Arc Flash, Coordination and Short Circuit Study and Its Five-Year Update at an Industrial Technology Campus, Houston (2020 and 2025)

NFPA 70E^® asks for an arc flash study to be updated at least every five years, or sooner when the system changes. At an industrial technology campus in Houston we did the original study in January 2020 and the update in March 2025.

The system

The campus takes one utility feed at 35 kV, stepped down to 4.16 kV by a single 3,750 kVA transformer, and distributes at 4.16 kV to substations that serve mixed-use buildings, including high-bay areas, at 480 V and below. There is one on-site generator. Protection is mostly fuses and non-settable breakers, with a single relay at the service point. Because the campus can be run in several ways, the model has six scenarios for different system configurations, and the labels use the worst case for each bus.

2020 and 2025

The 2020 model, built from one-lines, walkdowns and utility data supplied by the electrical contractor and checked by us on site, had 318 buses, nearly all at 480 V, with 13 at 4.16 kV. Seven buses were above 40 cal/cm², the highest about 77 at a high-bay substation.

The 2025 update, built from our own walkdowns and utility data, had 445 buses: 353 at 480 V, 65 at 208 V and 17 at 4.16 kV. The model grew at both 480 V and 208 V, with many more 208 V panels than before. Ten buses were above 40 cal/cm², the highest about 101 at the secondary of a high-bay transformer, and 26 were above 8. With few settable devices on site, neither study proposed setting changes. Where breakers or cables could not be reached, breakers were modeled with no trip function and cable sizes were estimated, both conservative choices.

Above 40 cal/cm², arc rated clothing is not considered enough, so those locations call for de-energized work. Five years of additions made the model bigger, and the update is how those changes reach the labels.

Related services

For the modeling and labels, see our arc flash study services. The field data comes from walkdowns and as-built drawings.