The rationale for change
While Article 220.12 has changed little since its NEC adoption in 1971, technology and sustainability initiatives have greatly advanced. Because of energy-efficient technologies for structures, LEED and other energy conservation efforts and energy codes and standards updates, the NEC needed to create parity.
Industry chatter regarding the size of service entrance equipment in relation to actual load, transformers and the like has been heard for at least the last two code cycles. Industry professionals realized that energy-efficient technologies had advanced to a point where load calculations were suspect of being grossly overestimated. Some in the industry claimed load calculation results no longer represented what happens in real-world applications thanks to technologies that use less energy, such as LED lights, fluorescents, high-efficiency transformers and variable frequency drives. Lower energy footprints impact the load calculations used to determine branch circuit size, feeders and everything else associated with power delivery, thus prompting the NEC to make changes that better ensure safety.
The basis of ASHRAE alignment
When many structures are built, ASHRAE requirements adopted by a state or local jurisdiction dictate VA per square foot, and builders may not exceed those requirements. However, CMP2 understood that not every jurisdiction adopts the latest ASHRAE standard. Some states use older ASHRAE requirements, and some jurisdictions don't adopt the requirements at all. This played a factor in the language included in the NEC.
Lower VA per square foot values influence smaller feeder and service sizes, which, if incorrect, could be very expensive to fix after the fact. NFPA members looked at different types of buildings and ASHRAE research data. The task force associated with this effort plotted VA curves for buildings of various sizes. To gain consensus and achieve change, the NEC lowered the VA values somewhat to account for those jurisdictions that do not adopt the latest version of ASHRAE standards or other energy codes. A compromise was reached in using the 2000 version of ASHRAE 90.1 as the uniform reference for VA values.
Financial impacts and safety implications
Some industry professionals reported that, when placing an ammeter on a structure’s service conductors, load currents showed a considerable margin between capacity and actual usage. Facilities typically consume less power due to higher-efficiency lighting equipment that’s installed and conservative factors that design engineers may use to ensure future capacity for growth. (Energy-efficient solutions are not required by the Code but are installed because of the energy savings they offer.)
I believe it’s important to include right-sized services in structures that meet design goals driven by customer wants and needs. The Code changes will offer financial relief for electrical infrastructures by foregoing equipment that’s not needed—but the design engineer must always keep a close eye on the needs of the customer. The changes help the design engineer reduce the size of electrical distribution equipment where permitted by the design goals. This could translate into less wire and other related gear. With that, I hope a focus on providing safety technologies for our electrical workers will grow. Funding originally intended for power distribution can be reallocated to safety solutions for branch, feeder and service entrance equipment.
A thought on using the Code as a design guide
NEC Article 90 states that the Code should not be used as a design reference. Language in Article 220.12 exemplifies why. As mentioned, there’s an informational note attached to 220.12. It states, “The unit values of Table 220.12 are based on minimum load conditions and 100 percent power factor and may not provide sufficient capacity for the installation contemplated." In essence, this means guidelines may not be sufficient for an installation. So, while the installation may be safe, it may not turn on because there isn’t enough power to serve the load.
In my opinion, designers must focus on customer wants and create load calculations based on a distribution system’s current and future needs. Many designers look to the Code before creating their designs, but they should do the opposite. I encourage all planners to meet customer wants and needs first and then check their designs against the Code to assure alignment.