What Is an Arc Flash Study?

An arc flash study is a power system analysis that calculates the amount of energy released at a piece of electrical equipment if an arcing fault occurs. The result tells you what PPE a worker must wear, how close they can safely get to energized parts, and what warning labels belong on the equipment.

It is not a visual inspection. It is an engineering analysis. You need a one-line diagram, equipment ratings, protective device settings, and available fault current data before the math can start. The study produces incident energy values in calories per centimeter squared, arc flash boundaries in inches, and PPE requirements tied to specific equipment and operating conditions.

NFPA 70E requires an arc flash risk assessment before anyone works on or near energized electrical equipment operating at 50 volts or above. For most industrial and commercial facilities, that means a formal engineering study conducted under IEEE 1584.

Why arc flash studies are required

An arc flash releases energy fast. Thousands of degrees of heat, a pressure wave, shrapnel, and molten metal. Workers have died from arc flash incidents in facilities where the equipment appeared to be off or safe to approach.

OSHA 1910.132 requires employers to assess workplace hazards and provide appropriate PPE. OSHA 1910.269 covers electrical power generation, transmission, and distribution. Both reference the need to assess electrical hazards before work begins. NFPA 70E fills in the specific methodology.

Facilities that skip the study are not just out of compliance. They are putting workers in front of equipment without knowing whether a Category 2 arc suit is adequate or whether the real exposure is closer to 40 cal/cm² and requires far more protection.

What the study process looks like

A complete arc flash analysis is not a single calculation. It is a sequence of engineering tasks that build on each other. Miss a step or use bad data and the results at the end are wrong.

One-line diagram

Every arc flash study starts with an accurate one-line diagram. This is a simplified electrical schematic showing how power flows from the utility through transformers, switchgear, feeders, and panels down to the loads. If the facility does not have a current one-line, the engineer has to build one. That alone can add days to a project.

Data collection

This is where most of the field time goes. Someone walks the facility and records the nameplate data for every significant piece of equipment in the system: transformers, switchgear, motor control centers, panelboards, and the protective devices controlling each of them. Cable lengths and sizes. Utility available fault current from the serving utility. Breaker and relay settings.

On a complex facility with hundreds of panels, this takes days. The data gets entered into power system analysis software like SKM PowerTools, ETAP, or EasyPower to build a model of the electrical system.

Short circuit study

Once the model is built, the engineer runs a short circuit study to calculate available fault current at every bus in the system. This feeds the arc flash calculations. The arc flash incident energy at a piece of equipment is a function of how much current can flow through an arcing fault, how long the protective device takes to open, and the working distance.

Protective device coordination study

The coordination study looks at how protective devices upstream and downstream respond to fault conditions. Faster clearing times reduce incident energy. Sometimes a breaker is set too slow because of a legacy setting nobody has reviewed in years. The coordination study finds those situations.

Arc flash analysis and labeling

With fault currents and clearing times established, the software calculates incident energy at each piece of equipment using the IEEE 1584 methodology. The output is a report with incident energy values, arc flash boundaries, PPE requirements, and warning labels formatted for installation on the equipment.

What data gets collected in the field

The field data collection phase is where arc flash studies slow down. A technician or engineer walks the facility with a camera and a clipboard, or a tablet, and records equipment data at every location. The table below shows the typical data points collected for common equipment types.

Getting this data accurately is harder than it sounds. Nameplates are dirty, faded, or in awkward locations. Previous electrical work may not be documented. Equipment has been swapped without updating the one-line. A study is only as accurate as the field data behind it.

This is the phase 70Ez addresses directly. Instead of hand-writing nameplate data or typing into a spreadsheet for later entry, technicians photograph each piece of equipment and the AI reads the nameplate and populates the data fields. The field team verifies. The data is organized by project and exports into the analysis software. What used to take days of transcription happens in the field.

How long an arc flash study takes

A small commercial building with a single utility service, one transformer, and a handful of panels can be completed in a few days. A large industrial facility with medium-voltage distribution, multiple substations, hundreds of MCCs, and complex relay schemes can take weeks.

The breakdown typically looks like this:

• Site walkdown and data collection: 1 to 5 days depending on facility size
• Building or updating the power system model: 2 to 10 days
• Short circuit and coordination studies: 2 to 5 days
• Arc flash calculations and label generation: 1 to 3 days
• Report writing and review: 2 to 5 days

Data collection consistently runs long. Facilities that have organized, accessible equipment documentation cut this phase significantly. Facilities with outdated records or missing information add days while the engineer tracks down what is actually installed.

How often arc flash studies need to be updated

NFPA 70E recommends reviewing the arc flash risk assessment at intervals not to exceed five years. That review determines whether the study is still valid or whether a new analysis is needed.

More importantly, an arc flash study should be updated any time there is a significant change to the electrical system. Adding a transformer changes available fault current. Replacing a breaker with a different frame or settings changes clearing time. Either change can shift incident energy values enough to make existing labels wrong.

Who performs arc flash studies

Arc flash studies require a licensed professional engineer in most states for the engineering sign-off. The field data collection work can be performed by qualified electrical technicians under engineering supervision.

Engineering firms that specialize in power systems are the most common source. Some electrical contractors have in-house engineering staff and offer arc flash studies as a package alongside construction or maintenance work. Testing companies and inspection firms also offer arc flash studies as part of broader commissioning services.

The engineering analysis software, the IEEE 1584 calculations, and the report are all the engineer's responsibility. But the quality of what comes out depends directly on the quality of the field data that went in.

Arc flash study vs. arc flash risk assessment

NFPA 70E uses the term "arc flash risk assessment." An engineering study under IEEE 1584 is one way to satisfy that requirement. The other approach is to use the PPE tables in NFPA 70E directly, without a study, for certain tasks.

The table-based approach is faster but conservative. It assigns PPE requirements based on the task rather than the actual incident energy at the specific equipment. For facilities with modern, well-coordinated protective devices, the actual incident energy is often much lower than the table would suggest. A formal arc flash risk assessment based on an engineering study gives more accurate results and can justify lower PPE requirements where the system supports it.

Large industrial facilities almost always commission a full engineering study. The PPE savings and the ability to label equipment with actual incident energy values make it worthwhile.

The cost of getting it wrong

An arc flash study with bad input data produces wrong results. Labels that understate the hazard. PPE requirements that leave workers underprotected. The study passes the compliance checkbox but does not protect anyone.

The most common source of bad data is the data collection phase. Transposing a digit in an impedance value. Recording the nameplate from the wrong transformer. Missing that a breaker was replaced with a different model. These errors are easy to make when data collection means hand-writing numbers from a dirty nameplate in a poorly lit MCC room.

Modern field data collection tools reduce that error rate by capturing nameplate images and having software read them, rather than relying on a person to transcribe correctly under field conditions.