Electrical Arcing and Electrical Sparking
Electric Spark
An electric spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures.
A discharge of static electricity is an example of a spark discharge as is the spark generated across the electrodes of a car 'spark plug'.
Electrical Arc
In 1801, British Chemist and inventor, Sir Humphry Davy, demonstrated the generation of an electrical arc to his fellows in the London Royal Society, and offered the name, the electrical arc.
Further advances in early electrical arc studies produced such industry-important inventions as arc welders.
Compared to a spark, which is only momentary, an arc discharge is a continuous electrical current that develops so much heat from the charge carrying ions or electrons that it can vaporize or melt anything within the range of the arc.
An arc can be sustained in either DC or AC electrical circuits, and if not checked by protection devices and can proliferate to destroy the actual electrical source which sustains it with the heat and energy draw of the arc.