Popular version explanation
Model of air switch:
C65/D65 D stands for power, C stands for lighting.
1. At present, DZ series air switches (miniature circuit breakers with leakage protection) are used in households.
The following models/specifications are common: C16, C25, C32, C40, C60, C80, C100, C120 and other specifications, where C represents the tripping current, that is, the take-off current, for example, C32 represents the take-off current is 32 amps, and a 6500W water heater is generally installed To use C32, to install 7500W, 8500W water heaters to use C40 air switch.
2. The common models in the industry are: DW and DZ types for power circuits;
Points 20, 32, 50, 63, 80, 100, 125, 160, 250, 400, 600, 800, 1000 (unit A).
The rated current of the open circuit is several amps to hundreds of amps, such as 10 amps and 600 amps, but the maximum current of the ordinary DZ47-63 series is 63 amps, divided into 5 10 16 (15) 20 25 32 (30) 40 50 60 (63).
Main points:
1. The rated voltage of the air switch is greater than or equal to the rated voltage of the line;
2. The rated current of the air switch and the rated current of the overcurrent release are greater than or equal to the calculated load current of the line.
example:
DZ47-60A C25:
DZ47——series of miniature circuit breakers (there are many series, which are basically named by the manufacturer)
LE——with leakage tripping function
60 - the frame rating is 60A
C——Instantaneous tripping overcurrent multiple according to the clear category, such as 5~7 or 7~10 times, D is 10~14 times for the power type
The air switch is used to protect the wires and prevent fires, so it should be selected according to the size of the wires rather than the power of the electrical appliances.
1. If the air switch is too large, there is no need to protect the wires. When the wires are overloaded, the air switch will not jump, which will bring hidden dangers to family safety.
2. So you should check the size of the wire first, if the wire allows a larger air switch, you can change it to a larger air switch.
1.5 square wire with C10 switch;
2.5 square wire with C16 or 20 switch;
4 square wires with C25 switch;
6 square lines with C32 switch.
3. Based on what basis to choose the main and receiving air switch (3P or 4P) of the low-voltage cabinet, look at the selection of the four-pole circuit breaker
In the following situations, it is necessary to use a four-pole circuit breaker:
1. A four-pole circuit breaker must be selected for a system with dual power switching requirements to meet the isolation requirements for maintenance, testing and overhaul of the entire system;
2. The single-phase main switch of each residential household should use a two-pole switch with N poles (four-pole circuit breakers can be used);
3. The residual current action protector (leakage switch) must ensure that all live wires in the protected circuit are disconnected. Therefore, for circuits with residual current action protection requirements, N poles (such as four poles) should be selected. Leakage circuit breakers.
It is to consider that you will use air conditioners in the future, so the total space switch should be 32. If you have more air conditioners in the future, you may need to use 40-60 space switches. If you have 4 floors, you can actually use the lighting and lighting of each floor Sockets use 15A, and if there are large electrical appliances such as air conditioners, a 15A air switch should be used for wiring. Especially in the kitchen, where there will be a lot of electrical appliances in the future, a separate air switch should be set up. This should be considered farther away. , leaving room for increasing power in the future. The public account "Mechanical Engineering Literature", a gas station for engineers!
1. The total capacity of all electrical appliances is 5000W, and the load is not heavy. Just use [32A/2P circuit breaker + leakage tripping accessories]. If the [requirement factor] is considered, the 25A specification is also acceptable.
2. Calculation formula: Ijs=Kx*P/U/cosφ
in:
Ijs - calculate current
Kx——demand coefficient; household electricity Kx between 0.5-0.7 is sufficient
P - installation capacity; all electrical appliances (sockets are also included, and each 100W is estimated)
cosφ——power factor; civil electrical lines are estimated at 0.85-0.9
3. After getting the calculated current value, choose a circuit breaker that can be set with a size of 1 or 2, but pay attention to the matching between the circuit breaker and the line it protects (point out the line circuit)
16A - the corresponding line is BV-2.5;
20, 25A - the corresponding line is BV-4;
32A - the corresponding line is BV-6;
40A——The corresponding line is BV-10 (generally the specification of residential incoming line, corresponding to 40A electric meter).
4. Air switch, also known as automatic switch, low-voltage circuit breaker; the principle is to automatically cut off the circuit when the working current exceeds the rated current, short circuit, loss of voltage, etc.
DZ47-60A C20 air switch, this is the rated current standard of micro (small) circuit breakers, the English word indicates the action multiple of magnetic tripping (short circuit protection), C is generally used for ordinary power distribution (5-10 times) , Another common type is D type, which is used for electrical appliances with large starting current (such as motors) (10-14 times). 20A represents the rated current, but it should be noted that this current is the setting value when the ambient temperature is 40 degrees Celsius. In actual use, please refer to the derating curve provided by the manufacturer.
