Arc Flash Study Methodology: IEEE 1584, Labels and Mitigation

An arc flash is a release of energy so intense that it can vaporize copper, throw molten metal and cause severe burns at a distance of several feet. Whether a worker standing at a switchboard faces a manageable event or a life-threatening one depends on numbers that can be calculated long before anyone opens a door. That calculation is the arc flash study, and it is one of the most practical deliverables in the electrical engineering services a project can buy.

Budlong has engineered power systems since 1958, and our history includes hospitals, laboratories, airports and generating plants where electrical work cannot always wait for a shutdown. This article takes a methodology-first view: the inputs, the math at a conceptual level, the label, the mitigation toolbox and the project stages where timing decides cost. For a compliance overview, start with our earlier guide below.

Also Read: Arc Flash Analysis and NFPA 70E Compliance

1. What Is an Arc Flash Study?

The hazard in engineering terms

An arcing fault occurs when current jumps through air between conductors or from a conductor to ground, often because of a dropped tool, a failed insulator, contamination or a loose termination. The arc converts electrical energy into heat, light, pressure and sound. The engineering question is how much thermal energy reaches a worker at a defined distance, and for how long.

What the study delivers

The study produces a table of results for every piece of equipment that may be examined or serviced while energized. Each row contains a bolted fault current, an arcing current, an arcing time, an incident energy value, an arc flash boundary and a recommended PPE level. The study also supplies labels, a summary of locations that exceed a chosen threshold and a list of mitigation options.

How it differs from related studies

An arc flash study does not make equipment safe by itself. It tells you how dangerous each location is, so that you can decide whether to reduce the hazard, restrict the work or protect the worker.

2. How the Calculation Works

The IEEE 1584-2018 approach

The IEEE 1584 guide gives empirical models built on large-scale laboratory testing. The 2018 edition calculates arcing current first, then incident energy, then the arc flash boundary. It covers three-phase systems from low voltage up to 15 kV within stated ranges of fault current, gap and enclosure size, and it uses a set of electrode configurations to represent how conductors are arranged inside the equipment.

Inputs that matter

• Voltage and bolted fault current: taken from the short circuit model.
• Electrode configuration: vertical conductors in a box, vertical conductors terminated in an insulating barrier, horizontal conductors in a box, vertical or horizontal conductors in open air.
• Enclosure size: height, width and depth, with corrections for shallow enclosures.
• Gap between conductors: typical values are tied to equipment type and voltage class.
• Working distance: the distance from the likely arc source to the worker, which depends on the equipment and the task.
• Arcing time: the time the upstream protective device needs to clear, read from its curve at the arcing current.

Why arcing current is not bolted current

A real arc has resistance, so the arcing current is lower than the bolted fault current. This creates a counterintuitive effect. A lower arcing current can fall on a slower part of the protective device curve, so the clearing time grows, and the incident energy can end up higher than at the full fault level. The standard therefore requires an additional, reduced arcing current case, and the engineer applies whichever yields the larger energy.

From energy to boundary

The arc flash boundary is the distance at which a person without protection would receive an energy that can cause a second-degree burn, commonly represented by an incident energy of 1.2 calories per square centimeter. The study solves for that distance for each location, and the result appears on the label.

3. Calculation Methods and Label Approaches

Which calculation method fits which system

NFPA 70E Annex D lists several approaches. IEEE 1584 serves most three-phase AC systems in its voltage and current range. Other methods address DC systems, higher voltages and open-air arcs. The engineer documents the method used and the reason for choosing it, because 70E requires the basis for label data to be recorded.

Incident energy analysis versus PPE category tables

NFPA 70E allows two ways to select PPE. In the incident energy analysis method, the study calculates energy at each location and PPE is chosen to match. In the PPE category method, tables in the standard assign categories by equipment type, voltage, fault current and clearing time, within stated limits. A label should generally rely on one method for a given piece of equipment, not a mix. The comparison below shows how the choices play out.

PPE categories at a glance

Results above the top category have no corresponding PPE in the standard, which is why many owners treat any location near 40 calories per square centimeter as a trigger for engineering controls, not heavier clothing.

4. Regulatory and Standards Requirements

NFPA 70E

NFPA 70E, the Standard for Electrical Safety in the Workplace, is published by NFPA. Section 130.5 requires an arc flash risk assessment before work within the limited approach boundary, with the assessment reviewed at intervals not exceeding five years and updated after modifications. It defines the content of labels and the relationship between the study and the safety program.

NEC marking and labeling

NEC 110.16 requires warning labels on equipment such as switchboards, panelboards, industrial control panels and motor control centers that are likely to need examination, adjustment, servicing or maintenance while energized. Some editions add further marking for service equipment, so confirm the adopted edition on your project.

OSHA and state rules

The Occupational Safety and Health Administration does not adopt 70E by reference, but it enforces employer duties through its general industry electrical rules, personal protective equipment requirements and the general duty clause. California workplaces are also covered by the state occupational safety program and its electrical safety orders.

Label format and supporting standards

Label layouts commonly follow ANSI Z535 safety sign principles. IEEE 1584.1 gives a guide for specifying the scope and deliverables of a study, and it is useful when writing a request for proposal.

