Section 45. Examinations; conducting business without certificate prohibited

A  person  desiring  or  intending  to  conduct  the  trade,
  business  or calling of a plumber or of plumbing in a city of this state
  as employing or master plumber,  shall  be  required  to  submit  to  an
  examination before such examining board of plumbers as to his experience
  and qualifications for such trade, business or calling, and it shall not
  be  lawful in any city of this state for a person to conduct such trade,
  business or calling, unless he shall have first obtained  a  certificate
  of  competency  from  such  board  of  the  city in which he conducts or
  proposes to conduct such business.