Short Circuit Coordination

  • A Short Circuit Coordination Study is critical for the safe, efficient and economical operation of any electrical distribution system. A Short Circuit Study will help to ensure that personnel and equipment are protected by establishing proper interrupting ratings of protective devices (circuit breaker and fuses). If an electrical fault exceeds the interrupting rating of the protective device, the consequences can be devastating, including injury, damaged electrical equipment and costly downtime.
     
  • A Short Circuit and Coordination Study is a very important, yet sometimes overlooked step after the initial design and before the implementation of an electrical distribution system. The NEC addresses the importance of this type of study in articles 110-9, 110-10, 240 and 517.17. It is clear that a third party, independent study performed during/after the equipment submittal process, can prove to be invaluable. A Short Circuit and Coordination Study serves to incorporate all the system changes that come about after the initial design. Some examples of factors that commonly change in the implementation of a system are: the utility available fault level, size and or transformer impedance values, conductor size/type, addition of motors and the system operating parameters.
     

  • Circuit breakers and fuses come with an overcurrent rating (or size), and a short circuit interrupting rating. The overcurrent rating specifies the amount of electrical current the device should tolerate without the fuse blown, or circuit breaker tripping. The short circuit rating is the maximum electrical current the device can tolerate before it fails.
     
  • A Coordination Study maximizes power system selectivity by isolating faults to the nearest protective device, as well as helping to avoid nuisance operations that are due to transformer inrush or motor starting operations.