Section 7. This chapter shall not apply to: the installation, repairing, and wiring of elevators; the work in connection with the erection, construction, maintenance or repair of lines for transmission of electricity from the source of supply to the service switch on the premises where used by municipal electric plants, by electric companies as defined in section one of chapter one hundred and sixty-four, by gas companies authorized to make or sell electricity, by electric street railway companies, by electric railroad companies or by railroad companies; the work of such plants or companies on premises owned or controlled by them; the work of said municipal electric plants or of said electric or gas companies in installing, maintaining and repairing on the premises of customers, service connections and meters and other apparatus and appliances remaining the property of such plants or companies after installation; public employees engaged in the work of installing, maintaining or repairing public signalling systems; the work in connection with the lighting of public ways, alleys, private ways, or public parks, areas or squares; the work of companies subject to regulation by the department of public utilities or the department of telecommunications and cable, and incorporated for the transmission of intelligence by electricity in installing, maintaining or repairing wires, apparatus, fixtures, or other appliances used by such companies and necessary for, or incident to, their business, whether or not such wires, conduits, apparatus, fixtures or other appliances are on its own premises; or the work in connection with the installation, construction, maintenance, repair and renovation of telephone equipment, cable television service or computer systems by a person, firm or corporation primarily engaged in the telecommunications or the information systems industry.