What an arc flash is
An arc flash is a sudden release of energy when current jumps through the air between conductors, or from a conductor to ground. It can start when a tool slips inside a live panel, when a worn connection fails, when dust or moisture tracks across insulation, or when an old breaker fails while it is being operated.
The arc can be far hotter than the surface of the sun. It vaporizes copper, throws molten metal and creates a pressure wave, blinding light and a loud blast. People in front of the equipment can suffer severe burns, hearing damage and injuries from debris. An event in main switchgear can also shut a building down for days or weeks while parts are found.
Why it matters to owners
Arc flash is not only the electrician's problem. Alberta's occupational health and safety legislation requires employers to assess hazards and protect workers. In Canada, CSA Z462 (Workplace electrical safety) is the standard most organizations use to manage electrical hazards, including arc flash.
In practice, owners control the things that decide how dangerous their equipment is: whether it is maintained, whether a study has been done, and whether the information is posted and current. When a contractor arrives to work on your switchgear, they will ask for arc flash labels and an up-to-date single-line diagram. Without them, they have to assume the worst and plan around it, which costs time and money.
Facility staff should never open energized panels or switchgear, even for a quick look. Opening covers on live equipment is work that requires a qualified electrician, a hazard assessment and the right PPE.
The arc flash study and the label
An arc flash study, also called an incident energy analysis, models your electrical system to estimate how much energy an arc would release at each piece of equipment. It is normally done by or under a professional engineer, often together with a short-circuit study and a protective device coordination study.
The study needs real data: the fault current available from the utility, transformer sizes and impedances, cable sizes and lengths, and the settings of every breaker and fuse. Collecting this data is often the longest part of the job, and an accurate single-line diagram makes it much faster.
The results go on labels fixed to each piece of equipment.
What changes the hazard
Incident energy depends mostly on two things: how much fault current is available, and how fast the upstream protective device clears the fault. A slow-clearing breaker can produce a higher hazard even where fault current is lower. That is why study results sometimes surprise people, and why changes to the system matter. The hazard can change when:
- The utility replaces or upsizes the transformer feeding your building
- You upgrade the service or add large equipment
- Breaker trip settings are changed
- Equipment is replaced or reconfigured
- A generator or a solar system is added
There are good ways to reduce the hazard. The best is to de-energize equipment before working on it. Others include energy-reducing maintenance switches on large breakers, adjusted trip settings, current-limiting fuses, remote racking and operating, infrared windows for scanning, and arc-resistant switchgear when equipment is replaced.
Keep the study current and the gear maintained
A study is a snapshot. CSA Z462 calls for the assessment to be reviewed when the system is modified and at regular intervals, which recent editions set at no more than five years. Check the study date on your labels. If it is old, or if there are no labels, start there.
Maintenance matters just as much. The study assumes each breaker trips as designed. A breaker that has not been exercised or tested in years may trip slowly or not at all, and the real hazard can be much higher than the label says. See our guide to preventive maintenance programs.
A short checklist for owners
- Find out whether an arc flash study exists, and its date.
- Walk the electrical rooms and check that labels are present and readable.
- Make sure your single-line diagram matches what is installed.
- Put breaker exercise and testing into your maintenance plan.
- Require contractors to follow CSA Z462 and your own safe work rules.
- When equipment is replaced, ask how the new design reduces the hazard.
Common questions
Is an arc flash study required?
Employers must assess electrical hazards, and an incident energy analysis is the most common way to do that for larger equipment under CSA Z462. Your safety advisor or insurer may have specific expectations. If workers ever operate or service your equipment, you need the information a study provides.
Who does the study?
It is normally done by or under a professional engineer. An electrical contractor often helps gather field data, such as equipment nameplates, cable lengths and breaker settings.
Does a high number on the label mean the equipment is unsafe?
It means the consequences of an arc would be severe, so work on that equipment needs more planning, more PPE, or de-energizing. There are often ways to lower the number, such as a maintenance switch or new settings.
Do labels expire?
The label itself does not, but the information can go out of date when the system or the utility supply changes. Review it when the system changes and on the interval the standard sets.
Codes and permit rules change and every building is different. For work on your system, talk to a licensed electrician and your local permit authority.