Interplay of energies in circuit breaker and fuse combination

The authors review some of the contemporary operating principles of molded case circuit breakers and fuses. Emphasis is placed on energy levels. An analysis of cause and effect shows why analytical selection of fuses for circuit breaker protection may yield unsafe combinations. It is demonstrated that evolving product technology is forcing a change in application techniques. The authors agree that, at present, suitable fuse-circuit breaker combinations can only be determined by testing the two in series if the breaker has a repulsion contact design. Circuit breakers which are not of the repulsion contact design may be adequately protected by fuses chosen by analytical selection methods. It is concluded that the application engineer selecting the fuse-breaker combination method should consult the circuit breaker manufacturer to confirm the validity of the selection.<>