The vacuum circuit breaker has fascinated the switchgear designer for many years, primarily because of the great advantages of vacuum interrupters, which are: (a) They are entirely self contained, need no supplies of gases or liquids and emit no flame or gas. (b) They require no maintenance and in most applications their life will be as long as the circuit breaker in which they are applied. (c) They may be used in any orientation. (d) They are not flammable. (e) They have a very high commutating ability and need no capacitors or resistors to interrupt short line faults. (f) They require a relatively small mechanical energy to operate them. (g) They are silent in operation.