Arc Flash Study Across Nine Utility Feeds at a Mine and Mill, Marble Falls (2026)

In 2026 we completed an arc flash, coordination and short circuit study for a mine and mill in Marble Falls, in the Texas Hill Country. Client details are confidential.

Nine feeds, three units

The site has mixed-use spaces and nine utility feeds spread over three units. The first unit is the mine. Three utility drops there serve the underground mine, and three more serve the mine motor control center, the mine air compressor station and the mine office and training room.

The mills

The second unit takes one utility drop to three pad-mounted transformers. A 2,500 kVA transformer feeds four mill motor control centers, a 1,500 kVA unit feeds two more and the air compressor station, and a 750 kVA unit feeds four others. The third unit has three drops: the main office and an oil shed warehouse each drop to a 200 A safety disconnect, and the mill drops to two 2,000 kVA pad-mounted transformers that feed three more mill motor control centers and a third air compressor station. Each transformer size sets a different fault level at the gear below it, so every lineup has its own result.

Data from the walkdowns

Our engineers collected the system data on site, and the electric cooperative that serves the plant provided the utility data. Where a breaker could not be accessed, it was modeled without a trip function. Where a cable could not be traced, we assessed the size it would need for its load. Where needed, data was reviewed against IEC 60076-5 to keep the assumptions bounding and conservative. Typical enclosure and bus gap dimensions from IEEE 1584-2018 were used instead of opening energized equipment to measure it.

The calculations

The model was built in ETAP 26.0.0. We ran single-phase and three-phase duty and maximum short circuit cases at the utility feeds, switchgear, switchboards, motor control centers and panelboards, and checked the rated short circuit capacities reported to us. Equipment duty follows ANSI C37.010, and low-voltage breaker interrupting ratings follow C37.13 and UL 489. Incident energy follows IEEE 1584-2018 and NFPA 70E-2024, with the arcing time capped at 2 seconds. No critical items were identified. The one required action was to confirm the breaker settings against the settings report.

Hill Country work

What a study includes is described on the page for our arc flash study services. Recurring electrical work in the same region is the subject of our grounding and infrared program in the Hill Country.