Causes of Electric Flash

Flash can be initiated by the following:

Dust and impurities: Dust and impurities on insulating surfaces can provide a path for current, allowing it to flashover and create arc discharge across the surface. This can develop into greater Flash. The fumes or vapor of chemicals can reduce the breakdown voltage of air and cause arc flash.

Corrosion: Corrosion of equipment parts can provide impurities on insulating surfaces. Corrosion also weakens the contact between conductor terminals, increasing the contact resistance through oxidation or other corrosive contamination. Heat is generated on the contacts and sparks may be produced. This can lead to arcing faults with nearby exposed conductors of a different phase or ground.

Condensation of vapor and dripping water can cause tracking on the surface of insulating materials. This can create a flashover to ground and potential escalation to phase-to-phase arcing.

Accidental touching: Accidental contact with live exposed parts can initiate arc faults.

Dropping tools: Tools dropped accidentally can cause a momentary short circuit, producing sparks and initiating Flash. Over-voltages across narrow gaps: When the air gap between conductors of different phases is very narrow (due to poor workmanship or damage of the insulating materials), Flash may strike across during over-voltages.

Failure of the insulating materials.

Electric Flash are also caused by the following:

Electric Flash produce some of the highest temperatures known to occur on earth— up to 35,000 degrees Fahrenheit.3 This is four times the surface temperature of the sun.

The intense heat from an arc causes the sudden expansion of air. This results in a blast with very strong air pressure (lightning is a natural arc). All known materials are vaporized at this temperature. When materials vaporize they expand in volume (copper— 67,000 times, water—1,670 times4). The air blast can spread molten metal to great distances with force.

For a low voltage system (480/277 V), a 3 to 4-inch arc can become “stabilized” and persist for an extended period of time. The energy released is a function of system voltage, fault current magnitude, and fault duration. Flash in enclosures, such as in a motor control center (MCC) or switchgear, magnify the blast and energy transmitted as the blast is forced to the open side of the enclosure and towards the worker.

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