Arc Flash, Coordination and Short Circuit Study, With an Infrared Scan, at an Electronics Facility, Austin (2022)

An electronics company facility in Austin needed an arc flash study and an infrared scan of the same equipment, and in late 2022 we did both on one set of site visits.

A model built from the field

We drew the one-line ourselves from a walkdown. The building has one utility service: a utility transformer feeds an outdoor 600 A breaker, which feeds the main distribution panel at 480 V, and from there 480 V panels and transformers serve 208 V panels. The model also includes a standby generator. We modeled all of it in ETAP^®, 27 buses in all, with cable lengths and sizes, transformers, panels, transfer equipment and the generator, and ran the incident energy per IEEE 1584-2018 for two cases, normal utility service and generator supply. Where the utility could not supply its fault data, we used conservative values based on IEC 60076-5.

Where the energy is

The two highest values, about 49 and 50 cal/cm², were at the 480 V service ahead of the outdoor breaker: the transformer secondary and the breaker enclosure. Those sit above the 40 cal/cm² level where no arc rated clothing is considered adequate, so work there should be done de-energized, which at a service point means coordinating with the utility. Inside the building the numbers dropped quickly; the 208 V panels peaked near 9 cal/cm², and most buses were far lower. No device setting changes were needed, and the report asks that the settings in the field be confirmed against the settings document.

The infrared scan

On November 28 we scanned 12 pieces of gear, from the main panel to the 208 V panels and the outdoor main. Nothing was outside the expected temperature range. Control power transformers can look hot in a thermal image, and that is normal. The only note was that the main panel trip settings were not visible.

Related services

For the modeling, see our arc flash study services. The scan is described under infrared inspections.