Short-Circuit and Coordination Studies: Why Every Industrial Facility Needs One

Most facility managers know their plant has circuit breakers, fuses, and relays protecting the electrical system. Far fewer can say with confidence whether those devices are actually set correctly for the fault current their system can produce, or whether a fault at one panel will trip only that panel instead of shutting down half the plant.

That is what a short-circuit and coordination study answers. It is one of the most consequential pieces of electrical engineering a facility can commission, and one of the most commonly skipped, especially in older plants where equipment has been added, moved, or upgraded piecemeal over the years without anyone recalculating what the system can actually deliver during a fault.

What a Short-Circuit Study Actually Calculates

A short-circuit study starts with a single-line diagram of the facility's electrical distribution system, from the utility service entrance down through transformers, switchgear, panels, and motor control centers. Using that diagram along with equipment nameplate data, cable lengths, and utility fault contribution figures, an engineer calculates the maximum available fault current at every point in the system.

This is not a guess or a rule of thumb. It is a modeled calculation of how much current would flow if a bolted fault occurred at each bus, panel, or piece of equipment. That number matters because every breaker, fuse, switchgear bus, and piece of equipment has an interrupting rating or short-circuit current rating (SCCR), and if the available fault current at that location exceeds what the equipment is rated to safely interrupt or withstand, the equipment can fail catastrophically during a fault instead of clearing it safely.

NEC Section 110.24 requires service equipment in non-dwelling occupancies to be field marked with the maximum available fault current and the date that value was calculated, and that marking has to be updated any time system changes affect it. There is an exception for industrial installations where qualified persons maintain and supervise the equipment, but even where the label itself is not mandatory, the underlying calculation is still what protects switchgear and other equipment rated for a specific fault current, along with the people working on it.

Why the Coordination Study Matters Just as Much

The short-circuit numbers feed directly into the second half of the study: coordination. A coordination study looks at every protective device in the system, from the utility-side main down to the smallest branch breaker, and plots their trip characteristics on time-current curves to determine whether they will operate in the right sequence during a fault.

The goal is straightforward: when a fault happens on a branch circuit or at a single motor control center bucket, only the nearest upstream device should trip. Everything else on the system should stay energized and unaffected. Without a proper coordination study, it is common to find that an upstream breaker trips at the same time as, or even before, the downstream device closest to the fault, which means a single fault at one machine can shut down an entire production line or an entire building.

This is closely related to but distinct from selective coordination, which is a specific NEC requirement that applies to emergency systems, legally required standby systems, and certain healthcare and elevator circuits. A full coordination study covers the entire facility, not just the systems where selective coordination is legally mandated, because unplanned plant-wide outages are expensive regardless of whether the code technically requires coordination on that particular circuit.

How This Connects to Arc Flash and Worker Safety

Short-circuit and coordination data is not just about keeping the lights on. It is the foundation that arc flash hazard calculations are built on. Arc flash studies, typically performed using the IEEE 1584 methodology referenced by NFPA 70E, use the available fault current at each piece of equipment along with the clearing time of the protective device upstream to calculate incident energy, the arc flash boundary, and the required PPE category for anyone working on that equipment.

A device that clears a fault faster produces a lower incident energy value. This is part of why coordination and arc energy reduction are connected in the code itself. NEC Section 240.87 requires facilities to provide a documented method of reducing clearing time, such as zone-selective interlocking, differential relaying, an energy-reducing maintenance switch, or an appropriately set instantaneous trip, on any circuit breaker whose trip setting is rated or adjustable to 1200 amps or higher. That requirement exists because slower clearing times on large breakers translate directly into higher arc flash incident energy for anyone working nearby.

NFPA 70E also calls for arc flash risk assessments to be reviewed at least every five years, or sooner if the electrical distribution system has changed in a way that could affect the fault current or clearing times the original study relied on. A facility that has added equipment, reconfigured switchgear, or upgraded its service since its last study is a strong candidate for an updated short-circuit and coordination analysis before those old arc flash labels can still be trusted.

When a Facility Should Have This Study Done

A few situations make a short-circuit and coordination study worth prioritizing, and it is also a natural step to pair with electrical commissioning whenever new equipment or a service upgrade is going into service:

• The facility has never had one done, or the most recent study predates significant equipment additions, service upgrades, or panel changes
• New machinery, motor control centers, or production lines have been added since the last study
• The utility has changed transformer sizing or service capacity, which changes the available fault current at the service entrance
• Breakers or fuses are being replaced and the facility wants to confirm the new devices are correctly rated and coordinated with existing equipment
• Arc flash labels on switchgear and panels are more than five years old or reference equipment that has since changed

How HRE Can Help

HRE Construction performs short-circuit and coordination studies as part of comprehensive electrical engineering support for industrial facilities across our service area. Our team builds or updates the facility single-line diagram, models available fault current at every bus and panel, and develops time-current coordination curves for every protective device in the system. Where gaps or misconfigured settings turn up, we recommend the specific corrections needed, whether that is a breaker setting change, a coordination curve adjustment, or an arc energy reduction method to satisfy NEC 240.87. The result is a documented study your team, your insurer, and your inspector can all rely on.

Ready to find out where your system stands? Contact HRE Construction to schedule a short-circuit and coordination study for your facility.

Frequently Asked Questions

How long does a short-circuit and coordination study take?

Timelines vary with facility size and how much existing documentation is available. A facility with an accurate, up-to-date single-line diagram and equipment nameplate data on hand moves faster than one where that information has to be verified in the field first.

Is a coordination study the same thing as an arc flash study?

No, but they are closely connected. The short-circuit and coordination study calculates fault current and protective device timing across the system. That data then feeds into the arc flash study, which calculates incident energy and PPE requirements at each piece of equipment.

Do I need this study if my facility is not adding equipment?

Yes, particularly if it has been several years since the last one or if the last study predates changes to the utility service or distribution equipment. Fault current and coordination settings can drift out of date even without visible plant changes, since utility-side transformer changes alone can shift the available fault current at your service.

What happens if the study finds a coordination problem?

The study will identify which devices are miscoordinated and recommend corrective settings, whether that means adjusting time-current curves, resizing a protective device, or adding an arc energy reduction method for breakers rated 1200 amps or higher under NEC 240.87.