Md. Code, Bus. Reg. § 9A-103

This title does not limit the right of: (1) an individual owner of a single-family dwelling while that owner is practicing heating, ventilation, air-conditioning, or refrigeration services on or within a building or structure owned by the individual; (2) an individual who is building a single-family dwelling in which that individual will reside while practicing heating, ventilation, air-conditioning, or refrigeration services on or within that dwelling; (3) an employee of a public utility company regulated by the Public Service Commission, when engaged in: (i) the development, construction, maintenance, or repair of electric or gas facilities located in the State; or (ii) the construction, maintenance, or repair of electric or gas appliances in the service area of the public utility; (4) subject to § 9A-403(a) of this title, an employee of the United States government, the State government, a local government, or an independent agency while that employee is practicing heating, ventilation, air-conditioning, or refrigeration services on or within buildings or structures owned or solely occupied by the United States government, the State government, a local government, or an independent agency; (5) an individual employed in the installation, maintenance, alteration, repair, or replacement of self-contained appliances requiring not more than 225 volts or 25 amperes of electrical current; (6) an individual possessing a master electrician's license issued by the State or any county, when engaged in the installation, alteration, service, repair, or replacement of individually controlled electric resistance heat; (7) an individual possessing a master plumber's license issued by the State, Baltimore County, or the Washington Suburban Sanitary Commission when providing heating, ventilation, air-conditioning, or refrigeration services on hydronic heating systems; (8) an individual possessing a license to practice engineering when providing heating, ventilation, air-conditioning, or refrigeration services in connection with the practice of engineering; (9) an individual who installs, alters, remodels, maintains, or repairs oil burners exclusively while employed by a supplier of home heating fuel; or (10) an individual regularly employed by the owner of property, or the owner's agent, to engage in maintenance and repair work.