Short Circuit Studies
No matter the size of your facility, completing a short circuit study – the evaluation of an electrical distribution system to determine the magnitude of current flow during an electrical fault condition at several points throughout the system – is a crucial component of project safety and success. Short circuits are the unintended flow of current on a low-resistance path that can introduce large amounts of destructive energy in the forms of heat and magnetic forces. Not only can these forces destroy distribution equipment, they also have life-threatening consequences for personnel working on the equipment.
Short circuit studies are performed to ensure the electrical distribution system meets the requirements of the National Electric Code (NEC), which requires overcurrent protection devices to have an interrupt rating and electrical equipment to have a short circuit rating not less than the maximum available fault current. The values calculated at different points throughout the system are used in setting these ratings. Further, this information is used in performing an arc-flash study, which sets the criteria for the personal protective equipment utilized by personnel while working on the equipment.
Short circuit studies are performed several times throughout a project and should be reviewed at least every five years after a project is complete. On a new system, an initial study is performed during the design process to establish the baseline rating of the electrical equipment in the system. This study is typically conservative in nature due to the utilization of calculated values. The final study is performed once the equipment manufacturer has been selected and actual values have been determined. If any changes are made that affect the system, additional studies should be completed.
There are three steps to a performing a short circuit study: the first step is data collection, during which information is gathered on the components of the electrical system, transformer impedances, cable sizes and lengths, manufacturers, utility company information and any other relevant data. The next step is developing a one line diagram, which illustrates the electrical distribution system with the information gathered during the data collection process. Finally, the third step is performing calculations, both manually and through computer analysis. The resulting values are then utilized to determine the interrupt ratings for the electrical distribution equipment within the system. There are many benefits to conducting a short circuit study – it ensures that the system is code compliant, the parameters are set for a safe and reliable electrical distribution system and that personnel can safely operate the system. If you are beginning a project that will require an electricalsystem design or a short circuit study, I encourage you to reach out to see what HAWA can do for you.
