![]() The HCB model is representative of large power circuit breaker cubicles in switchgear, junction boxes, and some disconnects versus what is typically found in smaller panelboards (VCB/VCBB). The HCB calculations result in a significantly higher incident energy than the VCB/VCBB calculated energies and the energy calculated under the 2002 model when considering a typical range of bolted fault current values. 2018 IE Calculated Result Comparison at 480 V The following parameters were used in the analysis:įigure 2: 2002 vs. As a result of using a fixed duration for the calculations, the reduced arcing current calculation was not applicable for this analysis. For the following examples, a fixed duration time of 83.3 ms (5 cycles) was used. Designed interruption times for molded-case circuit breakers are approximately 8.33 ms (1/2 cycle) and 50 ms (3 cycles) for power circuit breakers. For both scenarios, a fixed event duration of 83.3 ms was used. The first is a 208 V system the second is a 480 V system. The comparison focuses on low-voltage systems, as these are the most prevalent systems workers are exposed to, and this is where most accidents occur. While many variables must be considered when comparing the two methods, I’ve put together some scenarios that provide a practical comparison that answers these questions. Will the new calculations result in significantly different incident energy (IE) values?.How do the old and new methods compare with respect to incident energy calculations, and how significant are these changes to the results of the analysis?.Does a new study need to be performed using the new method?.Let’s start by considering the most frequently asked questions related to this new arc flash calculation process: In Part 2, we discuss the relevant impact of these changes and how they affect the calculated incident energy levels that we depend on to select adequate PPE and keep our workers safe. We also reviewed some of the key changes from the original 2002 edition of IEEE 1584 to the second edition in 2018, specifically examining the newly recommended arc flash calculation process and variables included in the calculations. It was during this period that OSHA was formed and NFPA began developing the 70E standard. ![]() In the Spring 2022 edition of NETA World, Part 1 of this article provided a brief history and evolution of electrical safety over the past 50 years. ![]()
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