Electrical Fires: Electrical arcs, what are they?

Technical description

An electric arc is a self-sustained discharge of electrical energy, having a low voltage drop capable of supporting the conduction of large electrical currents. An electrical arc is established either by the separation of electrodes, generally moving contacts of a switch or circuit breaker, or by a transition from a higher voltage discharge.

Whenever two electrodes or the contacts of a switch carrying a current are separated, and arc is established given the high electrical field existing between the electrodes/contacts and local heating at the last point of physical connection, provided that a necessary minimum voltage exists within the parent electrical circuit.

The duration of the electrical arc depends upon the nature of the electrodes, the velocity of the gap evolving between the two electrodes, the nature of the surrounding medium and the properties of the parent electrical circuit.

Simplified Description

Electrical arcing in simple terms is the conduction of electricity through air. Electrical arcing on a small scale is akin to large scale weather ‘bolts’ of lightening.

Electrical arcing occurs when a high energy electrical charge potential which exists between two electrodes (exposed conductors/cores of a cable) and as such ionises the air between the electrodes (breakdown the atomic structure of air) so that the air conducts electrical energy.

Electrical arcing is characterised by the emission of intense blue white light (and a pressure wave due to the rapid thermal expansion of the air.


Eur Ing Dr Robert Brown (Robert) is the Executive Director of Fraser George and Associates Limited and is a Consultant and Forensic Engineer in the fields Electrical Electronic and Control Engineering.


Robert is an accomplished professional Expert Witness having prepared and presented many court compliant reports and presented oral evidence within the High Court, Crown Courts and County Courts.


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