As used in this act:
a. "Commissioner" means the Commissioner of Labor or any of his authorized representatives.
b. "High-voltage lines" means electrical conductors installed above ground and having a voltage differential in excess of 750 volts between any pair of conductors or between any conductor and ground. In the case of alternating current, the voltage shall be measured in R.M.S. value. This definition shall not include approved armored cable used to supply power to portable equipment and insulated power cables enclosed in approved metallic raceways.