It is not possible to state that an IP rating is equivalent to a NEMA type designation. An IP rating only considers protection against ingress of solid foreign objects and ingress of water. The NEMA types consider these, but also consider other items such as corrosions and construction details. For this reason, it is possible to assert that a NEMA type is equivalent to an IP rating, but it is not possible to state that an IP rating is equivalent to a NEMA type. The difference between IP65 and IP66 is the size of the nozzle diameter and the flow rate. If IP66 can be satisfied, then IP65 is also satisfied.