Short Circuit and Coordination Study

A short circuit and coordination study is an engineering analysis of your facility’s electrical distribution system that determines the available fault current at each point in the system and verifies that protective devices (circuit breakers, fuses, and relays) are properly rated and coordinated to clear faults safely. This study is a foundational requirement for electrical system safety, NEC compliance, and arc flash hazard analysis.

Arc Flash Florida provides short circuit analysis and protective device coordination studies for commercial and industrial facilities throughout the state of Florida.

What Is a Short Circuit Study?

A short circuit study calculates the maximum fault current (also called available fault current or short circuit current) that can flow at each point in your electrical distribution system during a fault condition. This fault current is determined by the utility source capacity, transformer impedances, conductor sizes and lengths, and the configuration of your electrical equipment.

NEC Section 110.9 requires that all overcurrent protective devices (circuit breakers and fuses) have an interrupting rating sufficient to handle the available fault current at their installed location. NEC Section 110.10 further requires that protective devices, their mounting, and the conductors they protect be selected and coordinated so that the circuit protective devices clear a fault without extensive damage to the electrical equipment. A short circuit study provides the calculations necessary to verify that your system meets both of these requirements.

What Is a Coordination Study?

A coordination study (also called a selective coordination study) evaluates the time-current characteristics of all protective devices in your electrical system to ensure they operate in the correct sequence during a fault. Proper coordination means that the protective device closest to the fault trips first, isolating only the affected circuit while the rest of the system continues to operate.

Without proper coordination, a fault on a branch circuit can trip an upstream breaker or blow a main fuse, causing a widespread outage that affects equipment and operations far beyond the fault location. In critical facilities such as hospitals, data centers, and manufacturing plants, this kind of cascading outage can create safety hazards and significant financial losses.

IEEE 551 (IEEE Recommended Practice for Calculating Short-Circuit Currents in Industrial and Commercial Power Systems, also known as the Violet Book) provides the industry-standard methodology for performing these calculations.

What the Study Includes

Short Circuit Analysis

The short circuit analysis portion of the study determines the maximum available fault current at each bus, panel, switchboard, motor control center, and other equipment locations in your electrical system. Calculations are performed for both three-phase and line-to-ground fault conditions. The results are compared against the interrupting ratings and withstand ratings of all protective devices and equipment to identify any locations where devices are underrated for the available fault current.

Protective Device Coordination

The coordination portion evaluates the time-current characteristics (TCC) of all series-connected protective devices from the utility source through the distribution system. Using coordination software, the study plots the operating curves of each device to verify that upstream and downstream devices coordinate properly. Where coordination gaps exist, the study provides recommended settings adjustments or device replacements to achieve selective coordination.

System Modeling

A detailed electrical model of your system is created using your one-line diagrams, equipment nameplate data, conductor specifications, and utility fault current information. This model serves as the basis for both the short circuit and coordination calculations and can be updated as your system changes over time.

Deliverables

The completed study includes a written report documenting all fault current calculations at each point in the system, time-current coordination curves showing device coordination (or lack thereof), identification of any underrated equipment or protective devices, recommended device settings and replacements where needed, and updated one-line diagrams reflecting the as-found system configuration.

Connection to Arc Flash Hazard Analysis

A short circuit and coordination study is a prerequisite for a complete arc flash hazard analysis. The fault current values calculated in the short circuit study are direct inputs to the incident energy calculations performed during an arc flash study per IEEE 1584-2018. The protective device settings verified and optimized during the coordination study directly affect the arc flash incident energy at each equipment location, because faster-clearing devices reduce the duration of an arcing fault and therefore reduce the incident energy exposure to personnel.

In many cases, optimizing protective device settings through a coordination study can significantly reduce the PPE requirements at specific equipment locations by lowering the calculated incident energy. This means a well-executed coordination study not only improves system reliability but can also reduce the arc-rated PPE burden on your employees.

Arc Flash Florida performs short circuit and coordination studies alongside arc flash hazard analysis to provide a complete picture of your electrical system’s safety profile.

When Is a Short Circuit Study Required?

A short circuit and coordination study should be performed or updated when:

• New construction or major renovation: Any new electrical installation or significant modification to the distribution system requires verification that protective devices are properly rated and coordinated for the new configuration.
• Utility changes: If your electric utility has increased the available fault current at your service entrance (due to utility system upgrades or new substations), existing protective devices may no longer have adequate interrupting ratings.
• Equipment additions: Adding large motors, generators, or other significant loads changes the fault current contribution and may affect coordination throughout the system.
• Arc flash study requirements: A current short circuit study is required as the basis for an arc flash hazard analysis per NFPA 70E 2024 and IEEE 1584-2018.
• Insurance or authority having jurisdiction (AHJ) requirements: Many insurance carriers and local inspectors require current short circuit and coordination studies as a condition of coverage or occupancy.
• Age of existing study: Industry best practice recommends reviewing and updating short circuit studies every five years or whenever significant system changes occur.

Data Required for the Study

To perform a short circuit and coordination study, the following information is typically needed:

• One-line diagrams: Current single-line diagrams of the electrical distribution system from the utility service entrance through all distribution levels.
• Utility fault current data: The available short circuit current at the service entrance, provided by your electric utility.
• Transformer data: Nameplate information including kVA rating, impedance, voltage ratings, and tap settings for all transformers.
• Protective device data: Manufacturer, model, frame size, ampere rating, and current trip unit settings for all circuit breakers. Manufacturer, type, voltage rating, and ampere rating for all fuses.
• Conductor data: Cable type, size, material (copper or aluminum), number of conductors per phase, conduit type (steel or PVC), and run lengths for all feeders and significant branch circuits.
• Motor data: Horsepower, voltage, and nameplate data for motors that contribute to fault current (typically 50 HP and above).
• Generator data: If on-site generation is present, nameplate data including subtransient reactance values.

Statewide Service Across Florida

Arc Flash Florida provides short circuit and coordination studies for commercial and industrial facilities throughout the state. Our team serves operations in Tampa, Orlando, Jacksonville, Miami, Fort Lauderdale, St. Petersburg, Lakeland, Sarasota, Tallahassee, and communities statewide. Contact Arc Flash Florida to discuss the scope and requirements for your facility’s study.