Generally speaking, electricity and water are a bad mix. Precision electric motors should be keep clean and dry. But that's not practical in some applications, especially if the application is outdoors, like a cell phone tower, or involves processing fluids that can, on occasion escape, like in a brewery. Such applications are best suited for IP rated step motors. Since this is also an engineering blog, we strive for quantitative analysis. As luck would have it, there's a standard for everything, including ingress protection.