Arc Flash Hazard—When Overestimating Underestimates a Problem

When one undertakes an arc flash study, one must develop a model based on the power system of interest. The model requires estimates of conductor lengths and other data. To ensure that the arc flash study that one is performing does not underestimate the magnitudes of the short circuit currents present within the power system, and to allow for limitations in the procedure by which one develops the model, typically visual inspection, one must carefully estimate the lengths of conductors. Computing “safety margins” can help to avoid errors, and maintenance switches can address the uncertainties involved. The final solution may be software that permits the percentage estimates for impedance elements to be built into the model for various equipment and used to compute arc flash levels on the secondaries of low-voltage circuit breakers.