A working group representing the Petroleum and Chenzical Industry Conmittee (PCIC) and the Low-Voltage Protection Subcommittee, including both users and electrical equipment manufacturers is preparing a guide to give users information f;,r the correct selection and application of molded-case circuit breakers @fCCBs) under short-circuit conditions. This puper is intended to he a tutorial presentation which will attempt to resolve issues that have been raised in a number qf recent IEEE papers. This is phase one of a series qf papers and tutorials relating to the selection and upplication of MC'CBs.