A dynamo electric machine for an aircraft gas turbine engine includes a housing supporting a stator of the dynamo electric machine, a rotor assembly rotatably mounted in the housing and including an elongate hollow rotor shaft, a main shaft for connection at one end to the associated gas turbine engine assembly, said main shaft extending coaxially within said hollow rotor shaft, and a sleeve-like member of electrically insulating material between said rotor shaft and said main shaft, said sleeve-like member providing an electrically insulating driving connection between said main shaft and said rotor shaft whereby said main shaft and said rotor shaft rotate together.