Introduction  In the DC power supply system, the cable section is usually selected according to the long-term allowable current-carrying capacity of the cable and the allowable voltage drop of the circuit. However, in actual projects, a larger rated current of the circuit breaker may be selected due to stage difference coordination. In this case, the circuit breaker will not act and will burn the cable when the cable is overloaded or short circuited. On one hand, this paper illustrates this problem with project examples. On the other hand, it tries to find a simple relation between cable and circuit breaker to facilitate engineering design.

  Method  On one hand, the selection of cable and the coordination method of DC circuit breaker were briefly introduced through practical examples; On the other hand, the coordination between cable and circuit breaker was analyzed by means of data fitting and curve analysis.

  Result  A set of engineering practical relations between cable section and rated current of circuit breaker are obtained.

  Conclusion  The engineering practical relations between cable section and rated current of circuit breaker have a wide range of applications, providing reference for cable design of DC system in future projects.