Which assembly type must be connected to metallic piping for bonding purposes according to NEC guidelines?

The correct assembly type that must be connected to metallic piping for bonding purposes according to NEC guidelines is drain fittings. This requirement is primarily based on safety concerns, as drain fittings are part of the grounding system that helps prevent electrical shocks in areas where water may accumulate.

Bonding ensures that all electrically conductive parts of the pool or spa equipment, including drain fittings, are at the same electrical potential. This reduces the risk of accidental electric shock in wet environments, which is critical for ensuring the safety of individuals using these installations. By connecting drain fittings to metallic piping, a continuous path is created for electrical currents to flow safely to the ground, enhancing the overall electrical safety of the installation.

In contrast, the other assembly types mentioned do not have the same explicit NEC bonding requirements as drain fittings. They may be involved in different functions or forms of installation, but they do not directly link to the bonding provisions in the NEC as outlined for drain fittings.