Editing Dielectric strength (section)

==Electrical breakdown==
[[Electric current]] is a flow of electrically [[charged particle]]s in a material caused by an [[electric field]].  The mobile charged particles responsible for electric current are called [[charge carrier]]s.  In different substances different particles serve as charge carriers: in metals and other solids some of the outer [[electron]]s of each atom ([[conduction electron]]s) are able to move about the material; in [[electrolyte]]s and [[plasma (physics)|plasma]] it is [[ion]]s, electrically charged [[atom]]s or [[molecule]]s, and electrons.   A substance that has a high concentration of charge carriers available for conduction will conduct a large current with the given electric field created by a given [[voltage]] applied across it, and thus has a low [[electrical resistivity]]; this is called an [[electrical conductor]].  A material that has few charge carriers will conduct very little current with a given electric field and has a high resistivity; this is called an [[electrical insulator]].

However, when a large enough electric field is applied to any insulating substance, at a certain field strength the concentration of charge carriers in the material suddenly increases by many orders of magnitude, so its resistance drops and it becomes a conductor.  This is called ''electrical breakdown''.  The physical mechanism causing breakdown differs in different substances.  In a solid, it usually occurs when the electric field becomes strong enough to pull outer [[valence electron]]s away from their atoms, so they become mobile.    The field strength at which break down occurs is an intrinsic property of the material called its ''dielectric strength''.

In practical [[electric circuit]]s electrical breakdown is often an unwanted occurrence, a failure of insulating material causing a [[short circuit]], resulting in a catastrophic failure of the equipment.   The sudden drop in resistance causes a high current to flow through the material, and the sudden extreme [[Joule heating]] may cause the material or other parts of the circuit to melt or vaporize explosively.  However, breakdown itself is reversible.  If the current supplied by the external circuit is sufficiently limited, no damage is done to the material, and reducing the applied voltage causes a transition back to the material's insulating state.