In tunnel installations, which type may be used for high-voltage conductors?

• A. Metal conduit or other metal raceway, Type MC cable, or other approved multiconductor cable
• B. Only nonmetallic sheath cable
• C. Bare wires without protection
• D. Flexible cords

Answer: (A)

In tunnel installations, high-voltage conductors must be protected by a listed raceway or cable assembly that provides solid mechanical protection and environmental resistance. Metal conduit or other metal raceways, Type MC cable, and other approved multiconductor cables are designed for rugged, fixed installations and can withstand the moisture, vibration, and potential physical damage common in tunnels. They also offer a proper enclosure and grounding path for safe operation.

Nonmetallic sheath cable isn’t suitable for this environment because it lacks the necessary protection against moisture and physical damage. Bare wires have no insulation or protection, creating shock and short-circuit hazards. Flexible cords are meant for temporary or movable use and not for permanent high-voltage feeders in fixed tunnel installations.