Causes of Arc Flash

An arc flash can be spontaneous or result from inadvertently bridging electrical contacts with a conducting object. Other causes may include dropped tools or the buildup of conductive dust or corrosion. An electric arc flash can occur if a conductive object gets too close to a high-amp current source or by equipment failure (for instance, while opening or closing disconnects).

Conditions under which arc flash can occur:

Human Error, which is considered the most common cause:

  • Dropped or unintentional contact with live circuit with non-insulated tool or conductive object
  • Improper installation of equipment
  • Negligent or improperly done preventive maintenance
  • Failure to de-energize equipment whenever possible

Equipment Failure:

  • Due to failure of electrical equipment and or system design
  • Due to faulty system design


  • Buildup of conductive dust
  • Corrosion
  • Moisture or conductive liquids/vapor
  • Animal contact (rodent, snake, bird, etc.)


A worker was injured while laying block for a surface electrical installation. He was cleaning the mortar joints with a piece of metal conduit when the conduit fell through the top of a 660 VAC panel, causing a short. The ensuing arc burned through the panel access door (Figure 1), the flash inflicting 1st and 2nd degree burns to the worker's arm, face and neck.


Figure 1: Arc Blast Damage in Electrical Cabinet Door