The provisions of this chapter shall not apply to (1) persons employed by any federal, state or municipal agency; (2) employees of any public service company regulated by the Public Utilities Regulatory Authority or any corporate affiliate of any such company when the work performed by such affiliate is on behalf of a public service company, and in either case only if the work performed is in connection with the rendition of public utility service; (3) employees of any municipal corporation specially chartered by the state of Connecticut; (4) employees of any contractor while said contractor is performing work for or subject to inspection by any federal, state or municipal agency or corporation other than a municipal building department, or any public service company.