Arc Flash Analysis & Compliance

An arc flash study calculates the incident energy available at each point in your electrical system where someone may work on or near energized equipment, and produces the labels and PPE guidance that OSHA and NFPA 70E require. If you want the background first, start with what an arc flash is and how to read the label. This page is about how the work is actually performed and what you receive.

What the Study Covers, and What It Does Not

IEEE 1584-2018 is an empirically derived model with a stated range of validity. It applies to three-phase AC systems from 208 V to 15 kV, with bolted fault current between 700 A and 106 kA, and conductor gaps within the ranges given for each equipment class. Systems or conditions outside that envelope are not covered by the model, and any engineer telling you otherwise is extrapolating past the data.

That matters in practice more often than people expect. Single-phase systems fall outside the scope of IEEE 1584. So do DC systems, which require a separate methodology. Where your facility has equipment outside the model range, the study says so explicitly and explains what basis was used instead, rather than quietly producing a number that looks like the others.

Every study I issue also states its assumptions and limitations in writing: which devices were field verified and which were carried from existing documentation, which equipment was inaccessible or could not be de-energized at the time of the field investigation, and which values came from the utility. You should be able to read the assumptions page and know exactly how much of the result rests on observation and how much rests on documents someone handed me.

How the Study Is Performed

1. Field Data Collection

Every study begins with a field investigation of the distribution system. I collect nameplate data from transformers, switchgear, switchboards, panelboards, motor control centers, and protective devices, including breaker types and trip settings, fuse manufacturer and class, conductor sizes and lengths, and system configuration.

Fuse class matters here more than most people realize. A 200 A Class RK1 and a 200 A Class RK5 are both "a 200 amp fuse" on a shelf, and they produce different clearing times, different incident energy, and different availability of a listed series combination rating. Fuses get recorded by manufacturer and class, not just ampere rating.

Where one-line diagrams exist, I use them as the starting point and verify them in the field. Where they do not exist or no longer reflect the installation, developing them is part of the scope.

2. Utility Coordination

Available fault current and X/R ratio at the service are requested directly from the serving utility rather than estimated. Utility response times vary and are often the longest lead item in the schedule, so that request goes out at the start of the project rather than when the model is ready for it.

3. System Modeling

Modeling is performed in SKM Power*Tools or EasyPower. The model includes all significant impedance sources from the utility service through the last point of worker interaction: utility contribution, transformers, cables, buses, and protective devices.

If you already have a study and can provide the native model file in either platform, I can usually work from it rather than rebuilding from scratch. That is a meaningful cost difference on a renewal, and it is worth asking your previous engineer for the native file even if you are not ready to commission an update yet. A report PDF alone does not let the next engineer verify anything.

If your specification requires a particular platform, say so in the RFP. Working in both means a software requirement is usually a scoping question rather than a disqualifier.

4. Short-Circuit Analysis

Before incident energy can be calculated, a short-circuit analysis determines available fault current at every bus. This is also where equipment evaluation happens: comparing calculated fault current against the interrupting rating of each protective device and the short circuit current rating of each assembly.

This step frequently produces findings that have nothing to do with arc flash. A device applied above its interrupting rating is a separate failure mode from an arc flash hazard, and a low incident energy label tells you nothing about it. Both get reported.

5. Protective Device Clearing Times

Time-current characteristics for every device in the path are modeled to determine actual clearing time for an arcing fault at each location. Arc duration is one of the two primary drivers of incident energy, so this step governs the result more than anything else in the study.

IEEE 1584-2018 also requires evaluating arcing current variation, because actual arcing current in the field can be lower than the calculated value, which can push the fault below a device's instantaneous region and dramatically increase clearing time. The governing worst case across evaluated conditions is what goes on the label.

6. Incident Energy Calculations

For each location the study determines:

• Incident energy at the working distance, in cal/cm²
• Arc flash boundary, the distance at which incident energy falls to 1.2 cal/cm²
• Limited and restricted shock approach boundaries
• Arcing fault current and clearing time, so the result is auditable

Line side and load side of service mains are evaluated separately, since clearing on the line side depends on the utility's primary protective device and often produces a materially higher number than the bus behind it.

7. Labels

Labels are produced for every analyzed location per NFPA 70E 130.5(H) and NEC 110.16, printed on durable adhesive-backed material and shipped to your facility. Installation is by facility personnel unless arranged otherwise, because label placement depends on access and equipment condition that are better judged on site.

Labels state incident energy and arc flash boundary using the incident energy analysis method. If your existing labels use NFPA 70E PPE categories, the new labels replace them rather than supplementing them. Mixing the two methods across one facility is how people end up selecting PPE off the wrong basis. For what must appear on each label, see the NEC 110.16 label requirements guide.

SAMPLE

8. Sealed Engineering Report

The deliverable is a sealed engineering report containing updated one-line diagrams, short-circuit results, equipment evaluation identifying any device or assembly applied above its rating, incident energy results for every analyzed bus, PPE requirements, the stated assumptions and limitations, and mitigation recommendations where incident energy can practically be reduced.

On a renewal the report also includes a bus-by-bus comparison against the previous study, with the reason for each material change. You should be able to see what moved and why, not just receive a new set of numbers.

Arc Flash Mitigation

Calculating the hazard is only useful if something can be done about it. Where incident energy is high enough to warrant it, the report identifies practical reductions:

• Protective device setting optimization. Adjusting trip settings or adding instantaneous overrides to shorten arc duration. Often the cheapest fix available.
• Main fuse or breaker resizing. Main devices are frequently sized well above transformer full load current. Correcting that can move a location out of the arc flash suit range entirely.
• Current-limiting fuses. Replacing standard fuses with current-limiting types to reduce let-through energy.
• Zone-selective interlocking. Communication between devices to accelerate upstream clearing.
• Arc energy reduction per NEC 240.87. Required on certain devices and worth evaluating against what you already have installed.
• Maintenance mode settings. Temporary reduced settings applied during energized work.
• Remote racking and operation. Engineering controls that remove the worker from the boundary during switching.

Where a change affects coordination with adjacent devices, that is evaluated before it is recommended. A mitigation that creates a selectivity problem is not a mitigation.

What I Need From You

Studies move faster and cost less when this material is available at kickoff:

• Existing one-line diagrams, even if outdated or marked up
• Any prior arc flash or short-circuit study, and the native model file if one exists
• Panel schedules
• Utility account numbers for the fault current request
• A list of electrical system changes since the last study, including spare capacity that was put into service
• Site access arrangements, and whether any equipment can be de-energized during the field visit

None of it is a prerequisite. Missing information gets handled with conservative assumptions, documented as such. But the more that exists, the less of the result rests on assumption.

Working Directly With the Engineer

You work directly with Nick Zech, PE. There is no account manager between you and the person doing the calculations, and the person who walks your facility is the person who seals the report.

• Licensed Professional Engineer in 17 states, with additional states available by comity.
• Studies performed to IEEE 1584-2018, NFPA 70E, and the applicable NEC edition for your jurisdiction.
• Arc flash and power system studies are the practice, not a service line attached to something else.
• Fixed-fee proposals with scope and exclusions stated in writing before you sign.

Related services: short circuit study, protective device coordination study, and electrical capacity and load studies.