"This application guide covers molded case circuit breakers and molded case switches@ single-pole and multi-pole@ fused and unfused@ as well as accessories used with them. These circuit breakers and switches are assembled as integral units in supporting housings of insulating material and have rated voltages up to and including 1000 V@ 50/60Hz@ AC or AC/DC@ and have rated interrupting current ratings of 5000 amperes or more. Note: Consult the manufacturer for dc-only or 400 Hz circuit breakers. This application guide addresses electrical systems with nominal ratings of 600 volts and below ac and dc@ which represent the preponderance of the general use application. Wherever the term circuit breaker or breaker is used in this publication@ it is understood to mean molded case circuit breaker. Wherever the term switch is used in this publication@ it is understood to mean molded case switch. Wherever the abbreviation UL appears@ it shall be understood to mean Underwriters Laboratories@ Inc. Wherever the abbreviation NEC or ""Code"" appear@ they shall be understood to mean the National Electrical Code. ""NEC"" and ""National Electrical Code"" are registered trademarks of the National Fire Protection Association. With the exception of the definitions@ Appendix A@ and where mandatory requirements are indicated by such language as ""shall@"" ""must@"" and ""such@"" this document has been classified as Authorized Engineering Information."