Bus plugs come in three basic configurations. A fusible switch uses fuses to prevent power overloads. The circuit breaker bus plug is similar in that it offers protection from overloads by stopping the flow of electricity--literally breaking the circuit as the name implies. Circuit breakers are found in most modern buildings, while fusible switch bus plugs may be in use for older homes, offices and historic landmarks.
Circuit breaker bus plugs close the circuit by "tripping". The circuit breaker switches off, and must be turned back on again to restore power. Unlike fusible switches, there are no fuses to replace after an electrical overload. This makes circuit breaker bus plugs more advantageous because no replacement purchases are needed. That doesn't mean a circuit breaker can't be damaged in some cases. Depending on the electrical fault, you may need to replace a circuit breaker bus plug. In some instances there may be partial power available to a home or office, in others you may have no electricity at all until the circuit breaker is replaced.