A motor controller enclosure that is subject to occasional prolonged submersion shall be type ___.

A motor controller enclosure that is subject to occasional prolonged submersion must be classified as type 6P. Type 6P enclosures are designed to provide a high level of protection against water and can withstand occasional submersion in water. This makes them particularly suitable for environments where there may be exposure to water for extended periods, ensuring that the internal components of the motor controller remain safe and functional.

In contrast, other enclosure types do not offer the same level of protection against prolonged submersion. Type 3S, for instance, is designed for indoor and outdoor use but does not provide the same level of water resistance as type 6P. Type 12 enclosures offer protection against dust and moisture but are not rated for water submersion. Type 4X is designed to protect against corrosion and water but does not specify submersion capability to the extent of type 6P. Thus, type 6P is the appropriate choice for applications requiring protection during occasional prolonged exposure to water.