In order to renew a class A master electrician license, class B master electrician license, class A journeyman electrician license, or class B journeyman electrician license issued pursuant to this chapter, the licensee shall be required to complete eighteen contact hours of continuing education courses approved by the board during the three-year period for which a license is granted. The contact hours shall include a minimum of six contact hours studying the national electrical code described in section 103.6, and the remaining contact hours may include study of electrical circuit theory, blueprint reading, transformer and motor theory, electrical circuits and devices, control systems, programmable controllers, and microcomputers or any other study of electrical-related material that is approved by the board. Any additional hours studying the national electrical code shall be acceptable. For purposes of this section, “contact hour” means fifty minutes of classroom attendance at an approved course under a qualified instructor approved by the board.