What type of motors shall not be bonded in hydromassage bathtubs?

Double-insulated motors are specifically designed in a way that they have an extra layer of insulation between the electrical components and the motor housing. This construction aids in providing enhanced safety by preventing electrical shock in wet environments, which is critical in spaces like hydromassage bathtubs.

The NEC recognizes the unique design of double-insulated motors, allowing them not to require bonding because their safety relies on their inherent design rather than a ground connection. This is an important aspect when it comes to compliance with safety regulations in wet areas, as bonding other types of motors could create unnecessary paths for fault current or introduce safety hazards.

In contrast, other types of motors, such as standard motors, high-efficiency motors, or low-voltage motors, can often require bonding to ensure proper grounding and safety in potential fault scenarios. Therefore, double-insulated motors stand out as the exception in this context, validating the chosen answer.