Connecting piece of tray-type wire cable channelling sections consisting of U-shaped cross wire bars with a central branch and side branches, and longitudinal wire bars (V11, V12) that comprise the side walls of the channel sections, as well as longitudinal wire bars forming the bottom wall of such channel section, such connecting piece being provided with a front part and a rear part, to tightly fit the cross wire bars (Vt1-Vt2)) located at the ends of two adjacent cable channelling sections (B, B), such rear part being generally configured with a W-shaped cross-section, having: - two longitudinal grooves with a C-shaped cross-section, where the said wire bars are fitted; - a central portion which extends and connects the corresponding longitudinal grooves; and - corresponding flanges that extend from the outer edges of the relevant longitudinal grooves to be tangentially overlapped at the peripheral area of such wire crossbars of the relevant cable channel section, Where: - such connecting piece is generally configured in the shape of an U with a central branch which extends practically covering the whole length of the relevant central branch of the cross wire bars; and the corresponding side branches that form an angle with the central branch, which is equal to, or greater than the angle formed by the side branches and the central branch of the crossbars of the cable channelling, and each one of the side branches is extended covering the corresponding side branch of the cross wire bars except in the vicinity of the ends of such crossbars; - The length of the flanges corresponding to the side branches of such connecting piece is equal to or smaller than the transverse distance between adjacent longitudinal bars (V11, V12) of the cable channelling, where the said flanges are configured with a lower bevel edge inclined downwards, which allows the fitting between the bars (V11, V12) and the connecting piece and acts as an upper stop to avoid the demounting of the connection when vertical forces are applied in an upwards direction. characterized in that: - the length of the side branches of the connecting piece is chosen so that when the said connecting piece is fitted in the side branches of the relevant crossbar, their free end is located below and distant from the end of the longitudinal wire bar located immediately above, so that they are not in contact; - at least a window-shaped notch is foreseen at the central portion of the side branches, whose length has been selected so that the ends of the intermediate longitudinal wire bars of the relevant adjacent channelling sections (B, B) do not touch the side branch; and - a series of respective notches have been foreseen at the central portion of the central branch of the connecting piece so that the ends of the longitudinal wire bars that form the bottom wall of two adjacent cable channelling sections (B, B) may pass through them without contact. - two longitudinal grooves with a C-shaped cross-section, where the said wire bars are fitted; - a central portion which extends and connects the corresponding longitudinal grooves; and - corresponding flanges that extend from the outer edges of the relevant longitudinal grooves to be tangentially overlapped at the peripheral area of such wire crossbars of the relevant cable channel section, - such connecting piece is generally configured in the shape of an U with a central branch which extends practically covering the whole length of the relevant central branch of the cross wire bars; and the corresponding side branches that form an angle with the central branch, which is equal to, or greater than the angle formed by the side branches and the central branch of the crossbars of the cable channelling, and each one of the side branches is extended covering the corresponding side branch of the cross wire bars except in the vicinity of the ends of such crossbars; - The length of the flanges corresponding to the side branches of such connecting piece is equal to or smaller than the transverse distance between adjacent longitudinal bars (V11, V12) of the cable channelling, where the said flanges are configured with a lower bevel edge inclined downwards, which allows the fitting between the bars (V11, V12) and the connecting piece and acts as an upper stop to avoid the demounting of the connection when vertical forces are applied in an upwards direction. - the length of the side branches of the connecting piece is chosen so that when the said connecting piece is fitted in the side branches of the relevant crossbar, their free end is located below and distant from the end of the longitudinal wire bar located immediately above, so that they are not in contact; - at least a window-shaped notch is foreseen at the central portion of the side branches, whose length has been selected so that the ends of the intermediate longitudinal wire bars of the relevant adjacent channelling sections (B, B) do not touch the side branch; and - a series of respective notches have been foreseen at the central portion of the central branch of the connecting piece so that the ends of the longitudinal wire bars that form the bottom wall of two adjacent cable channelling sections (B, B) may pass through them without contact.