5. Selection of household circuit breaker air switch
1. Circuit breaker, the full name of automatic air circuit breaker, also known as air switch, is a commonly used low-voltage protection device, which can realize functions such as short circuit and overload.
2. The circuit breaker is used as a main power protection switch or branch line protection switch in household power supply. When short-circuit or overload occurs in residential lines or household appliances, it can automatically trip and cut off the power supply, thereby effectively protecting these devices from damage or preventing accidents from expanding;
3. Households generally use two-pole (2P) circuit breakers for general power protection, and single-pole (1P) for branch protection;
4. If the rated current of the circuit breaker is selected too small, the circuit breaker will trip frequently and cause unnecessary power outages. If the rated current of the circuit breaker is selected too large, the expected protection effect will not be achieved. Therefore, install a circuit breaker and correctly select the rated capacity The amount of current is important.
5. The specifications of general miniature circuit breakers are mainly distinguished by rated current 6A, 10A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A, etc.;
So how do ordinary families 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.
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, electric rice cookers, electric frying pans, vacuum cleaners, air conditioners, etc. are resistive loads;
②Inductive loads, such as fluorescent lamps, TV sets, washing machines, etc., are slightly more complicated to calculate, and power consumption must be considered, and power factor should also be considered in specific calculations. For ease of estimation, the author gives a simple calculation method, that is, general inductive loads The power calculated by indicating the load can be doubled. For example, the branch current I=20W/220v=0.09A of the fluorescent lamp marked 20W, doubled to 0.09A*2=0.18A (compared with the accurate calculation value of 0.15A , more than 0.03A); fluorescent lamps, refrigerators, TVs, etc. are classified as perceptual.
2. The total load current is the sum of the branch currents; knowing the branch current and the total current, you can select the branch circuit breaker and the main gate circuit breaker, the main fuse, the main electric meter and the specifications of the branch wires, or check the designed Whether the specifications of these electrical components meet the safety requirements; the public account "Mechanical Engineering Wenhui", a gas station for engineers!
In addition, in order to ensure safety and reliability, the rated operating current of electrical components should generally be greater than 2 times the required maximum load current; in addition, when designing and selecting electrical components, the possibility of increasing electrical loads in the future should also be taken into account, for future Requirements leave a margin;
1. General current carrying capacity of copper conductors
The safe current carrying capacity of the wire is determined according to the maximum allowable core temperature, cooling conditions, and laying conditions. Generally, the safe current carrying capacity of copper wire is 5~8A/mm², and that of aluminum wire is 3~5A/mm².
like:
The recommended safe current carrying capacity of 2.5 mm² BVV copper wire is 2.5×8A/mm²=20A
The recommended safe current carrying capacity of 4 mm² BVV copper wire is 4×8A/mm²=32A
Second, calculate the cross-sectional area of copper wire
Calculate the upper and lower ranges of the cross-sectional area S of the selected copper wire by using the recommended value of the safe current carrying capacity of the copper wire 5~8A/mm²
S=[ I / (5~8)]=0.125 I ~0.2 I (mm²)
S - cross-sectional area of copper wire (mm²)
I - load current (A)
3. Power calculation
General loads (which can also be electrical appliances, such as lighting, refrigerators, etc.) are divided into two types, one is resistive load and the other is inductive load.
Calculation formula for resistive load: P=UI
The calculation formula for the fluorescent lamp load: P=UIcosф, where the power factor of the fluorescent lamp load cosф=0.5. Different inductive loads have different power factors, and the power factor cosф can be taken as 0.8 when calculating household appliances in a unified manner.
That is to say, if the total power of all electrical appliances in a family is 6000 watts, the maximum current is I=P/Ucosф=6000/220*0.8=34(A).
However, under normal circumstances, it is impossible to use the electrical appliances at home at the same time, so a common factor is added, and the common factor is generally 0.5. Therefore, the above calculation should be rewritten as I=P*Common Coefficient/Ucosф=6000*0.5/220*0.8=17(A) In other words, the total current value of this family is 17A. The air switch of the main gate cannot use 16A, and the calculation of electric power greater than 17A should be used. Generally speaking, the power is the power consumption of electrical appliances, and to be precise, it is the power consumption of electrical equipment per unit time. For household single-phase electrical equipment, the formula for power calculation is simple:
P=U×I×COSφP
Power, refers to the active power unit: watts (W)
1kW=1000W(1kW=1000W) U voltage
Living electricity is 220V unit; Volt (V)
I current, unit: ampere (A)
COSφ power factor has no unit.
For purely resistive loads such as electric furnaces, electric water heaters, and other heating appliances; COSφ=1
The power calculation formula can be simplified as: P=U×I For electrical appliances with inductive loads such as fans and other motors, TVs, etc.; 1>COSφ>0 Motor electrical appliances are generally about 0.8. Current contains reactive components.
Household appliances generally do not have capacitive loads.
