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Circuit breaker refers to a switching device that can control the current of the machine under specified conditions (carrying and breaking the current under abnormal loop conditions). Circuit breakers can generally be divided into high-voltage circuit breakers and low-voltage circuit breakers, but the voltage division between the two is relatively vague. We usually call the high-voltage transformers above 3kV. Today, the editor will bring you a little knowledge of circuit breaker selection.

As a low-voltage circuit breaker for power distribution, there are mainly the following aspects when selecting:

First of all: it must meet the requirements of its type and technical parameters according to the workplace; second: after initially determining the type and specification of the circuit breaker, it is necessary to consider the coordination and cooperation between it and the upper and lower electrical appliances in terms of protection characteristics. Meet the requirements for selective protection; finally: check and select item by item.

The tripping characteristics of circuit breakers are divided into A, B, C, D, K, etc., and their meanings are as follows: Type A tripping characteristics: tripping current is (2～3) In, suitable for protecting semiconductor electronic circuits, with Measurement circuit of low-power power transformer, or system with long circuit and low short-circuit current; Type B tripping characteristics: tripping current is (3～5)In, suitable for household power distribution system, household appliances protection and personal safety protection ; C-type tripping characteristics: tripping current is (5～10)In, suitable for protecting power distribution lines, lighting circuits and motor circuits with higher on-current; D-type tripping characteristics: tripping current is (10) ～20)In, suitable for protecting equipment with high inrush current, such as transformers, solenoid valves, etc.; K-type tripping characteristics: 1.2 times the thermal tripping current and 8-14 times the magnetic tripping operating range, suitable for It protects the motor circuit equipment and has high resistance to impact current.

The air switch is used as a main power protection switch or branch line protection switch in the household power supply. When a short circuit or overload occurs in residential circuits or household appliances, it can automatically trip and cut off the power supply, thereby effectively protecting these equipment from damage or preventing accidents from expanding; households generally use two-pole (ie 2P) air switches for main power protection. Single pole (1P) is used for branch protection; if the rated current of the air switch is selected too small, the air switch is likely to trip frequently and cause unnecessary power outages. If the selection is too large, the expected protection effect will not be achieved, so home improvement For air switches, it is important to correctly select the rated capacity and current. General small air switch specifications are mainly based on the rated current area of 6A, 10A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A, etc.; then how does the average family choose or check the total value of the total load current?

1. First calculate the value of each branch current

①Pure resistive loads, such as light bulbs, electric heaters, etc., can be obtained by directly dividing the indicated power by the voltage, the formula I=power/220v; for example, for a 20w bulb, the branch current I=20W/220=0.09A. Electric fans, electric irons, electric blankets, electric water heaters, electric heaters, rice cookers, electric frying pans, vacuum cleaners, air conditioners, etc. are resistive loads.

②Inductive loads, such as fluorescent lights, televisions, washing machines, etc. The calculation is slightly complicated, and the power consumption should be considered, and the specific calculation should also consider the power factor. To facilitate the estimation, the author gives a simple calculation method, that is, the general inductive load. It is sufficient to indicate that the calculated power of the load is doubled. For example, indicate that the branch current of a 20W fluorescent lamp is I=20W/220v=0.09A, which is doubled to 0.09A*2=0.18A (than the exact calculated value of 0.15A , 0.03A more)

2. The total load current is the sum of each branch current

Knowing the branch current and the total current, you can choose the branch air switch and the main brake air switch, the main fuse, the total meter and the specifications of the branch wires, or check whether the specifications of the designed electrical components meet the safety requirements;

3. To ensure safety and reliability

The rated working current of electrical components should generally be greater than 2 times the required maximum load current;

In addition, when designing and selecting electrical components, it is necessary to consider the possibility of future increase in electrical load, leaving a margin for future demand;

The circuit breaker selection is difficult, simple and not easy. Only by mastering certain skills can you make better choices and purchases. Hope the above knowledge can be helpful to everyone.