When rules are waived or modified safety shall be achieved in other ways such as using barricades, signs, guards, or other electrical protective equipment. Permission is given to use types of construction and methods of installation other than those specified in the NESC for experimentation to obtain information if done under qualified supervision. Where an existing installation is altered to meet the latest version of the NESC such an installation is considered to be in compliance with the latest edition and is not required to comply with a previous editions. The NESC rules in the current adopted edition are intended to be followed completely in new work under normal conditions. Exceptions are made for temporary, emergency, and experimental conditions.
Permission is given for the authority having jurisdiction to waive or modify any rule.
Most jurisdictions have appeal procedures where acceptance or rejection of any alleged violation or observed anomaly is evaluated on a case by case basis. For existing installations the current edition of the NESC is not retroactive. This is true of most construction codes. However, there are retroactive OSHA requirements that must always be taken into account when applying any rule from any code. OSHA has rules for new construction of transmission and distribution lines in Title 29, part 1926, Subpart V. Existing installations are required to conform to the NESC Code in effect at the time of the original construction.