An arcing fault is a dangerous electrical event that can occur anywhere in an electrical system when the conductors or wires are damaged creating a fire hazard.
Wires can become damaged during installation & home construction, from homeowners penetrating them with screws or nails, or while hanging shelves and pictures. Other causes include using damaged extension cords or appliances that are not compliant with U.S. electrical safety codes.
A series arc is a dangerous transfer of electrical energy across a broken wire or conductor.
A parallel arc is a dangerous transfer of electrical energy across multiple conductors
Actual laboratory result of an arc fault due to a screw for a shelf bracket penetrating the flexible wire