What must all metal housings and service enclosures be according to the connection requirements on the supply side of the service disconnecting means?

All metal housings and service enclosures must be grounded and bonded according to the connection requirements on the supply side of the service disconnecting means. This requirement ensures that any fault current has a clear, low-resistance path to the ground, which helps to prevent electric shock and other hazards. Grounding provides a safe path for excess electricity to dissipate, reducing the risk of electrical fires and equipment damage. Bonding ensures that all conductive parts are connected together, minimizing potential differences in voltage that could be dangerous to individuals or equipment. These practices are critical for ensuring the safety and reliability of electrical installations as outlined in the National Electrical Code (NEC).

The other options, while potentially relevant in certain contexts, do not meet the specific requirements for service enclosures and housings on the supply side of the service disconnecting means as detailed in the NEC. For example, double insulation may enhance safety in certain situations, but it does not replace the need for effective grounding and bonding in metallic structures. Similarly, while water-resistance can be important for certain installations, it does not address the fundamental safety mechanisms necessary for electrical systems, nor does the use of PVC insulation provide the required protection against faults in metal enclosures.