Arcing faults receive an increasing amount of attention as a particularly damaging and potentially dangerous type of fault. The arcing fault is a ﬂash over of low electric current that ﬂows through the air. It releases a great deal of energy in the form of heat and pressure. The temperature can rise to 19,420°C (35,000°F), and the intense heat from the arc can cause a sudden expansion of the air resulting in a blast with very strong air pressure that can vaporize the materials and damage the equipment.
Causes of an Arc Flash
Arc flashes are commonly caused by the following:
1. Foreign tools
Foreign tools dropped into equipment or accidental tool slippage may cause short-circuit, produce sparks, and initiate arcs. A dropped screw or bolt, a tool slipping when he or she applies torque, or a distraction during a critical moment could result in a mistake that leads to the flash.
2. Animals and foreign bodies
Entry of foreign bodies or animals can cause an arc flash. Birds, rodents, snakes, and other animals can inadvertently bridge the space between conductors or cause leads to slapping together, creating an arcing fault.
3. Misalignment and corrosion
Misalignment of moving contacts, corrosion of equipment parts, and other impurities weaken the contact between conductor terminals and increase contact resistance. So, heat is generated on the contacts, and sparks may be produced leading to arcing faults with nearby exposed conductors.
4. Dirt and dielectric breakdown
Dirt on insulating surfaces can provide a path for current, allowing it to ﬂashover creating arc discharge across the surface. The ﬂashover can also be created by condensation of vapor and water dripping on insulating surfaces.
5. Accidental touching
Careless cover or device removal that gives an opportunity for accidental touching with live exposed parts producing arc faults. No matter how well-trained a worker is, accidents happen and are often the result of operator error. It’s estimated that two out of every three arc flash incidents occur as a result of human error and carelessness.
Overvoltages 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 overvoltages producing arc faults.
7. Improper maintenance
Arc flash hazard assessment is a relatively new development in the world. Equipment and work safety standards seek to provide passive protection against shock hazards and although the arc flash hazard is not explicitly addressed, existing measures often can reduce the likelihood of an arc initiation. Despite these measures, the arc flash risk cannot be completely avoided during some work activities due to improper maintenance procedures.
8. Lack of a main protective device
In cases where no incoming protective device is present in the panel or switchgear, or energized parts of the bus are not separated by compartmentalization or barriers, arc fault must be cleared by the protective devices upstream of the panel or switchgear. The effect of relying on an upstream device leads to an increase of incident energy of over four times.