The Nature of the Electrical Arc Event
- Electrical arcs produce some of the highest recorded temperatures known to occur on the earth, up to 35000 degrees Farenheit.
- This is 4 times the surface temperature of the sun!
- This intense heat from the arc causes a sudden expansion of super heated air. Resulting in an arc blast with very strong pressure.
- All known materials are vaporized at this temperature. When something is vaporized it expands in volume for copper it is 67000 times, water is 1670 times
- Arc occuring inside an electrical cabinet are increased, as the blast is focused out of the only opening in the enclosure, which is where the worker usually is standing.
Arc Flash as stated in CSA Z462, Canadian electrical code, Occupational Health and Safety Act, and regulations, NFPA-70E and IEEE std 1584-2002 is dealing with personal injury to a worker(s) who is engaged in work activities near to, or directly on electrically energized equipment. Working on energized conductors should only be done as a last resort, when no other option is availiable. When work is performed on energized equipment, a live work permit needs to be issued, this includes a signature from Management!The proper Personal Protective Equipment (PPE), this consists of Fire Retardant Clothing, Face Shield and Approved Voltage rated glove combination. Adanac Electric Inc. does not endorse working on energized equipment.
Causes of Electric Arcs
Arcs can be caused by the following:
- Glow to arc discharge:
- Dust and other impurities: Dust and impurities on insulating material surfaces can provide a pathway for electrical current to flow, creating a flashover and the ensuing arc blast
- Corrosion: Corrosion of Conductors and equipment can provide impurities across insulating surfaces. Corrosion also weakens the contacting terminals(less surface area due to pitting, oxidation or corrosive contamination) this increases the resistance, generating excess heat where sparks can be produced, leading to arcing faults to ground and any nearby exposed conductors of different phase, or neutral.
- Failure of Insulating Materials
- Overvoltages across narrow gaps due to damaged insulation, improper installation, arcs are more likely to be produced in an overvoltage event.
- Condensation of vapor and dripping water can introduce impurities tracking across the surface of insulating materials creating a flashover to ground or to an opposing phase.
- Spark Discharge due to accidental touching, or dropping tools or other conductive material across phases, or phase to ground/neutral.
Hazards of arcing events:
- Pressure: Arc flash blast waves throw workers across rooms, and knock over ladders workers were standing on. Chest level pressures can reach 2000lbs/sq foot
- Shrapnel: can penetrate the body, including moltant metal flying outward at high pressures.
- Heat: Fatal burns have occured when the worker has been more than 10 ft from the blast(serious burns are common at a 10ft distance). Non Fire resistant clothing can immediatly ignite from several feet away. Clothed areas can be burned more severely than exposed skin.
- Sound: Hearing loss from an arc blast is an issue as well, due to the fact that the sound can be as loud as 140 db at a distance of 2 feet from the arc.
