An accessory device for a medium-voltage vacuum contactor, wherein said vacuum contactor comprises two or more electric poles, each comprising an open insulating casing and a vacuum bottle accommodated in an internal space defined by said insulating casing, whereby said accessory device comprises a first support member, a second support member, characterised in that said accessory device comprises a plurality of third support members and one or more clamping members, wherein, when said accessory device is installed on said vacuum contactor: - said first support member is coupled to the insulating casing of each electric pole, at a first side of said insulating casing; - said second support member is coupled to the insulating casing of each electric pole, at a second side of said insulating casing opposite to said first side; - each third support member is placed at a lateral flank of the insulating casing of an electric pole, said third support members being arranged transversally to said first and second members and joined to said first and second members, - each clamping member is partially accommodated in the internal space of a corresponding electric pole and is coupled to the vacuum bottle of said corresponding electric pole, wherein, when said accessory device is installed on said vacuum contactor, each camping member is joined to said second support member. wherein said vacuum contactor comprises two or more electric poles, each comprising an open insulating casing and a vacuum bottle accommodated in an internal space defined by said insulating casing, whereby said accessory device comprises a first support member, a second support member, characterised in that said accessory device comprises a plurality of third support members and one or more clamping members, wherein, when said accessory device is installed on said vacuum contactor: - said first support member is coupled to the insulating casing of each electric pole, at a first side of said insulating casing; - said second support member is coupled to the insulating casing of each electric pole, at a second side of said insulating casing opposite to said first side; - each third support member is placed at a lateral flank of the insulating casing of an electric pole, said third support members being arranged transversally to said first and second members and joined to said first and second members, - each clamping member is partially accommodated in the internal space of a corresponding electric pole and is coupled to the vacuum bottle of said corresponding electric pole, - said first support member is coupled to the insulating casing of each electric pole, at a first side of said insulating casing; - said second support member is coupled to the insulating casing of each electric pole, at a second side of said insulating casing opposite to said first side; - each third support member is placed at a lateral flank of the insulating casing of an electric pole, said third support members being arranged transversally to said first and second members and joined to said first and second members, - each clamping member is partially accommodated in the internal space of a corresponding electric pole and is coupled to the vacuum bottle of said corresponding electric pole, wherein, when said accessory device is installed on said vacuum contactor, each camping member is joined to said second support member.