Every person who shall, without the written permission of the owner, lessee, or person or corporation operating any electrical transmission line, distributing line or system, climb upon any pole, tower or other structure which is a part of such line or system and is supporting or is designed to support a wire or wires, cable or cables, for the transmission or distribution of electric energy, shall be deemed guilty of a misdemeanor; provided, that nothing herein shall apply to employees of either privately or publicly owned public utilities engaged in the performance of their duties.