What is an arc flash study?
An arc flash study calculates the thermal energy released if an electrical fault arcs inside equipment, and produces the labels and boundaries that tell electricians what protective equipment they need to work on it. It is built from a short-circuit study and protective-device coordination data, and it is required in practice by workplace electrical safety standards — NFPA 70E for the work practices, with the equipment labeling anchored in the electrical code. Any facility with significant distribution equipment needs one; insurers and safety auditors ask for it by name.
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What the study calculates
For each piece of equipment — switchgear, panelboards, MCCs, disconnects — the study determines the available fault current, how fast the upstream protective device clears a fault at that location, and from those two, the incident energy at the working distance: the number that decides the PPE category. It also sets the arc flash boundary, the distance at which the energy drops to a survivable level for unprotected skin. Clearing time is the lever most people miss: a modest fault current cleared slowly can deliver more energy than a large one cleared fast, which is why the study and the coordination of the devices cannot be separated.
What it needs as input
The study is only as good as the one-line diagram underneath it. Inputs: the utility's available fault current at the service, transformer sizes and impedances, conductor lengths and sizes between equipment, and the exact protective devices — breaker models, fuse types, trip settings — installed at each level. On existing facilities, that data comes from a field survey, because panels accumulate undocumented changes. A study built on assumed settings produces labels that describe a building that does not exist; the field verification is not overhead, it is the study.
Labels, and what happens after
The visible output is the equipment label: nominal voltage, arc flash boundary, incident energy or PPE category, and the study date. The operational outputs matter as much: a report identifying locations where incident energy is dangerously high and the engineering fixes — adjusted trip settings, different fuse classes, current-limiting devices, maintenance-mode switches — that bring it down. Settings changes must be applied in the field and the study updated, on a review cycle (five years is the standard interval, and sooner after any distribution change). A study filed and forgotten decays into fiction as the building changes around it.
When you need one
New construction with substantial distribution, service upgrades, tenant work that changes the electrical distribution, and any facility formalizing an electrical safety program. Also after utility changes: a new service transformer changes the available fault current everywhere downstream. Torch performs arc flash, short-circuit, and coordination work as one study package — the three share the same model — and delivers the labels, the report, and the recommended settings, sealed by a licensed PE. Send the one-line if you have one; if you do not, the field survey is step one and we will scope it.
The bottom line
An arc flash study turns your distribution system into numbers an electrician can dress for: incident energy, boundaries, and labels per equipment. It stands on a verified one-line and current device settings — and it expires as the building changes.
Torch Engineering PLLC · (480) 490-0064 · info@torchengineering.com — PE stamping backed by Apex Grid Engineering.