Primary Arc
Definition
An arc that preceded and caused the fire. Its markers on copper conductors appear before any fire damage has reached that location.
- Definition
- An arc that preceded and caused the fire
- Location on conductor
- At the point of ignition, ahead of fire spread
- Contrast
- Secondary arcs occur after fire damage reaches the wire
- Diagnostic use
- Helps pinpoint the fire's area of origin
Common questions
How is a primary arc distinguished from a secondary arc on the same wire?+
Examiners map the location and sequence of arc beads against the fire spread pattern and structural damage; an arc bead found where insulation had not yet been compromised by external fire heat is treated as primary, while beads at points reached later by the fire are treated as secondary.
Why does finding a primary arc matter for the fire investigation?+
A primary arc site is a strong indicator of the fire's origin, because the electrical fault occurred there before the fire spread outward, which helps investigators separate the ignition source from damage that fire itself later caused to other wiring nearby.
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...
- Arc Fault
- An unintended electrical discharge across a gap or through degraded insulation that releases energy as heat and light. Arc faults are classified...
- 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...
- Secondary Arc
- Arc damage created after a fire was already burning, caused by the fire melting insulation and shorting conductors. These markers are consequences...