Sections 20-341s to 20-341bb, inclusive, shall not apply to any of the following persons or organizations: (1) The government of the state, municipalities of the state or any department or agency of the state or such municipalities; (2) the government of the United States or any of its departments or agencies; (3) any school, public or private, offering as part of a vocational education program courses and training in any aspect of plumbing and piping work or heating, piping and cooling work; (4) any public service company regulated by the Public Utilities Regulatory Authority or any corporate affiliate of any such company where the work performed by such affiliate is on behalf of a public service company, in either case only if the work performed is in connection with the rendition of public utility service.