Understanding the Effect of Electrode Configuration on Incident Energy and Arc-Flash Boundary

The 2018 update to the IEEE Std. 1584 Guide for Performing Arc-Flash Hazard Calculations has introduced new electrode configurations that can drastically affect incident energy calculations and labeling. The electrode configurations discussed in this article are: vertical conductors/electrodes inside a metal box/enclosure (VCB), vertical conductors/electrodes terminated in an insulating barrier inside a metal box/enclosure (VCBB), and horizontal conductors/electrodes inside a metal box/enclosure (HCB). It is generally understood that at typical working distances, HCB will produce a higher incident energy than VCBB, which will produce a higher incident energy than VCB with all other parameters equal. However, there is a counter-intuitive trend for the arc-flash boundary, such that the boundary distance for HCB is often lower than the boundary for VCBB and VCB. The electrode configuration will also affect the magnitude of arcing current, which may result in varying fault clearing times depending on which electrode configuration is selected. This article will discuss arcing fault current, incident energy, and arc-flash boundary results for each enclosed electrode configuration that challenge the assumption that HCB will always yield the worst-case incident energy and arc-flash boundary. The results of 50 arc flash studies have been surveyed and presented in this article to supplement and validate observations and conclusions.