Abstract: A telescopic boom assembly is disclosed. The assembly includes a plurality of boom members having at least first, second and third boom arms telescopically disposed within each other. The first boom arm is connected to a support base. A mechanism is provided for axially extending the second and third boom arms outwardly from the first boom arm, the third boom arm being constructed from dielectric material and disposed at the distal end of the assembly once the assembly is in a fully extended position. Finally, an end cylinder structure constructed from dielectric material is provided for axially moving the third boom arm relative to the first and second boom arms such that the third boom arm and the end cylinder structure dielectrically insulate the distal end of the third boom arm from the remainder of the boom assembly when the assembly is in an extended condition.