Abstract: A telescopic boom for a crane, access or load platform or the like, having power transmission lines extending along the boom to its head. In order to avoid problems which arise with such power lines when the bottom is extended or retracted the invention proposes the use of a flexible carrier which extends between a point at the outer end of the base section and a point mid way along the extended sections of the boom between the head and the end of the base section. This enables the power lines to be protected both when the boom is extended and when it is retracted.