A short-circuit level study (also called a fault level study) is an engineering analysis that calculates the prospective short-circuit current at key points in an electrical system. The results are used to confirm that switchgear, cables, and protective devices can safely withstand and interrupt faults, and that protection coordination will work as intended.
For EV charging sites, a short-circuit level study is often required when installing high numbers of chargers, adding new distribution boards, or connecting to a new transformer or grid connection.
Why a Short-Circuit Level Study Matters in EV Charging Infrastructure
It directly affects safety, compliance, and reliability.
– Confirms breakers, fuses, and switchgear have adequate breaking capacity (Icu/Ics)
– Validates equipment short-circuit withstand ratings to prevent catastrophic failure
– Provides inputs for selectivity (discrimination) and protection coordination studies
– Supports correct disconnection times and earthing strategy validation (especially for earth faults)
– Reduces risk of downtime caused by incorrectly rated protection or nuisance tripping
– Often required for permitting, commissioning, and insurer or utility approval
What a Short-Circuit Level Study Typically Includes
A complete study usually covers:
– One-line diagram model of the site electrical network (source to final circuits)
– Utility supply data (transformer rating, % impedance, fault level at point of connection)
– Cables, busbars, and switchgear impedances (lengths, sizes, materials)
– Fault calculations at defined nodes (main incomer, LV panels, subpanels, charger feeders)
– Different fault types: 3-phase, phase-to-phase, phase-to-neutral, phase-to-earth
– Worst-case assumptions (network strength, transformer tap position, parallel feeds)
– Results tables and compliance checks versus equipment ratings
Some studies also include arc flash risk evaluation, depending on site requirements and local standards.
How the Study Is Used for EV Charging Design
Short-circuit results influence multiple design decisions.
– Selecting breaker kA ratings for each distribution level
– Confirming charger feeder protection and fault loop performance
– Optimizing circuit segmentation so a fault affects only one charger or small group
– Choosing between fuses vs MCCBs/MCBs based on selectivity needs
– Determining whether additional sub-distribution boards are needed to manage fault levels
– Providing baseline data for a full protection coordination study
Typical Deliverables
– Updated one-line diagram with node names and ratings
– Fault level results (kA and/or MVA) at each node
– Device rating checks (switchgear, breakers, busbars, cable thermal withstand)
– Assumptions list and input data summary
– Recommendations (device upgrades, feeder changes, segmentation improvements)
Key Benefits of Doing the Study Early
– Prevents costly rework (wrong breaker ratings, underspecified panels)
– Improves uptime through better protection design and selectivity
– Speeds up approval and commissioning by providing required documentation
– Enables scalable expansion planning with known fault level margins
– Improves safety by ensuring faults can be cleared predictably
Limitations to Consider
– Output accuracy depends on the quality of input data (actual cable routing, transformer impedance, earthing)
– Utility network conditions can change over time, affecting fault levels
– On-site generation (PV, batteries) can complicate fault contribution assumptions
– A short-circuit study alone does not guarantee selectivity—coordination analysis is still required
Related Glossary Terms
Fault level analysis
Short-circuit level
Short-circuit current
Prospective fault current
Breaking capacity (Icu/Ics)
Overcurrent protection device (OCPD)
Selectivity (discrimination)
Feeder circuit
Main LV panels
Protection coordination study