In electronics, electrical breakdown or dielectric breakdown is a process that occurs when an electrically insulating material, subjected to a high enough voltage, suddenly becomes a conductor and current flows through it. All insulating materials undergo breakdown when the electric field caused by an applied voltage exceeds the material's dielectric strength. The voltage at which a given insulating object becomes conductive is called its breakdown voltage and, in addition to its dielectric strength, depends on its size and shape, and the location on the object at which the voltage is applied. Under sufficient voltage, electrical breakdown can occur within solids, liquids, or gases. However, the specific breakdown mechanisms are different for each kind of dielectric medium.
Electrical breakdown in an electric discharge showing the ribbon-like plasma filaments from a Tesla coil.
A Tesla coil, showing several forms of electrical breakdown. On the right side of the aluminum high voltage terminal (top right) is a purple corona discharge. At the end of the wire projecting from the terminal (top left) is a brush discharge. The fluorescent tube lying on the stand is lit by a glow discharge induced by the radio frequency electric field. At bottom the Tesla coil apparatus is lit by an intense white light from an electric arc in a
Dielectric breakdown within a solid insulator can permanently change its appearance and properties. As shown in this Lichtenberg figure
An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and conductors—conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors. The most common examples are non-metals.
Ceramic insulator used on an electrified railway
Three-core copper wire power cable, each core with an individual colour-coded insulating sheath, all contained within an outer protective sheath
PVC-sheathed mineral-insulated copper-clad cable with two conducting cores
Pin-type glass insulator for long-distance open-wire transmission for telephone communication, manufactured for AT&T in the period from c. 1890 to WW-I; It is secured to its support structure with a screw-like metal or wood pin matching the threading in the hollow internal space. The transmission wire is tied into the groove around the insulator just below the dome.