IEEE Std.1584tm, IEEE Guide for Performing Arc Flash Hazard Calculations defines the practice for performing detailed arc flash calculations. This method has become the currently accepted industry practice used for calculating the prospective incident energy that could be available at a given location which can be used to determine the PPE requirements.
An arc flash calculation study requires calculating the equivalent arcing short circuit current at each location under study. The arcing current is used to evaluate the time current characteristic of the upstream overcurrent device that would interrupt the arc flash. Typically the maximum short circuit current is considered the worst case however, during an arc flash, lower short circuit currents could be worse because the overcurrent device could take longer to operate leading to a greater exposure.
Once the arcing current and clearing time have been established, the IEEE 1584 formulas provide methods to calculate the incident energy in calories / centimeter2 which can be used for the selection of personal protective equipment (PPE). The incident energy, flash protection boundary and category of PPE along with approach limits for shock protection can become part of the detailed arc flash label.
Although NFPA 70E does not mandate calculations be performed according to the IEEE 1584 methods, it is the method most people use.
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