Short Circuit and Fault Current Studies
A short circuit study establishes the available fault current at every bus in your facility and checks it against the interrupting and withstand ratings of the equipment actually installed there. It is the foundation both coordination and arc flash work is built on.
It is also the study most likely to surface an unwelcome finding: equipment that was adequately rated when installed and is no longer adequately rated today, because the utility has since strengthened the supply.
What the study establishes, and the code basis
Available symmetrical and asymmetrical fault current at each bus, including motor contribution.
Comparison against nameplate interrupting ratings for breakers and fuses, and withstand ratings for switchgear, panelboards, busway and cable.
Identification of under-rated equipment, with options: replacement, current-limiting protection upstream, or a documented series rating where one is recognized.
Utility source data confirmed against the supplying utility rather than assumed.
Code basis
The Canadian Electrical Code requires that equipment be capable of interrupting or withstanding the fault current available at its point of installation. Demonstrating that requires a calculation, not an estimate — and inspectors increasingly ask to see it, particularly on service upgrades and on additions to older distribution.
When to run one
Before a service upgrade, so that the new available fault current is known before equipment is ordered.
When adding generation, including standby generators and inverter-based sources, which change fault contribution.
When the utility notifies you of a transformer or feeder change.
As the first step of any arc flash study, because incident energy cannot be calculated without it.
Deliverables
A sealed report giving available symmetrical and asymmetrical fault current at every modelled bus, with the source impedances and assumptions stated in full.
An equipment adequacy schedule comparing calculated fault duty against the interrupting and withstand rating of each device, with any under-rated equipment called out explicitly.
Updated single-line diagrams reflecting as-found conditions, annotated with fault levels.
The ETAP or EasyPower model file, so a future service upgrade or transformer change can be re-run rather than re-created.
Where equipment is found under-rated, a prioritized set of options: series rating where it is defensible, current-limiting devices, impedance changes, or replacement.
Common questions
Why does the utility number differ from the study number? The utility gives you an available fault current at the point of supply, usually a conservative maximum. The study carries that through your transformers, cable lengths and motor contribution to give a bus-by-bus result. Sizing everything to the utility number over-specifies equipment; ignoring it under-specifies the service entrance.
Do motors matter? Yes. Induction motors feed the fault for the first few cycles, and on a motor-heavy plant that contribution is the difference between a device that is adequately rated and one that is not. We model motor contribution rather than assuming it away.
How long does it take? As a rule we mobilize to site within about two weeks of award and issue the sealed report about four weeks after the field visit. Larger services with many distribution points run longer, and we will tell you that before you commit rather than after.
The utility just told me they are upgrading my feed. Does that change anything? It can change everything. A utility-side transformer or conductor change raises available fault current at your service, and equipment that was adequate can stop being adequate without anything inside your fence changing.