Secondary Arc
Definition
Arc damage created after a fire was already burning, caused by the fire melting insulation and shorting conductors. These markers are consequences of the fire, not causes.
- Cause
- Fire-induced insulation melting and conductor shorting
- Timing
- Occurs after the fire was already burning
- Causal role
- Consequence of the fire, not its cause
- Field
- Electrical fire failure analysis
Common questions
Why is it crucial to tell a secondary arc apart from an arc that started the fire?+
Misidentifying a secondary arc as the ignition source can send an entire investigation toward the wrong cause and wrong point of origin, so investigators cross-reference arc site location against the established burn pattern and fire spread timeline before attributing causal significance to any arc site.
What physical evidence distinguishes a secondary arc from an arc that caused the fire?+
Arc mapping compares the location and severity of multiple arc sites against the overall fire damage pattern; arcs found deep within an area of heavy fire damage, consistent with insulation failing well after flames arrived, are read as secondary, while an arc found at or before the point the fire pattern indicates as origin is a stronger candidate for causal significance.
Can a secondary arc still be useful evidence even though it did not cause the fire?+
Yes, mapping the full set of secondary arc sites helps investigators reconstruct how and in what direction the fire spread through a structure's wiring, which supports the overall origin and cause narrative even though none of those individual arcs started the fire.
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...
- Primary Arc
- An arc that preceded and caused the fire. Its markers on copper conductors appear before any fire damage has reached that location.