Voltages above ______ have sufficient energy to sustain arcing and to create severe blast conditions.

• A. 12 volts
• B. 600 volts
• C. 120 volts
• D. 240 volts

Answer: (C)

Arcs occur when the electric field between conductors ionizes the surrounding air, creating a plasma path for current. When a fault drives current through that path, the arc energy can heat the air and surrounding materials, producing a rapid pressure rise and potentially a powerful blast. Once voltage reaches about 120 volts, the conditions are frequently enough that an air gap can break down and sustain an arc if a conductive path exists. At lower voltages like 12 volts, sustaining an air arc is unlikely in normal conditions; at higher voltages such as 240 or 600 volts, arcing and associated blast effects are even more likely, but 120 volts is the commonly referenced threshold for when arcing energy becomes significant enough to sustain and cause severe effects.