Brush discharge

Both brush and corona discharges represent local regions next to conductors where due to the high voltage the air has undergone electrical breakdown: it has ionized and become conductive, allowing current to leak into the air.

They occur when the electric field at the conductor exceeds the dielectric strength of the air, the "disruptive potential gradient", roughly 30 kilovolts per centimeter.

Occurring in very high voltage equipment like EHV power transmission lines, radio transmitters and their antennas, CRT power supplies, and power supplies for scientific equipment like lasers and particle accelerators, a brush discharge represents a serious failure of electrical insulation, and may be a fire hazard.

Like other electric arcs, brush discharges produce ozone gas, which can be noxious to nearby people in an enclosed space and over time can cause embrittlement of some plastics.

Brush discharges can occur from charged insulating plastics (for example polyethylene) to a conductor.