Understanding General Requirements of the NEC, Part 18
Article 110 provides general requirements for all installations. Part IV provides the requirements for tunnel installation over 1000VAC, 1500VDC.
Conductors and cables in tunnels must be above the tunnel floor [Sec. 110.51(B)]. They must be placed and guarded to protect them from physical damage, and the same applies to transformers, switches, and other electrical equipment placed underground.
If the conductors are high voltage, they must be installed in metal raceways Type MC cable, or other approved multiconductor cable [Sec. 110.53].
You have to bond all non-current carrying metal parts of electrical equipment and all metal raceways and cable sheaths to all metal pipes and rails at the portal and at intervals not exceeding 1000 ft throughout the tunnel [Sec. 110.54].
Electrical controls for the ventilation system must be arranged such that the airflow can be reversed [Sec. 110.57].
Each transformer and motor requires a disconnecting means within sight of it. That disconnecting means must simultaneously open all ungrounded conductors [Sec. 110.58].
Enclosures in tunnels must be dripproof, weatherproof, or submersible, depending on the particulars of the environment. Don’t use switch or contactor enclosures as junction boxes or raceways, unless the enclosure complies with Sec. 312.11 (which provides fairly stringent requirements) [Sec. 110.59].
About the Author
Mark Lamendola
Mark is an expert in maintenance management, having racked up an impressive track record during his time working in the field. He also has extensive knowledge of, and practical expertise with, the National Electrical Code (NEC). Through his consulting business, he provides articles and training materials on electrical topics, specializing in making difficult subjects easy to understand and focusing on the practical aspects of electrical work.
Prior to starting his own business, Mark served as the Technical Editor on EC&M for six years, worked three years in nuclear maintenance, six years as a contract project engineer/project manager, three years as a systems engineer, and three years in plant maintenance management.
Mark earned an AAS degree from Rock Valley College, a BSEET from Columbia Pacific University, and an MBA from Lake Erie College. He’s also completed several related certifications over the years and even was formerly licensed as a Master Electrician. He is a Senior Member of the IEEE and past Chairman of the Kansas City Chapters of both the IEEE and the IEEE Computer Society. Mark also served as the program director for, a board member of, and webmaster of, the Midwest Chapter of the 7x24 Exchange. He has also held memberships with the following organizations: NETA, NFPA, International Association of Webmasters, and Institute of Certified Professional Managers.