Arcing faults are commonly caused by the following:
- Foreign tools dropped into equipment that may cause short circuit, produce sparks and initiate arcs .
- Entry of foreign bodies(rodent, snake, squirrel).
- Misalignment of moving contacts and corrosion of equipment parts. This weakens the contact between conductor terminals and increases the contact resistance. So heat is generated on the contacts, and sparks may be produced leading to arcing faults with nearby exposed conductors.
- Dirt contamination or dielectric breakdown.dirt on insulating surfaces can provide a path for current, allowing it to ﬂash over, creating arc discharge across the surface. The ﬂash over can also be created by condensation of vapor and water dripping on insulating surfaces.
- Careless cover or device removal that gives an opportunity for accidental touching, with live exposed parts producing arc faults.
- Over voltage across narrow gaps. If the air gap between conductors of phases or phase conductor and earth is narrow enough,the electric field intensity through the air gap may ionize the air during over voltages, producing arc faults.
- Improper maintenance procedures.
Pic show arcflash propagation in a switchgear.