With regard to the application of four pole circuit breakers, there are no hard requirements for the use of national standards or regulations in China. Although the design specifications of regional four pole appliances (circuit breakers) have been issued, the debate on whether to install or not to install four pole appliances is still ongoing. The use of four pole appliances in some areas has been in a swarm in recent years, and various circuit breaker manufacturers have designed them one after another, Manufacture various types of four pole circuit breakers and put them on the market. The author agrees that whether to use or not should be based on whether it can ensure the reliability and safety of power supply. Therefore, it is generally as follows:

(1) TN-C system. In TN-C system, the N line and the protection line PE are combined into one (pen line). Considering safety, it is not allowed to disconnect the pen line at any time, so the four pole circuit breaker is absolutely prohibited;

(2) TT system, TN-C-S system and TN-S system can use four pole circuit breaker to ensure the safety of maintainers during maintenance. However, for TN-C-S and TN-S systems, the N pole of the circuit breaker can only be connected with n wire, not pen or PE wire;

(3) In places where dual power switching is installed, since all neutral lines (n lines) in the system are connected, in order to ensure the maintenance safety of the switched power switch (circuit breaker), four pole circuit breaker must be used;

(4) For the single-phase main switch entering the residence, a two pole circuit breaker with N pole should be selected (used as an isolator during maintenance);

(5) For the residual current protector (leakage circuit breaker) used in 380 / 220V system, the neutral line must pass through the zero sequence current transformer (iron core) of the protector to prevent the passage of no neutral line and the misoperation of 220V load due to leakage current. At this time, four pole or two pole residual current protector with neutral line shall be selected.