Accessory kit for retrofitting of a LV or MV switchgear with an electronic device comprising: - first and second clamping elements (3, 4) mechanically coupleable with a cabinet door of said switchgear at an external surface and an internal surface of said cabinet door, respectively; - at least a support element mechanically coupleable with said second clamping element and with a main unit of said electronic device; - first fixing elements to fix said first and second clamping elements (3, 4) with said cabinet door, said first and second clamping elements comprising first and second mechanical connection points (36, 46) for mechanical coupling with said first fixing elements, respectively; - second fixing elements to fix said support element with said second clamping element, said second clamping element comprising third mechanical connection points for mechanical coupling with said second fixing elements, said support element comprising fourth mechanical connection points for mechanical coupling with said second fixing elements; - third fixing elements to fix the main unit of said electronic device with said support element, said support element comprising fifth mechanical connection points for mechanical coupling with said third fixing elements; characterised in that: - said first clamping element comprises a first clamping plate having opposite first and second coupling surfaces (31, 32), said first clamping plate being mechanically coupleable with the external surface of said cabinet door at said first coupling surface, said first clamping plate comprising first connection holes for the passage of said first fixing elements through said first clamping plate at said first mechanical connection points; - said second clamping element comprises a second clamping plate having opposite third and fourth coupling surfaces (41, 42), said second clamping plate being mechanically coupleable with the internal surface of said cabinet door at said third coupling surface, said second clamping plate comprising second connection holes for the passage of said first fixing elements through said second clamping plate at said second mechanical connection points; - said at least a support element comprises at least a support bracket comprising one or more fifth coupling surfaces, at which said support bracket is mechanically coupleable with said second clamping element, and one or more sixth coupling surfaces, at which said support bracket is mechanically coupleable with the main unit of said electronic device, said at least a support bracket comprising third connection holes for the passage of said second fixing elements through said support bracket at said fourth mechanical connection points and fourth connection holes for the passage of said third fixing elements through said support bracket at said fifth mechanical connection points. - first and second clamping elements (3, 4) mechanically coupleable with a cabinet door of said switchgear at an external surface and an internal surface of said cabinet door, respectively; - at least a support element mechanically coupleable with said second clamping element and with a main unit of said electronic device; - first fixing elements to fix said first and second clamping elements (3, 4) with said cabinet door, said first and second clamping elements comprising first and second mechanical connection points (36, 46) for mechanical coupling with said first fixing elements, respectively; - second fixing elements to fix said support element with said second clamping element, said second clamping element comprising third mechanical connection points for mechanical coupling with said second fixing elements, said support element comprising fourth mechanical connection points for mechanical coupling with said second fixing elements; - third fixing elements to fix the main unit of said electronic device with said support element, said support element comprising fifth mechanical connection points for mechanical coupling with said third fixing elements; - said first clamping element comprises a first clamping plate having opposite first and second coupling surfaces (31, 32), said first clamping plate being mechanically coupleable with the external surface of said cabinet door at said first coupling surface, said first clamping plate comprising first connection holes for the passage of said first fixing elements through said first clamping plate at said first mechanical connection points; - said second clamping element comprises a second clamping plate having opposite third and fourth coupling surfaces (41, 42), said second clamping plate being mechanically coupleable with the internal surface of said cabinet door at said third coupling surface, said second clamping plate comprising second connection holes for the passage of said first fixing elements through said second clamping plate at said second mechanical connection points; - said at least a support element comprises at least a support bracket comprising one or more fifth coupling surfaces, at which said support bracket is mechanically coupleable with said second clamping element, and one or more sixth coupling surfaces, at which said support bracket is mechanically coupleable with the main unit of said electronic device, said at least a support bracket comprising third connection holes for the passage of said second fixing elements through said support bracket at said fourth mechanical connection points and fourth connection holes for the passage of said third fixing elements through said support bracket at said fifth mechanical connection points.