These are motors used in the food processing or drug industry, thus they are subject to frequent washdowns, sometimes with high-pressure water or chemical mixtures. These motors are very well sealed; even a small amount of water can damage a bearing. Actually, these motors are built knowing that the inside and outside of a motor needs equal protection. The conduit box is well-gasketed, not to mention the stuffing box (gland) where the shaft exits the motor enclosure. For the eventual moisture that gets trapped inside, the rotor and shaft are epoxy-coated. The stator coils are also dipped in moisture-proof varnish which is then baked.
The enclosure must not have sharp bends or folds, as matter like flour can build-up in the nooks and crannies. Normal paint is not to be used – hits can generate paint chips that can get into the food. Also, chipped paint is a good place for bacterial growth (they like the warmth of the motor and are protected from water jets). Because of this, special coatings must be used: electrostatically applied epoxy which is then baked in a special oven. This makes it less prone to chipping and offers good corrosion protection.
White is recommended as a color in order to spot dirt easily.
For some applications, the more expensive stainless steel is the preferred material.