioned whether these values should be revisited. The Fire Protection Research Foundation embarked on a project to take a look at just how accurate the traditional numbers are in modern building practices. The Phase 1 report, authored by Tammy Gammon Ph.D., P.E., was published in 2017 and was used in submitting many public inputs for the 2020 NEC. The report is online at nfpa.org/news-and-research.

In addition to the questions raised regarding whether the standard values are oversizing our electrical installations, questions were also raised as to whether this led to higher levels of incident energy. While it is true that larger equipment has higher trip values and requires larger conductors, which means lower impedance values, there are so many variables to the equation that it is difficult to say conclusively one way or the other. This is an area that needs more research and is part of the discussion in the Research Foundation project.

All of this has led to significant revisions being proposed to Article 220 in the 2020 NEC. Specifically, there have been major changes proposed to Table 220.12. Today, there are various energy codes enforced across the country that are based on data from case studies supporting various levels of lighting power density specific to the occupancy. Much of this data has been incorporated into ANSI/ASHRAE/IES Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings. The list of occupancy types in Table 220.12 has been revised to correspond with what is listed in the ASHRAE standard. It was also recognized that it might take some time to transition to this new list, which is why footnotes have also been added to explain how the old list corresponds to the new.

An additional revision worth noting is that dwelling units have been completely removed from the table and are now found in section 220.14(J). This is due to the fact that the traditional value of 3 VA/ft2 includes a general receptacle component to it. The ASHRAE table recognizes lighting density in a dwelling unit as 1.0 watt per square foot, but this value is for lighting only. Revising this value could lead to unintended consequences, which is why it has remained untouched. Lastly, a note was added to the table to clarify that when using the values to calculate lighting loads that are continuous, the 125 percent demand factor has already been applied to these values in the table. As a result, it is not necessary to then apply this demand to the calculated load.

In many cases these values have been reduced and in others they have increased depending on how the old occupancy class was reclassified. Of course, all of these changes are still preliminary as there is still the opportunity to make an amending motion on the floor of the annual NFPA technical meeting, scheduled for June in San Antonio, Texas. Provided there are no successful certified amending motions to this section, the second draft language should be the final product. This version will be available online at nfpa.org/70next after the April 5 posting date.

All of this happened because users of the NEC asked questions, which led to research, which led to data being presented, which ultimately led to changes to the code to adapt to a changing industry. This is the NFPA standards development process at work, and demonstrates the legwork that goes into getting a substantial revision through that process. If that initial question hadn’t been asked, though, we would still be using old values, many of which have been in place since the Great Depression. Stay involved, stay connected, and keep asking questions.

DEREK VIGSTOL is an NFPA technical lead, Electrical Tech Services.