Notching
Definition
A V-shaped or crescent-shaped indentation in copper at an arc site, caused by localised material ejection during the arc event. Notching on a conductor that was not exposed to fire is strong evidence of a primary arc.
- Shape
- V-shaped or crescent-shaped indentation
- Location
- Copper conductor at the arc site
- Cause
- Localised material ejection during an arc event
- Significance
- Strong indicator of a primary (fire-causing) arc
Common questions
How does notching help distinguish a primary arc from a secondary one?+
A primary arc occurs on wiring that was still energised and undamaged when the fire started, so notching found on a conductor with no surrounding fire or heat damage points to that arc as an early event, unlikely to be a later consequence of the fire itself.
Can notching be confused with ordinary fire damage to a wire?+
General fire exposure tends to produce more uniform beading, melting, or oxidation along a conductor, while notching is a discrete, localised gouge from the arc's own energy, so examiners look for that localisation and lack of surrounding fire damage together.
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...
- 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...