Written by Steve Hudgik
An electric arc happens when there is a flow of electrical current between two electrical conductors separated by a gap. The gap is filled with a material that is normally an insulting material such as air. The electric arc typically creates a ionized conductive plasma, extreme heat and bright light.
An electric arc may be intentionally created and used for useful purposes such as arc lights, welding and electric furnaces. An electric arc may also be created unintentionally and be harmful such as when there is an arc flash or arc blast.
You may not be aware of it, but low energy electric arcs are used all around you. Fluorescent lighting, and mercury and sodium street lights use low energy electric arcs to create light. The bright light from a camera or cell phone flash comes from a low energy electric arc.
Small electric arcs are now even being used for surgery, replacing scalpels.
High energy electric arcs are used for electric discharge machining, for arc welding and for creating intense heat in industrial electric furnaces. Electric furnaces have the ability to rapidly start up and change to adapt to changing loads. This makes them ideal for steel mills that need to frequently change production to adapt to customer needs. The intense heat created by an electric arc also makes electric furnaces the preferred technology for making substances, such as calcium carbide, that require large amounts of energy to manufacture.
The intensity, brightness and temperature of an electric arc is controlled using several factors, such as:
For an arc to form the gas between the electrodes must become an ionized plasma. The type of gas used, and its pressure, will changes the characteristics of the arc. That affects the brightness, color and the amount of heat produced by the arc.
An undesired electric arc is one that occurs in a location where it was not intended for an electric arc to happen. This might be in an electrical switch yard; in a circuit breaker; or when an electrical cable is damaged. Unintended electric arcs can cause damage to equipment and may injure or be fatal to people who are working on the equipment or even are just nearby.
An arc flash is a very short but extremely intense electric arc that may have explosive characteristics. The resulting heat is so intense that conductors may be vaporized. The metal vapor and molten metal will be blasted into the surrounding area. In addition to injuries from the blast, anyone close by will breath in the hot metal vapor and their lungs will be burned.
An arc flash, also known as an arc blast, happens very quickly and unexpectedly. Anyone working on equipment that has the potential for an arc flash must be using appropriate precautions and be protected by appropriate PPE.
Electric arc hazards are invisible. That means labels and signs are needed to warn people away from electrically hazardous areas. Labels and signs inform workers about the need to be a qualified person before entering certain areas or working on electrical equipment. Labels and signs inform electrical workers about needed PPE.
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The information presented in this document was obtained from sources that we deem reliable; Graphic Products does not guarantee accuracy or completeness. Graphic Products, Inc. makes no representations or warranties of any kind, express or implied. Users of this document should consult municipal, state, and federal code and/or verify all information with the appropriate regulatory agency.