IEC60050-605-02-40 and 41

The bus coupler circuit breaker is coupling two bus section and make one common bus if either one source of supply available or two supply syncronized supply available to share the heavy load. if bus coupler circuit breaker open two source will feed load separately.

The difference between two is switched busbar circuit breaker will be eaither as source or load breaker in "T" connection

Bus coupler connecting two end to end bus

switched cb connecting in T coonection

it is used in case more than one source of supply.