Predicting Damage from 277-V Single Phase to Ground Arcing Faults

Laboratory tests of arcing faults trapped between a corner of a simulated steel housing and single or multiple bus bars were found to be reasonably reproducible and caused relatively consistent burning damage. Single phase 277-V arcing fault tests using spacings of 1 to 4 in from bus bars to ground at current levels of about 3000 to 26 000 A indicate that damage is proportional to I1.5t. In this ``ballpark'' arc voltage and arc length need not be known to predict probable maximum damage. For coordinated short circuit and ground fault protection, an arbitrary practical limit is proposed such that I1.5t is numerically not greater than 250 times the ampere rating of the circuit. Probable maximum burning damage in cubic inches of copper, aluminum, and steel is predicted based on the tests. The arbitrary limit is achievable with commercially available equipment using simple time current band coordination. Lower limits can be achieved using more sophisticated ground fault protection equipment.