An electrician is responsible for running power from a main distribution panel (MDP) to a large HVAC unit located on the roof of a commercial building. The circuit will be 600 V, 3-phase, 100 A. The run involves a long vertical rise up the exterior wall, exposed to direct sunlight, then across the rooftop. Considering mechanical protection, environmental conditions, and proper support, which wiring method would be the most appropriate and compliant with the CEC?

Question: An electrician is responsible for running power from a main distribution panel (MDP) to a large HVAC unit located on the roof of a commercial building. The circuit will be 600 V, 3-phase, 100 A. The run involves a long vertical rise up the exterior wall, exposed to direct sunlight, then across the rooftop. Considering mechanical protection, environmental conditions, and proper support, which wiring method would be the most appropriate and compliant with the CEC?

Answer options:

• NMD90 cable in Schedule 40 PVC conduit
• Armoured cable (AC90) secured to the exterior wall and roof via trapeze hangers ✅ Rigid Metal Conduit (RMC) with appropriate expansion fittings and supports
• Liquidtight Flexible Non-metallic Conduit (LFNC) in a cable tray system

Correct answer: Rigid Metal Conduit (RMC) with appropriate expansion fittings and supports

Explanation: Rigid Metal Conduit (RMC) is highly recommended for exposed outdoor installations, especially vertical rises, as it provides excellent mechanical protection, withstands UV degradation, and can properly be supported. Expansion fittings are crucial for long runs exposed to temperature extremes. NMD90 is not for outdoor use. AC90 is generally not suitable for exposed exterior runs. LFNC is flexible and typically used for short connections, not for long primary runs, and a cable tray alone does not provide the same level of mechanical protection.