Abstract: A three-pole apparatus, configured to be installed in a cubicle of an electric substation, comprises an air-insulated three-pole disconnector and a three-pole circuit breaker. The air-insulated three-pole disconnector is configured to isolate an electric line leaving the cubicle. The three-pole circuit breaker is configured to perform line protection functions. The three-pole apparatus comprises a casing comprised of insulating material and internally housing, at least partially, the three-pole circuit breaker. The casing is not sealingly closed and contains air. The circuit breaker comprises three vacuum circuit-breaker modules; the disconnector comprises three single-pole disconnector devices. Each of the single-pole disconnector devices in turn comprises a contact movable linearly from a service position into a disconnection position. Each of the contacts, when it is in its service position, projects at least partially from the casing.