A DC arc-flash study needs enough verified information to model the current that can reach an arc, how long protective devices take to clear it, and how the worker and equipment are positioned. Start with a current DC one-line diagram and a list of equipment, tasks, and operating configurations. Then collect source short-circuit data, cable and bus impedances, protective-device details, and task geometry. A qualified engineer must select and document a DC calculation method; IEEE 1584-2018 is a three-phase AC guide and does not calculate DC arc flash.
Begin by defining the study boundary and scenarios
Before requesting technical numbers, write down exactly what the study covers. The same installation can have materially different arc conditions when a charger is connected, battery strings are paralleled, or a maintenance bypass is closed. A useful scope tells the engineer which equipment and work activities are included, which operating states must be modeled, and what the final report must contain.
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Record the facility and equipment boundary
- Facility name and location, including the jurisdiction whose electrical-safety rules apply.
- Equipment names, identification numbers, physical locations, and the source-to-work-location path.
- Tasks to be evaluated, such as racking a battery, opening a DC switchboard, testing a bus, or replacing a fuse.
- Requested deliverables: calculation report, equipment labels, incident-energy values, approach boundaries, PPE recommendations, mitigation options, or a combination.
- The date of field data and the revision of drawings and settings used.
List every credible operating configuration
Provide a current DC one-line diagram showing normal and alternate paths. Identify parallel battery strings, chargers that can contribute current, rectifiers, photovoltaic or other DC sources, tie breakers, transfer equipment, and disconnect positions. Ask the engineer to include normal operation and credible maintenance configurations, not just the state observed during a single walk-through. A configuration that is rarely used can still govern a result if it produces a larger source contribution or a slower clearing time.
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Collect DC source information and available fault current
The engineer needs source data at the level of the potential arc, not merely the nominal voltage printed on a battery cabinet. NFPA 70E committee material in the 2026 first-draft report states: “Battery cell short-circuit current can be obtained from the battery manufacturer.” Treat that document as draft committee material, not as proof of the final edition adopted where you work.
Battery and other source records
- Source type, manufacturer, model, and nameplate voltage.
- For batteries: chemistry, cell count, string arrangement, nominal voltage, ampere-hour capacity, age or condition information available to the owner, and the manufacturer’s short-circuit-current data.
- Number of strings and how strings are connected in parallel for each operating scenario.
- Charger or rectifier make, model, rating, current limit, and whether it is connected, disconnected, or in a fault-support mode during each scenario.
- Other sources that can feed the same bus, including energy-storage converters or backfeed paths.
- Manufacturer data sheets and test documents, with their revision dates.
Do not substitute ampere-hour capacity for short-circuit current. Capacity describes stored charge; the current available during a fault also depends on internal resistance, interconnections, temperature, state of charge, and source controls. If a manufacturer does not provide a value, document that gap and have the qualified analyst select a defensible assumption or obtain a test or engineering estimate.
Model the path from source to the work point
Available current at the battery terminals can be very different from current at a remote panel or disconnect. Gather:
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- Cable conductor material, size, number of parallel conductors, insulation type where relevant, and installed length.
- Positive and negative conductor paths, bonding or return connections, and any intentional current-limiting components.
- Joints, switches, fuses, contactors, bus links, and other connections whose resistance or inductance is significant.
- Manufacturer impedance data for cables, bus assemblies, reactors, converters, or current-limiting devices when available.
NFPA material identifies DC circuit modeling as the best way to determine available short-circuit current at the point of the arc and says cables and other circuit impedances should be included. Give the engineer the drawings and measured lengths needed to calculate that point current. A fault-current value copied from a source nameplate without the intervening impedance can overstate or understate the arc input.
Provide complete protective-device and clearing data
Incident-energy estimates are highly sensitive to the time an arc persists. The study therefore needs the installed device identity and its actual operating behavior, not a generic “breaker” or “fuse” description.
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Fuse information
- Manufacturer, catalog or part number, voltage rating for DC use, interrupting rating, and fuse class.
- Quantity and series/parallel arrangement, including any current-limiting fuses upstream or downstream.
- Installation orientation and holder or switch-fuse assembly details that could affect the listed performance.
- Manufacturer time-current curves and total-clearing data at the fault currents calculated for each scenario.
Breaker, contactor, and electronic protection information
- Manufacturer, model, frame size, DC voltage and interrupting ratings, pole arrangement, and series-connected pole requirements.
