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nited <br />eevices <br />roup~' <br />ARC FLASH HAZARD TIME-CURRENT CURVES FOR <br />ELK RIVER MUNICIPAL UTILITIES <br />Zi2oios <br />The following arc flash hazard time-current curves (TCCs) illustrate the arc flash hazard <br />category at .various points on the TCC for selected fuses and protective devices. <br />Analysis was performed at both 15" (381 mm), equivalent to doing work with ones <br />hands, and 8' (2440mm), equivalent to doing work with a hotstick /shotgun stick. In <br />creating these curves, defined fault current values were used as opposed to the infinite <br />bus bolted fault calculations and the resultant calculated arcing fault current. Given the <br />selected fault current value, the protective device's total clear time was input into the <br />IEEE 1584 spreadsheet resulting in arc flash hazard category for the given fault current. <br />For current values between that shown on the TCC, the arc flash hazard category <br />should be assumed to be the higher of the two hazard categories. <br />It can be seen that many fuses have an arc flash hazard category greater than 2. While <br />these results are accurate for the illustrated fault currents, for many protective device <br />locations a fault with a magnitude less than 500A is uncommon. In many cases, <br />especially with underground conductor, fault currents that we have seen are at least <br />50% of the maximum available fault current at a given location. <br />When consulting arc flash hazard TCCs to deduce the arc flash hazard risk category at <br />a given location, remember that it is the fuse upstream of the arcing point that will likely <br />clear the fault. For example, if replacing an 80T fuse reference the TCC for the <br />protective device upstream of the 80T fuse. <br />1 of 1 <br />