Protective device coordination and arc flash analysis are closely connected, yet they are often treated as separate parts of a power system study. In reality, the settings that improve system reliability can also have a significant impact on worker safety and arc flash hazard levels.
At the center of the relationship is clearing time. When an arc flash occurs, the protective device upstream must detect the fault and interrupt current flow. The longer the arc exists, the more thermal energy is released. Because of this, even relatively small delays in breaker operation can lead to large increases in incident energy.
This creates a challenge for engineers because coordination and arc flash reduction do not always support the same goal.
Protective device coordination is designed around reliability. In a properly coordinated system, the device closest to a fault trip first while upstream equipment remains energized. This minimizes outages and keeps the rest of the facility operating normally. To accomplish this, upstream breakers are often intentionally delayed so downstream devices have time to operate first.
That delay improves selectivity, but it can also increase arc flash energy.
A common example is a main breaker feeding several distribution panels. To maintain coordination, the breaker may use a short-time delay setting. During an arcing fault on the main bus, that intentional delay allows the arc to persist longer before the breaker trips. The result can be a dramatic increase in incident energy at the equipment.
In many facilities, the highest arc flash values are not caused by extremely high fault current alone. They are caused by protective devices operating too slowly during certain fault conditions.
This is why arc flash studies and coordination studies should never be performed independently. A small setting adjustment can completely change the incident energy results for a piece of equipment. Likewise, reducing arc flash energy by speeding up breaker operation may unintentionally sacrifice selective coordination and increase the likelihood of larger outages.
Engineers are often balancing two competing priorities: maintaining system reliability and improving worker safety. Faster tripping generally lowers incident energy, but excessive sensitivity can cause nuisance trips or unnecessary shutdowns. Slower tripping improves selectivity but may expose workers to higher thermal energy during a fault.
Modern protection schemes attempt to reduce this tradeoff. Technologies such as zone selective interlocking (ZSI) and maintenance mode settings allow systems to operate with normal coordinated delays during everyday operation while enabling much faster clearing when personnel are working on energized equipment. Under normal conditions, a breaker may use delayed settings to preserve coordination. When maintenance work begins, the breaker can temporarily switch to a faster instantaneous response. This reduces clearing time and lowers arc flash energy exposure for workers without permanently changing the system coordination strategy.
As electrical systems become more complex, the relationship between coordination and arc flash becomes even more important. Data centers, industrial plants, and facilities with multiple utility sources or large motor contributions often require careful balancing between uptime and safety performance.
Ultimately, protective device coordination is not just about keeping the lights on. It directly affects the severity of arc flash hazards throughout a power system. The most effective electrical safety strategies recognize that reliability and safety are interconnected engineering objectives, not separate studies performed in isolation.
It can. Improving coordination often involves adding intentional delays to upstream protective devices so downstream equipment has time to clear faults first. While this improves system reliability and selectivity, the additional clearing time can allow an arc flash to persist longer, increasing incident energy at certain locations within the electrical system.
Incident energy is directly related to the amount of time an arc flash is allowed to exist. The longer a breaker or protective device takes to detect and clear a fault, the more thermal energy is released. Even small increases in clearing time can result in significantly higher incident energy levels and greater arc flash hazards for workers.
In many cases, yes. Modern protection technologies such as zone selective interlocking (ZSI) and maintenance mode settings can help reduce clearing times during maintenance activities while maintaining selective coordination during normal operation. These approaches allow facilities to balance worker safety and system reliability rather than treating them as competing objectives.
Understanding the relationship between coordination and arc flash energy is essential for making informed decisions about both safety and system performance. If you're evaluating protective device settings, updating an arc flash study, or looking to improve electrical system reliability, our team can help identify the right balance for your facility.
About the Author
Kaitlin is an Electrical Designer with Hallam-ICS's Arc Flash and Electrical Safety team. Since joining Hallam-ICS in 2022 after earning her Bachelor's degree in Electrical Engineering from UNC Charlotte, she has supported clients with arc flash studies, electrical safety assessments, and power system analysis. Kaitlin enjoys collaborating with clients and colleagues to improve electrical system safety and reliability.
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About Hallam-ICS
Hallam-ICS is an engineering and automation company that designs MEP systems for facilities and plants, engineers control and automation solutions, and ensures safety and regulatory compliance through arc flash studies, commissioning, and validation. Our offices are located in Massachusetts, Connecticut, New York, Vermont, North Carolina and Texas and our projects take us world-wide.