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 . <EOS>