As fuses and circuit breakers show insufficient surge current withstand capability when used in conjunction with SPD, it is necessary to improve the surge current withstand capability. Analyzing the influence of circuit breakers with different rated currents on the breaking capacity of the SSD power frequency short-circuit circuit, to summarize the selection points and coordination suggestions of different components.

  With the increasingly stringent requirements of modern electronic equipment for lightning protection, the installation of surge protectors to suppress the surge and transient overvoltage on the line and discharge the overcurrent on the line has become one of the important links of modern lightning protection technology. As we all know, the important component of the surge protector is the varistor (MOV), and the varistor has leakage current, which may cause short-circuit degradation during long-term use, which brings security risks to the system. This requires SPDs to be used in series with overcurrent protection devices, which are listed in Appendix J of the national standard GB50057-2010 "Code for Lightning Protection Design of Buildings" and GB/T18802.12-2014/IEC61643-12: 2008 "Electricity of Low-Voltage Distribution Systems" In Appendix K of "Surge Protector (SPD) Part 12: Guidelines for Selection and Use", it is stipulated that an overcurrent protector should be installed in series on the side of the surge protector close to the phase line, usually called SPD backup protection device.

Civil building electrical design standard: GB51348-2019, which puts forward specific requirements for the use of backup protection devices:

1. Break the expected short-circuit current of the SPD installation circuit;

2. To withstand the surge current passing through the SPD without disconnection

3. Break the power frequency current that cannot be cut off by the SPD's built-in thermal protection.

  Jinli backup protector can be a good SPD qualified backup protector.