Household distribution box is also called strong current box, which is generally composed of box, leakage switchgear and metering equipment.
The household distribution box belongs to the end protection device of household electricity. Its function is to cut off and connect the power supply and effectively control each line. The incoming end of the distribution box is connected to the outgoing side of the watt hour meter, and the outgoing end is connected to the home appliances, which is the last guarantee for the safety of household electricity.
1、 Box
1. At present, the distribution boxes on the market mainly include metal shell and plastic shell. The installation methods include concealed installation and open installation. The box needs to be intact according to the actual needs of the family.
2. Zero line bar and ground line bar (grounding protection) shall be set at the wiring confluence in the box of the household distribution box to ensure that the whole and accessories are in good condition. It is recommended to test the insulation of the box with an electric pen, and a transparent window for inspection shall be set on the door panel of the distribution box.
3. Before selecting the box size, first determine the number of leakage switches / air switches, and select the appropriate box size according to the number and size of accessories. It is recommended to consult professionals for reference.
2、 About ground wire
The function of the ground wire is to introduce the charged current of the electrical shell into the earth. Electric leakage will lead to the electrification of the electrical shell. When the human body contacts the charged metal shell, the resistance of the human body is greater than the resistance of the ground wire to the current. At this time, the current will be introduced into the earth along the ground wire, so as to ensure human safety. The ground wire shall be separately connected to the ground wire row, which can reduce the risk of human contact with the charged metal shell. If all the ground wires are screwed together and connected to the ground wire row, the ground wire has only one connection point on the ground wire row, and the problem of this connection point will lead to the loss of protection of all the ground wires in the room.
3、 About zero line
The zero line, also known as the neutral line, is led out from the neutral point on the secondary side of the transformer and forms a loop together with the phase line to supply power to the electrical equipment. Under normal circumstances, the zero line is repeatedly grounded with the ground wire at the neutral point on the secondary side of the transformer to play the role of double protection.
4、 Total open
The national standard installation and operation of leakage protector stipulates:
Electrical equipment powered by single-phase 220V power supply can be equipped with two-level two-wire or single pole two-wire leakage protector.
1. Single pole / single P two-wire leakage protector only has live wire protection, that is, the single pole protection in the above figure. In case of fault, the live wire will be cut off. At this time, the zero wire is still normal. The zero wire must be connected to the terminal marked n, and wrong connection is not allowed. (wiring: two wires in and two wires out)
2. The two-level / double P two-wire leakage protector has both live line and zero line protection, which is the bipolar protection in the figure above. In case of fault, the live line and zero line are cut off together. (wiring: two wires in and two wires out)
In home decoration, it is recommended to use double pole / double P main switch for the selection of main switch. The main switch of household distribution box generally selects two pole / 2p, 40A and 63A miniature circuit breakers, with or without leakage protection.
To determine the size of the total opening, the following three factors shall be considered:
Factor 1: current parameters of electricity meter.
For example, 5 (20) a, 10 (40) a, 15 (60) a, etc. will be marked on the meter. The number in brackets represents the maximum current that the meter can withstand, and the main switch in the house can only be less than or equal to this number.
Factor 2. Long term safe carrying capacity of incoming bus.
At present, houses and shops generally use single-phase electricity, and three wires are laid through pipes (buried in the wall) to the home. The long-term safe current carrying capacity of incoming wires should be considered.
Factor 3: indoor socket load.
If the load of the main switch is less than the indoor power load, the main switch will trip.
5、 Leakage protector
Leakage protector, also known as leakage switch, is used to prevent personal electric shock and electrical fire in case of short circuit to ground due to circuit / electrical damage. It is generally installed on the socket circuit of each household distribution box and the power incoming line of the general distribution box of the whole building.
1. When the phase line of the protected line is connected to the earth directly or through an unexpected load, an approximate sinusoidal waveform is generated, and its effective value is the slowly changing residual current. When the current is greater than a certain value, the protector cuts off the line to play a protective role.
2. In home decoration, leakage protectors are often used in circuits easily accessible to human body, such as ordinary sockets of distribution box, kitchen sockets, toilet sockets and so on.
3. 16a and 20A leakage protection switches are generally selected for socket circuit. However, the kitchen and toilet generally need about 25A leakage protection switch; 10A and 16A miniature circuit breakers are generally selected for lighting circuit; 1.0-1.5p air conditioning circuit generally selects 16a-25a miniature circuit breaker; The 3-5p cabinet machine needs 25a-32a, and the central air conditioner of about 10p needs about 2p40a.
Setting leakage protector in low-voltage distribution system is not only one of the effective measures to prevent personal electric shock accidents, but also a technical measure to prevent electrical fire and electrical equipment damage accidents caused by leakage, but prevention should still be given priority in operation.
6、 Air switch
1. Air switches are also called air circuit breakers. The principle of the air switch is to use air as the insulating medium to turn on the current in the circuit, so as to generate heat for the components, promote the bimetallic sheet inside to bend upward after receiving heat, push the lever, open the locked latch and cut off the power supply, so that the air switch will trip automatically, so as to achieve the function of protecting the current. (generally, automatic tripping is caused by overload or short circuit of the circuit)
2. The air switch is generally used to prevent the circuit from carrying too much load for a long time. In order to prevent human electric shock, it only plays the role of fuse; The leakage protector is to prevent electric shock and leakage of human body, and will not play a great role in the overload of circuit. Because of their different working principles, the safety protection is also different, so they can not be blindly mixed.
3. In terms of tripping, the air switch passes through the live line and zero line. If the current between the two lines is too large, it will cause tripping. The leakage protector is only because of the live wire. When the human body contacts the live wire, it will form a loop with the ground, so that the device inside will automatically feel and achieve the purpose of tripping.
4. In home decoration, air switches are generally used on circuits that are not easily accessible to the human body, such as lighting, air conditioning hanging up, etc.
Note: household distribution box is mainly composed of distribution box box (including zero line row and ground line row), general switch (bipolar), leakage protector and air switch.
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