Arc Fault
Definition
An unintended electrical discharge across a gap or through degraded insulation that releases energy as heat and light. Arc faults are classified as series (along a conductor) or parallel (between conductors at different potentials).
- Cause
- Discharge across a gap or through degraded insulation
- Energy released as
- Heat and light
- Classification
- Series (along a conductor) or parallel (between conductors)
Common questions
What is the practical difference between a series and a parallel arc fault?+
A series arc occurs along a single damaged conductor, such as a frayed wire, and produces relatively low current that standard breakers may not trip on, whereas a parallel arc jumps between two conductors at different potentials and typically draws higher current that a conventional breaker is more likely to interrupt.
How do investigators confirm an arc fault was the ignition source rather than a consequence of the fire?+
They examine bead location, conductor damage pattern, and burn pattern progression relative to the arc site, since an ignition-causing arc typically sits at or near the fire's origin with beading consistent with pre-fire electrical fault rather than melting from external flame impingement.
Related terms
- AFCI
- Arc-fault circuit interrupter. A device that detects the high-frequency signature of arcing current and opens the circuit. Required by the National Electrical...
- Alloying
- Incorporation of a foreign metal (steel, zinc, aluminium) into a copper arc bead. The arc's intense temperature fuses adjacent metals together. The...
- Notching
- A V-shaped or crescent-shaped indentation in copper at an arc site, caused by localised material ejection during the arc event. Notching on...
- Primary Arc
- An arc that preceded and caused the fire. Its markers on copper conductors appear before any fire damage has reached that location.
- Secondary Arc
- Arc damage created after a fire was already burning, caused by the fire melting insulation and shorting conductors. These markers are consequences...