A critical engineering study determining the maximum available fault current at every point in your electrical system to ensure safety and NEC compliance
A critical engineering study determining the maximum available fault current at every point in your electrical system to ensure safety and NEC compliance.
Short circuit analysis is an engineering study used to calculate the maximum electrical current that would flow in a power system during a fault condition. It is the foundational step in designing safe electrical distribution networks.
Fault current occurs when electrical current bypasses the normal load and follows a path of negligible resistance, usually to ground or between phases. This study quantifies the “system potential”—the maximum energy the utility and internal sources can deliver to a specific point—ensuring your system can handle the surge without vaporization or explosion.
A “bolted fault” assumes a solid connection with zero impedance between conductors, resulting in the highest possible current magnitude. This worst-case scenario is used to size equipment ratings. In contrast, an “arcing fault” flows through the air gap between conductors; while the current is lower due to arc resistance, the resulting energy release (Arc Flash) is often more dangerous to personnel.
Fault current is not a clean sine wave immediately after a fault occurs.
Neglecting short circuit analysis is a primary cause of industrial electrical accidents. The study bridges the gap between theoretical design and real-world safety.
When fault current exceeds a device’s rating, the magnetic forces can physically blow switchgear doors open, shatter insulators, and melt busbars. A proper analysis ensures that switchgear, cables, and transformers are mechanically robust enough to withstand these forces until the protective device clears the fault.
Short circuit data is the primary input for Arc Flash Risk Assessments. You cannot calculate incident energy (calories/cm²) or determine the correct PPE categories without knowing the precise magnitude of the bolted fault current. Lower fault currents do not always mean safer conditions, as they may result in longer trip times, increasing total energy exposure.
Selective coordination ensures that only the breaker closest to the fault trips, keeping the rest of the facility powered. To achieve this, engineers must know the available fault current to set the time-current curves (TCC) of breakers and fuses correctly, preventing “nuisance tripping” that shuts down critical operations.
Operating without a valid short circuit study is a violation of major electrical codes and safety standards.
OSHA 1910.303(b) requires electrical equipment to be free from recognized hazards. NFPA 70E (Standard for Electrical Safety in the Workplace) explicitly requires the maintenance of a current single-line diagram and an up-to-date short circuit study to label equipment with Arc Flash warnings.
A reliable study relies on high-fidelity data input. “Garbage in, garbage out” applies strictly to power system modelling.
The process begins with an accurate One-Line Diagram (OLD). Engineers must gather data on feeder lengths, conductor sizes, and transformer nameplate details. Crucially, the “Utility Contribution” (available fault MVA) must be obtained directly from the power company to establish the baseline energy entering the facility.
Impedance ($Z$) restricts current flow. The ratio of Reactance ($X$) to Resistance ($R$) determines how long the DC offset lasts. A high X/R ratio (common near generators and large transformers) means the fault current will remain asymmetrical (peaking higher) for longer, putting more stress on breakers.
When a short circuit occurs, magnetic fields in running motors collapse, momentarily turning them into generators. They feed current back into the fault. Large induction and synchronous motors can significantly increase the total fault current, often pushing a borderline system over its safety rating.
Electrical systems are dynamic; a study performed ten years ago is likely obsolete today.
For any new construction, a short circuit study is required before energization. It validates that the specified gear (e.g., a 65kA rated panelboard) is suitable for the actual installed environment.
Adding a new chiller, replacing a main transformer with a lower impedance unit, or installing on-site solar/cogen generation changes the fault profile. Any significant load addition or topology change warrants a recalculation.
NFPA 70E recommends updating the electrical system analysis every 5 years. Even if your facility hasn’t changed, the utility company may have upgraded their substation, increasing the fault current available at your service entrance.
The output of the study is a comparison table that highlights pass/fail ratings for every device.
The engineer compares the calculated “Available Fault Current” against the equipment’s “Short Circuit Current Rating” (SCCR). If the available current is 45,000 Amps and the panel is rated for 22,000 Amps, the equipment is dangerously “over-dutied.”
Underrated devices are code violations and ticking time bombs. During a fault, an underrated breaker may weld shut, explode, or fail to interrupt the arc, leading to total destruction of the switchgear.
If equipment fails the study, mitigation is necessary. Solutions include:
A Short Circuit Analysis is not just a regulatory checkbox; it is the mathematical backbone of your facility’s electrical safety program. By accurately calculating fault currents and ensuring compliance with NEC and NFPA standards, you protect your infrastructure from catastrophic failure and your workforce from life-threatening hazards.
Ensure your facility is compliant, safe, and resilient.
Aura Safety Risk Consultant
Delivering comprehensive HSE management and engineering consultancy solutions to ensure safety, compliance, and sustainable industrial growth.
Contact Us Today:
Phone: +91 9999 402 106
Website: https://aurasafety.com/contact-us
+91 99994 02106
Identifies arc flash hazards and defines safe working limits
Evaluates electrical risks to prevent failures and accidents
Analyzes power quality issues caused by electrical harmonics
Classifies hazardous zones for safe electrical equipment use
Assesses lightning threats and protection system needs
Optimizes relay settings for selective fault protection
Electrical safety audits and engineering solutions minimizing risks, preventing accidents.
Detects overheating in electrical equipment using infrared
Short Circuit Analysis calculates the magnitude of the current (Amps) during a fault to check equipment ratings. Arc Flash Analysis uses that data to calculate the thermal energy (Calories) released to determine safe distances and PPE for workers. You cannot do an Arc Flash study without a Short Circuit study first.
The cost varies significantly based on facility size, the number of bus nodes, and data availability. Small commercial buildings may range from $2,000 to $5,000, while complex industrial plants can range from $15,000 to $50,000+.
Engineers use software like ETAP, SKM Power*Tools, or EasyPower to perform the complex calculations. However, the software requires expert human input for modeling scenarios, validating utility data, and interpreting NEC compliance correctly.
If no diagram exists, a field survey is required. Engineers must visit the site to trace conduits, open panels (safely), and record nameplate data to build the system model from scratch before the analysis can begin.
The Utility provides the "Infinite Bus," or actual fault data at the point of common coupling. If they upgrade their infrastructure (e.g., larger substation transformers), the fault current entering your building increases, potentially rendering your existing equipment unsafe
Yes, under strict NEC conditions. Series rating allows a downstream breaker to have a lower rating if the upstream breaker is tested and listed to protect it. This must be engineered carefully and cannot be used if motors contribute significant back-feed current between the two devices.
