until the fault is cleared by circuit breaker operation. For this reason, non-linear resistors known as varistors can replace arcing horns at critical locations. Switch protection Arcing horns are sometimes installed on air-insulated switchgear and transformers to protect the switch arm from arc damage. When a high voltage switch breaks a circuit, an arc can establish itself between the switch contacts before the current can be interrupted. The horns are designed to endure the arc rather than the contact surfaces of the switch itself. Corona and grading rings Arcing horns are not to be confused with corona rings (or the similar grading rings) which are ring-shaped assemblies surrounding connectors, or other irregular hardware pieces on high potential equipment. Corona rings and grading rings are intended to equalize and redistribute accumulated potential away from components that might be subject to local accumulation and destructive discharges, although sometimes either device may be installed in close proximity to an arcing horn assembly. References Electric power systems components Electric arcs