Leakage circuit breakers are generally divided into two poles, three poles, and four poles, which are used in different circuits. Only the correct selection and use can play its due role, so pay attention to the following five points when choosing a leakage circuit breaker:
1) The rated current of the overload release ≥ the maximum load current of the line;
2) The limit making and breaking capacity of the circuit breaker is greater than or equal to the maximum short-circuit current of the circuit;
3) The leakage current to be protected by the circuit should be less than the specified leakage protection current of the circuit breaker;
4) The normal working voltage and current of the line equipment ≤ the rated voltage and current of the circuit breaker;
5) It has a short breaking reaction time, which can protect the circuit and equipment.
Sometimes it is difficult to judge whether to choose a four-pole circuit breaker in the application. The principles to be followed for whether to choose a four-pole circuit breaker are proposed here. In the following cases, a four-pole circuit breaker should be selected:
1) According to the provisions of IEC465.1.5, the conversion circuit breaker between the normal power supply and the standby generator; 2) The dual power conversion circuit breaker with leakage protection should adopt a four-pole circuit breaker. Two upper-level circuit breakers are equipped with leakage protection, and the lower-level power conversion circuit breaker; 3) Power switch circuit breaker between two different grounding systems; 4) Power incoming circuit breaker of the TT system; 5) When there is a medium in the IT system The circuit breaker used when the neutral wire is drawn out.
In the following situations, it is generally not necessary to use a four-pole circuit breaker or the use of a four-pole circuit breaker is prohibited:
1) TN-S and TN-C-S systems generally do not need to be equipped with four-pole circuit breakers;
2) Four-pole circuit breakers are strictly prohibited in the TN-C system.