It shall be unlawful for a person to operate any steam boiler
or battery of boilers or engine in which more than 15 pounds of pressure
is maintained or more than 30 horsepower developed, including air
compressors of over 75 horsepower, or any power-developing unit used
to operate a refrigerating machine of over 50 tons' capacity
without first having obtained a license or certificate of fitness
therefor from the Commission. No such license or certificate of fitness
shall be issued unless the applicant has paid a permit fee therefor.
The provisions of this article shall not apply to persons operating
locomotives of incorporated railroad companies.