Also Read: Electrical Engineering for Safety, Reliability and Efficiency

5. Applications by Building Type

Hospitals and health facilities

Hospitals cannot shut down large parts of their power system easily, so more work occurs on energized equipment than in most buildings. The health facilities we design combine utility sources, generators and automatic transfer equipment, and every path needs its own set of results. Our reference project at Kaiser Permanente Baldwin Park shows the scale of generation that sits behind a medical campus.

Laboratories and industrial plants

Process equipment, large motors and variable frequency drives raise the number of devices requiring labels. Laboratories such as Amgen need power that keeps research running, so energized work is common. Our industrial and laboratory and industrial MEP practices incorporate arc flash planning from the one-line forward.

Data centers and mission critical sites

Concurrent maintainability means maintenance occurs on live distribution paths. Arc flash energy at paralleled sources and large UPS output boards needs careful handling, and the article on power distribution for data centers describes the architecture. See also our mission critical experience.

Offices, schools and institutional buildings

Lower service sizes mean lower energy at many locations, but main switchboards still require study, and tenant changes can alter results over time. The cost of a study is small relative to the cost of an injury or a shutdown.

Planning an arc flash study?

Talk with our electrical team about scope, data collection and mitigation options before equipment is ordered.

Request an arc flash consultation

6. Design Process, Labels and Project Timing

Data collection to final report

1. Gather the one-line diagram, utility data, transformer and generator nameplates, cable data and device settings.
2. Build or update the short circuit and coordination model.
3. Assign electrode configurations, enclosure sizes, gaps and working distances for each location.
4. Calculate incident energy at the full and reduced arcing current, and take the worse result.
5. Review locations above the owner’s threshold and test mitigation options in the model.
6. Issue the report, install labels and train the maintenance staff.

What a label contains

When each stage should happen

Early review matters because mitigation chosen late costs more. A maintenance mode feature added in design is a trip unit option, while the same feature added after installation can mean a breaker replacement. Our guide to early MEP coordination explains the broader benefit.

7. Special Cases and Difficult Conditions

DC systems, batteries and UPS

DC arcs do not self-extinguish at a current zero, and batteries have no upstream device to clear in some cases. These systems need DC methods, not IEEE 1584 AC equations, and the engineer should document the approach.

Generators and low fault current sources

When a generator carries the load, the fault current can be low and the clearing time long, so the energy can exceed the utility case. Studies for emergency systems should analyze both sources. The USC NTT generator replacement illustrates a retrofit where the new source changes the hazard picture.

Medium voltage equipment

Above 600 volts, gaps are larger and the energy depends heavily on relay settings. Relay-based protection, with its adjustable delay, often determines the result, so protection engineers and arc flash analysts should work together.

Small low-voltage systems

Systems fed from small transformers have sometimes been treated as low hazard, but any exclusion should be documented with the supporting analysis, not assumed.

Existing buildings

Older facilities often have missing drawings, discontinued breakers and unknown settings. A field survey is the starting point, and temporary assumptions need to be replaced as data improves.

8. Specifying the Study and Understanding Cost

What a good scope includes

• The standards and editions to be used, including IEEE 1584 and the version of NFPA 70E.
• The equipment boundaries, such as everything from the utility service to 120 volt panelboards, or only larger gear.
• The incident energy threshold that triggers mitigation review.
• Label size, material and mounting requirements.
• Delivery of the model files to the owner.
• Training for the maintenance team.

Who should do the work

The engineer of record, the equipment manufacturer and an independent firm can all produce a study. The engineer of record knows the design intent, while the manufacturer knows its trip units. Independent review helps when the owner wants a second opinion. Whichever route is used, require that the report states its assumptions in plain language.

Cost drivers

• Size: the number of locations to be labeled.
• Data quality: unknown settings and missing nameplates add survey time.
• Complexity: multiple sources, tie breakers and operating modes add cases.
• Mitigation work: design iterations to reduce incident energy.
• Labels: printing, durable materials and field installation.

Our article on estimating MEP engineering costs helps place the study in a broader budget, and the electrical load calculation guide covers the upstream data.

9. Best Practices, Mistakes and Maintenance

Mitigation options

Mitigation follows the hierarchy of risk controls: eliminate the hazard where possible, then use engineering controls, then warnings and procedures, then PPE. The table below compares common engineering controls.

Also Read: Why Data Center Power Systems Fail

Common mistakes

• Applying generic arcing times instead of reading them from actual device settings.
• Changing breaker settings in the field without updating the study.
• Using labels from an older study after a utility or transformer change.
• Reducing energy with instantaneous settings that destroy coordination for life safety circuits.
• Treating labels as the whole program, instead of training and procedures.

Testing, commissioning and maintenance

The study is only as good as the settings and the device condition behind it. Testing confirms that breakers trip within the times assumed, and maintenance keeps them within tolerance. Our building commissioning process and the guide to commissioning versus retro-commissioning describe how verification applies to new and existing facilities. Our commissioning services include protective setting checks. The US Department of Energy also publishes general resources on facility energy and electrical system performance.

10. Where Budlong Delivers This

Budlong works from offices in Glendale, downtown Los Angeles, Camarillo and Fremont, and serves Los Angeles, Ventura, Orange, San Bernardino, Riverside and Santa Barbara counties. Our MEP engineering and electrical solutions teams carry arc flash analysis from design through energization.

11. Related Reading

12. Frequently Asked Questions