- Trip-unit type and settings: instantaneous, short-time, long-time, ground-fault or other functions that can operate on the DC circuit.
- Current-limiting or electronic-control functions, firmware or setting revisions where applicable, and whether a charger controller limits fault current.
- Coordination or selective-tripping arrangements that change which device clears first.
- Maintenance, testing, and calibration records; photographs of labels and setting dials are useful field evidence.
Ask for manufacturer clearing curves or test data and identify the current at which the device is expected to operate. Field-check settings and device condition. If a curve is unavailable and an assumed clearing time is used, the report should identify the assumption, explain why it was selected, and show its effect on the result. A nominal device rating is not a clearing-time value.
Document equipment configuration and arc geometry
Source current and clearing time do not define exposure by themselves. The arc’s location, enclosure, electrode arrangement, and worker distance affect the energy that can reach a person.
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Equipment and enclosure details
- Equipment type, enclosure dimensions, construction material, internal compartments, and bus arrangement.
- Whether the task is in open air, behind a door or cover, or inside an enclosure with the door or cover open, closed, removed, or partially installed.
- Barriers, insulating components, shutters, shields, and temporary covers present during the task.
- Photographs and dimensional sketches showing the actual working configuration.
NFPA committee material warns that an open-air incident-energy calculation may understate exposure for work inside an enclosure. This is a method and PPE caution, not an automatic multiplier that can be applied to every result. The engineer must use a method whose enclosure assumptions fit the equipment or clearly state the limitation.
Electrodes, gap, and orientation
Record electrode orientation and the gap between conductors when those values are established or applicable to the selected method. Note whether a dimension was measured, taken from a drawing, or assumed. Include conductor shape, exposed length, and any tool or probe that can bridge conductors. If the study method does not use a particular geometry parameter, the report should say so rather than implying that an unmeasured value was known.
Worker position and working distance
For each task, document where the worker’s torso, face, and hands are expected to be relative to the potential arc. Working distance is measured from the prospective arc location to the worker, not simply from the enclosure door. California’s Appendix D identifies arc length, employee distance, fault current, and protective-device clearing time as calculation parameters and notes that equipment size and work distance matter when selecting the employee-to-arc distance. Use task-specific distances when a worker must reach into a cabinet or stand closer than the nominal front-of-equipment position.
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Separate owner-provided records from engineering judgments
A practical handoff distinguishes facts the facility can gather from assumptions that require a qualified analyst. This prevents an apparently precise spreadsheet from hiding an unverified input.
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|---|---|
| Current DC one-line, equipment IDs, locations, and task list | Whether the drawing represents all credible source paths and maintenance states |
| Battery, charger, rectifier, and converter nameplates and manufacturer data | Available short-circuit current at each arc location, including source impedance and contribution |
| Cable schedules, conductor sizes, lengths, bus details, and connection photographs | Electrical impedance model and whether omitted connections materially change the result |
| Fuse and breaker make, model, ratings, settings, curves, and maintenance records | Operating and total-clearing time at the calculated fault current, including coordination effects |
| Enclosure dimensions, door state, electrode measurements, and task photographs | Applicability of the chosen DC arc method to the geometry, enclosure, and electrode arrangement |
| Worker posture, access route, and proposed working distance | Calculation distance, hazard measures, labels, boundaries, and PPE recommendations |
What the report should disclose
Request a report that lets another engineer understand exactly what was modeled. At minimum, it should identify:
- Jurisdiction, safety standard and edition, study boundary, and included tasks.
- Field-verification date, drawing revisions, source documents, and unresolved data gaps.
- Every operating scenario, including charger and parallel-string states.
- Calculation method, evidence base, voltage and current range of applicability, and any enclosure or geometry limitations.
- Assumptions for source current, impedance, electrode gap, working distance, and clearing time.
- Results at the stated working distances, with units and conditions attached to each value.
- Labels, approach boundaries, PPE or other mitigation recommendations that are within the agreed scope.
Do not accept a result that presents a single number without the scenario and working distance that produced it. If the method is empirical or based on tests, the report should explain how the installation compares with the tested voltage, current, gap, electrode orientation, enclosure, and duration.
Understand the limits of common standards and models
IEEE 1584-2018
IEEE 1584-2018 covers three-phase AC systems from 208 V through 15 kV. It explicitly excludes DC calculations and PPE recommendations. Its equations, tables, and software implementations should not be presented as a universal DC solution.
