Understanding the IP Rating System Like most suppliers Mertech's enclosures  conform to an  international system  which assigns an Ingress Protection or IP protection rating. A summary of the IP  system is given below. The IP system is relative and rational always two letters  (IP) followed by two digits. The first digit indicates the enclosure's degree of  protection against solid objects while the second digit indicates a degree of  protection against liquids.  MerTower SWITCHGEAR