Abstract: Tensioning device suitable for providing an adjustable and balanced tension to the power-supply and multiplexing cable (1) and to the coaxial video transmission cable (2), these being connected up to a camera turret supported by a carriage (C) for to-and-fro translation in a video surveillance tunnel, each of these two cables (1, 2) being anchored in a fixed manner to the carriage (C), as well as to its point (P1, P2) of penetration into the tunnel, coming from outside the latter, and being rigged up over the pulley of a respective tensioning pulley block (M1, M2) before being anchored to the corresponding bracket (S1, S2) of the carriage (C), these two pulley blocks (M1, M2) being connected by a flexible cablet (3) passing over return pulleys (4, 5, 7) and a roller (6) of a tensioning device.