110.30–110.41 Over 1000 V ac, 1500 V dc
These sections cover controlled access, working space and guarding, entrance and egress, separation from lower-voltage equipment, warning signs and illumination, and conductor, termination, torque and testing requirements. Working-space depth increases as voltage rises. Higher voltage means more separation, more guarding and tighter access control.
110.31 Enclosures
Vaults, rooms, closets, walls, screens or fences restrict access and protect unqualified persons from exposed energized parts.
110.32–110.34 Work space and access
Enough space is kept for safe operation and maintenance. Large equipment can trigger additional entrance, egress, guarding and personnel-door requirements.
110.51–110.59 Tunnel installations
Tunnels over 1000 V ac or 1500 V dc add physical protection, conductor requirements, bonding and grounding, equipment protection, guarding of energized parts, ventilation controls, disconnecting means and enclosures.
110.70–110.79 Manholes and personnel-entry enclosures
These spaces are built for people as well as cable: structural strength, cabling and equipment work space, conductor installation, openings and covers, access to vaults and tunnels, ventilation, guarding and fixed ladders.
Why it matters
At these voltages the electrical-room layout becomes an architectural, structural and MEP problem at once. Poor layouts produce short working clearances, blocked egress, unsafe proximity between equipment, access conflicts and equipment that cannot be maintained.
Field tip
For vaults, tunnels and manholes, review the human path, not just the equipment. Can someone enter safely, work safely and leave quickly? Is ventilation adequate? Can the equipment be maintained in place? That is where constructability and electrical safety meet. Next: NEC 2026 Article 120 Load Calculations Kickoff.
The takeaway
110.30–110.41 → separation, guarding, access and testing over 1000 V ac / 1500 V dc.
110.51–110.59 → tunnel protection and environmental coordination.
110.70–110.79 → access, work space, ventilation and structure planned for people.
That completes the 10-part Article 110 series.
Code basis
NEC 2026 Article 110 Parts III–V education from the owner-provided Daily Code Talk. Utility-owned equipment and vaults follow the serving utility’s requirements. Confirm the locally adopted NEC edition and amendments.