It shall be unlawful for any person controlling such wiring to allow any electrical current for lighting or other purposes to be turned on in any building without first having had an inspection of the wiring made and a certificate of such inspection issued by the inspector. Such inspection shall be made by the city electrician, who shall certify it to the inspector in writing, who may, thereupon, issue the certificate. No alterations shall be made in the wiring of any building unless a certificate shall be obtained from the inspector approving them.