Listing or labeling of materials, devices and appliances by the Underwriters’ Laboratory, Inc., or other testing laboratory approved by the chief electrical inspector as complying with standards on file with the United States Bureau of Standards may be accepted by the chief electrical inspector as prima facie evidence of the conformity of such materials, devices and appliances with corresponding provisions of the code of standards of said city or of corresponding rules and regulations adopted under this chapter. (Prior code § 7.22.060)