Arc Flash Guide: Where to Start

An arc flash is the release of heat, light and pressure when current flows through the air between conductors or to ground. This arc flash guide is for facility and safety managers, electricians and engineers who need to understand the hazard, what an arc flash study involves, and what the labels and PPE rules mean.

The articles below are the ones we would give a new colleague, in the order we would give them. Each section also links the calculator or interactive explainer that fits, and the service page for that part of the work if you would rather talk to an engineer.

1. Start with the basics

• What happens during an arc flash: Start here. It covers the causes, what an arc does to people and equipment, and how a walkdown and the studies behind a label help prevent one.
• The main causes of arc flash: Human error, dust and debris, and equipment failure, with ways to prevent each.
• The dangers of arc flash: The injuries an arc flash can cause and why an assessment comes before energized work.
• Ground fault vs. short circuit: The two fault types, how they differ and which devices protect against each.

To see how these studies fit with our other work, visit the electrical power engineering page, which also covers design, load studies and grounding tests.

2. How the hazard is assessed

• The steps of an arc flash analysis: Gathering one-line diagrams, field verification, modeling and labeling, with the OSHA and NFPA 70E^® requirements behind them.
• Why short circuit analysis comes first: A study starts from the available fault current. This explains what a short circuit analysis checks and how it sets up the coordination and arc flash studies.
• The purpose of a coordination study: What engineers check in a protective device coordination study and how correct settings limit outages and equipment damage.
• What an arc flash study report should include: Methodology, equipment ratings, worst-case incident energy and labels, so you can check a report before you accept it.
• Walk through a sample arc flash study (interactive): Select a bus to see its label, the inputs behind it and the device that clears the arc.
• See what fault current does to selectivity (interactive): Set a fault current on a time-current chart and see the trip times and where upstream and downstream devices overlap.
• Build a data request for a power study: A printable checklist of the system data an arc flash, short circuit or coordination study needs.

The matching services are arc flash studies, short circuit analysis and protection and coordination.

3. Standards and rules

• Arc flash protection and OSHA: How OSHA regulations and NFPA 70E apply to employers, and where NFPA, IEEE and the National Electrical Safety Code^® fit.
• NEC 240.87 arc energy reduction: The requirement for large circuit breakers, the methods that satisfy it and how to document them.
• NFPA codes and standards: Where NFPA 70^® (the National Electrical Code^®) and NFPA 70E sit among the other NFPA codes.

We teach these rules in our electrical safety training, which covers NFPA 70E and IEEE 1584-2018.

4. Labels and PPE

• Arc flash labeling: What a label must show, where its values come from, and when you need an incident energy analysis instead of the PPE category tables.
• Arc flash PPE categories explained: How a PPE category is chosen and the minimum arc rating for each category in NFPA 70E.

5. Common problems and how to reduce the hazard

• Ways to reduce arc flash incidents: An electrically safe work condition, lower fault current, training, PPE, maintenance, arc-resistant equipment and labels.
• Arc flash mitigation techniques: De-energizing, remote operation, ARMS and hazard analysis, and what each one changes.
• Preventing arc flash fires: Risk assessments, preventive maintenance, lockout/tagout, training and arc-rated PPE.
• Keeping a study current: Why an arc flash study is not a one-time job, and when to schedule an update.
• After an arc flash: failure analysis: What an arc flash leaves behind and how a forensic failure analysis finds the cause.

6. Calculators and tools

• Arc flash calculator (IEEE 1584-2018): Estimates the incident energy and the arc flash boundary at one piece of equipment. It is a screening tool: it does not choose PPE or make a label.
• Available fault current calculator: A point-to-point estimate of the fault current at a transformer and the equipment it feeds, the first input to any arc flash estimate.
• Per-unit calculator: Works a three-phase fault current problem in per-unit, step by step.
• All engineering calculators: Our free calculators and interactive explainers in one place.

How Dreiym Engineering Can Help

We perform arc flash studies together with the short circuit analysis and protective device coordination studies they rely on, modeled in ETAP^® and SKM. Our electrical power studies are led by Brian J. Brackensick, M.S., P.E., with field data collection by Ruben A. Rodriguez. We print and install arc flash labels or ship them to you, and we offer training on IEEE 1584-2018 and NFPA 70E. Our engineers are licensed Professional Engineers with active and past licensure in multiple states, and reports are PE-stamped where required. Contact us or call (866) 621-6920 for a free quote. We typically respond within one business day.