This new twelfth edition of ANSI/UL 50 is the result of the harmonization effort to develop a tri-national standard covering requirements for enclosures for electrical equipment. The twelfth edition of UL 50 contains the non-environmental construction, performance, and marking requirements for enclosures. The requirements for enclosure construction, performance, and markings based on environmental type rating designations have been organized into a new standard, UL 50E, Standard for Enclosures for Electrical Equipment, Environmental Considerations.