The provisions of this chapter do not apply to licensed mechanical contractors performing emergency repair work on existing fire protection sprinkler systems or existing water spray systems or existing water foam systems where the labor cost of the work does not exceed one thousand dollars or to persons engaged in the repair, alteration, maintenance, or inspection of a fire protection sprinkler system or water spray system or water foam system on their own property or that of their normal employer. Plumbing contractors holding a Group 2 or 3 plumbing contractor license are not required to be licensed under this chapter to install standpipe systems, including hose connections, hose cabinets, and related branch lines, provided that they do not supply automatic fire protection sprinklers. A utility contractor holding a Group 2 or 3 utility contractor license is not required to be licensed under this chapter to install underground water mains, hydrant mains, and fire hydrants to the point of the connection to the underground fire protection sprinkler system mains.