Ingress Protection ratings are defined in international standard EN 60529. They are used to define levels of sealing effectiveness of electrical enclosures against intrusion from foreign bodies (tools, dirt, etc.) and moisture.

As a guideline, IP ratings of between 44 and 65 may be used for indoor and general outdoor use. An IP rating of 67 is the highest achievable level, indicating that the device may be submerged permanently in water at a depth of up to 13 feet. Anything lower than IP44 should only be for use indoors, however. IP66, on the other hand, is typically used for heavy-duty industrial and waterproof electrical enclosures.

To make the Mullion reader range compliant to IP66, a few hardware changes were undertaken, marked on the packaging label with hardware rev. 08. Customers will notice a small opening at the bottom of the metal housing alongside a new rubber gasket added to the packaging.