IEEE 1584.2-2025
IEEE 1584.2-2025 is a data-collection guide for three-phase 50/60 Hz AC systems at or below 1000 V. Its checklist can illustrate the discipline of collecting complete field data, but it is not a DC checklist or a DC incident-energy method.
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NFPA guidance and draft material
NFPA committee material associated with the 2026 first-draft report emphasizes source short-circuit information, circuit impedances, and DC modeling. Because it is a draft revision document, verify the final edition and the rules adopted by the authority having jurisdiction before treating any wording as enforceable.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why a single DC formula cannot be assumed
DC arc behavior changes with voltage, available current, electrode geometry and gap, enclosure, and arc duration. Older maximum-power approaches can be conservative for some systems, while test results vary substantially with the setup. The analyst should state the method and its evidence instead of selecting a formula solely because it is familiar.
Published test programs illustrate the spread, but their counts are not universal hazard limits:
| Study | Test conditions reported | How to use the evidence |
|---|---|---|
| Cantor, Gordon, and Marri (2024): 22 tests | 192, 240, and 480 V; 5 kA and 20 kA available current; closed-parallel electrodes; open-air and enclosed setups; calorimeters at 18 inches, with an additional 6-inch calorimeter for some tests | Shows why voltage, current, enclosure, and distance must accompany a result |
| Gray, Robert, and Gauthier (2020): 23 tests | 105–500 V; 7–20 kA available current; inline electrodes; enclosed and open-air setups; 3 mm, 6 mm, or 25 mm initial gaps | Demonstrates that electrode gap and configuration are material inputs |
| Hildreth and Feeney (2018): 58 tests | 125 V, 1300 Ah station battery; approximately 3.9 kA and 7.85 kA available current; varied gaps, charger contribution, inductance, tools, and panelboard conditions | The authors reported industry-standard models overestimated incident energy by more than tenfold for this studied setup; that finding must not be generalized to other systems |
These studies support a request for method transparency, not a universal pass/fail threshold. An engineer should explain whether the selected approach has been validated for the installation’s voltage, current, geometry, enclosure, and duration.
Field-ready collection checklist
- Mark the equipment boundary and list every task and access point to be studied.
- Obtain the latest DC one-line and verify it in the field, including alternate and maintenance configurations.
- Compile source nameplates, battery manufacturer short-circuit data, charger limits, string arrangements, and other source contributions.
- Measure or document cable and bus lengths, conductor sizes, materials, connections, and significant impedances.
- Photograph and record every fuse, breaker, contactor, and controller; capture ratings, settings, and maintenance status.
- Request manufacturer time-current or total-clearing information for the calculated current range.
- Measure enclosure dimensions, electrode gap and orientation where applicable, door state, barriers, and worker working distance.
- Give the engineer the jurisdiction, safety-standard edition, field-data date, requested deliverables, and known uncertainties.
- Review the report for scenario-specific results, method applicability, assumptions, limitations, and labeling or mitigation actions.
Common data gaps and corrective actions
Only nominal voltage is available
Nominal voltage does not establish available fault current or arc duration. Obtain manufacturer short-circuit data and model the source-to-arc impedance.
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The breaker catalog number is missing
Photograph the nameplate and trip unit, record settings, and identify the upstream and downstream series arrangement. A generic breaker curve is not a substitute for installed-device data.
The drawing shows normal operation only
Interview operations and maintenance personnel about parallel strings, chargers, bypasses, and tie positions. Add each credible state to the scenario list for engineering review.
The task occurs inside a cabinet but only open-air data was supplied
Tell the engineer the actual enclosure and door condition. Ask whether the chosen method covers that geometry and how the limitation affects hazard evaluation.
The report uses an unexplained clearing-time assumption
Request the source curve, current at operation, and rationale for the time. If no manufacturer data exists, require the assumption and sensitivity or conservative treatment to be documented.
Bottom line: give the engineer a verifiable system, not just a voltage
A defensible DC arc-flash study starts with a field-checked one-line, complete source and impedance data, actual protective-device settings and clearing behavior, and task-specific geometry and working distance. The facility’s job is to gather and verify records; the qualified analyst’s job is to calculate available current at the arc, choose a method suited to the DC installation, and disclose its assumptions and limits. Because IEEE 1584-2018 and IEEE 1584.2-2025 address AC systems, insist that any DC result identify its own method and evidence rather than borrowing an AC calculation by default.
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