Anything contained in this Plumbing Code to the contrary notwithstanding, the installation of water softeners, washing machines, dryers, dishwashers, air conditioning equipment, ice makers, vending machines, coil cleaning machinery, garbage disposal units, refrigerators, humidifiers or other similar appliances as determined by the Plumbers Examining Board where such installation involves attachment to water lines, waste lines, drains or vent stacks, hereinafter called appliance installations, may be performed by a person holding a valid master or journeyman plumber's license; a valid building contractor's license; a valid specialty contractor registration; a valid plumbing contractor registration; or by a mercantile establishment which makes appliance installations through personnel trained in such installations and licensed in accordance with the provisions of Sections 1367.24 to 1367.26, inclusive, hereinafter called establishment.  However, appliance installations shall not include the attachment, extension or alteration of a trap; of a waste or drain lines on the outlet side of a trap; a vent stack; nor shall appliance installations include cutting into and inserting a fitting in a water line exceeding three fourth inch in diameter in a commercial building, three or more family dwelling or industrial building.