Part 3 — Safety Rules for the Installation and Maintenance of Underground Electric Supply and Communication Lines of the National Electrical Safety Code establishes safety requirements for underground electric supply and communication systems, including cables, conduits, ducts, vaults, manholes and associated equipment.
Its principal concerns are location, burial, mechanical protection, separation and accessibility. The rules address underground structures, direct-buried cables, supply and communication cables occupying common spaces, crossings with other utilities and protection against foreseeable excavation or physical damage. Part 3 also covers grounding and bonding, cable identification, work space and provisions intended to make underground systems safe for both workers and the public.
Particular attention is given to manholes and vaults, including access, drainage, ventilation where required and arrangements that reduce hazards from energized equipment, fire or accumulated gases.
For universities and other large educational settlements, Part 3 governs much of the infrastructure that is seldom visible: campus primary distribution, duct banks, utility tunnels and vaults, roadway crossings, telecommunications pathways and transitions between overhead and underground lines.
