Location: AC Arc Flash Defined

What is an ARC Flash, and Why do I care?

Arc Flash is a short circuit, or arc, that flashes from one live conductor to another or ground. As the arc flashes, the air surrounding the arc is superheated, resulting in ionized air that is both electrically conductive and a superheated plasma. The character of an arc flash blast is quite different from a chemical explosion, as there is much more heat and light, without the majority of the mechanical shock. However, the resulting devastation from an ARC Flash event is comparable. The rapidly expanding superheated vapor produced by the arc can cause serious injury and or damage via:

The intense UV, visible, and IR light produced by the arc can temporarily and sometimes even permanently blind or cause eye damage to people. As the light contacts surfaces, it is so powerful it ablates many surfaces. As IR and UV light comes in contact with surfaces, it is transformed into intense heat.

The air temperatures. Air can reach temperatures of 5000F and above almost instantaneously in an ARC event. The arc flash explosion takes less than one second and produces a brilliant flash of both light and heat as the current arcs through the plasma. The intense heat isn't the only danger though.

The massive energy and high heat produced by the arc fault rapidly vaporizes the metal conductors involved. As the conductors are melted, molten metal and expanding plasma are moved outward with extreme force.

In addition, arc flash creates a pressure blast equivalent to several sticks of dynamite. As an example of the energy released in an arc flash incident, consider a single phase-to-phase fault on a 480 V system with 20,000 amps of fault current. The resulting power is 9.6 MW. If the fault lasts for 10 cycles at 60 Hz, the resulting energy would be 1.6 megajoules. For comparison, TNT releases 2175 J/g or more when detonated (a conventional value of 4,184 J/g is used for TNT equivalent). Thus, this fault energy is equivalent to 380 grams (approximately 0.8 pounds) of TNT.

How do you avoid an arc flash?
Isolate conductors and circuits.!
Keep your sine waves separate!
Use UL Listed Equipment!
Install equipment to NEC standards!

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