A busbar power distribution device comprising: - a first busbar duct having a plurality of mutually insulated conductors, extending in a prevailing longitudinal direction, - a second busbar duct having a plurality of mutually insulated conductors, extending in a prevailing longitudinal direction, - junction means for connecting the conductors of the first busbar duct with the corresponding conductors of the second busbar duct, wherein said junction means comprise: - a plurality of pairs of conductor plates, each pair of conductor plates defining a seat for receiving the end portions of the conductors of the first busbar duct and the second busbar duct, - a plurality of insulator plates interposed between the pairs of conductor plates, - first clamping means for clamping said pairs of conductor plates and said insulator plates against an elastic load, - second clamping means that extend through the conductors of at least one of the conductors of the first busbar duct and the conductors of the second busbar duct, characterized in that - the end portions of the conductors of said first and second busbar ducts through which the first and second clamping means extend have aligned closed slots (13,14) that form respective passages (13a, 14a) for said first and second clamping means, - said closed slots (13, 14) extend along portions having a length A, in the longitudinal direction of the respective first and second busbar duct (11, 12), so that the respective first and second busbar ducts (11, 12) may slide relative to said junction means to adjust the distance between the end portions of the conductors of said first and second busbar ducts within a range equal to the sum of the lengths A of said closed slots (13, 14) - a first busbar duct having a plurality of mutually insulated conductors, extending in a prevailing longitudinal direction, - a second busbar duct having a plurality of mutually insulated conductors, extending in a prevailing longitudinal direction, - junction means for connecting the conductors of the first busbar duct with the corresponding conductors of the second busbar duct, - a plurality of pairs of conductor plates, each pair of conductor plates defining a seat for receiving the end portions of the conductors of the first busbar duct and the second busbar duct, - a plurality of insulator plates interposed between the pairs of conductor plates, - first clamping means for clamping said pairs of conductor plates and said insulator plates against an elastic load, - second clamping means that extend through the conductors of at least one of the conductors of the first busbar duct and the conductors of the second busbar duct, characterized in that - the end portions of the conductors of said first and second busbar ducts through which the first and second clamping means extend have aligned closed slots (13,14) that form respective passages (13a, 14a) for said first and second clamping means, - said closed slots (13, 14) extend along portions having a length A, in the longitudinal direction of the respective first and second busbar duct (11, 12), so that the respective first and second busbar ducts (11, 12) may slide relative to said junction means to adjust the distance between the end portions of the conductors of said first and second busbar ducts within a range equal to the sum of the lengths A of said closed slots (13, 14)