Home circuit composition
Home circuit includes: entry line, power meter, main switch, fuse, light switch and socket.
(1) incoming line is a wire that causes indoors from the outdoors. There are two wires, one is a live wire (also known as phase wire ), and the other is a neutral wire. Under normal circumstances, there is a voltage of 220V between the live wire and the neutral wire. The neutral wire is usually grounded, and in this case there is also a voltage of 220V between the live wire and the ground wire.
(2) The power meter is used to measure the amount of electricity consumed by users, so it must be connected to the dry road. The rated voltage value and maximum current value are marked on the electricity meter. An energy meter marked "220V 5A" means that it is suitable for use in circuits with a total power of no more than 1100W.
(3) The main switch is used to control the on or off of the main circuit. Generally, the switch of the switch should be installed vertically, the clip holder (static contact) should be connected to the power cord, and the fuse should be installed below, and it should not be installed inverted. Some home circuits do not install master switches, but fuse boxes are installed there. The function is the same.
(4) fuse (also called fuse), is usually installed in a fuse box or in a fuse. The fuse is made of lead-antimony alloy , which has a relatively large resistivity and a low melting point. When the total current is too high, the fuse blows and automatically cuts off the circuit to prevent burning of electrical appliances and avoid fire. When the fuse is blown, the cause of the blow should be found first, and after troubleshooting, then replace the fuse with the appropriate specifications as required. Do not use ordinary copper wire or iron wire as fuses. Because the high melting points of copper and iron cannot play a role in the fuse, it may cause major accidents. You should not intentionally cause a short circuit to try whether the fuse will blow. This is absolutely not allowed.
(5) The protagonist of the home circuit is the light. Electric lights are a huge family. Including incandescent lamp , fluorescent lamp, high-pressure gas discharge lamp , etc. The light of the incandescent lamp is because the thin tungsten wire in the tunnel heats up after being powered on. The filament temperature is as high as about 2000 degrees Celsius, reaching the incandescent state, so the filament emits bright white light.
When installing the home circuit, each electrical appliance (including two holes and three hole socket ) is in parallel relationship, and a fuse (fuse box) must be installed on the live line. Connect the neutral wire on the left and the live wire on the right. When connecting an incandescent light, the switch must be connected to the live wire, and the live wire must be connected to the tin point on the screw head, and the neutral wire must be connected to the spiral sleeve.
(6) switch: It can control the on and off of each branch. The switch should be connected in series with the controlled electrical appliance and must be connected to the live wire.
(7) Socket: There are two-hole sockets and three-hole sockets for plugging into TVs, washing machines, electric fans and refrigerators. The socket must be connected in parallel with the lamp holder. The socket has three holes, its two holes are connected to the live wire and the neutral wire respectively, and the other hole is connected to the earth.
Only those electrical appliances with metal shells (or electrical appliances that are prone to moisture) will use a triple-pin plug. In the three-hole socket, except for the two holes connected to the live wire and the neutral wire, the other hole is connected to the ground, that is, the three-pin plug on the household appliance, and the two-pin plug connected to the electrical parts (such as motor in the refrigerator and washing machine). The other pin corresponding to the grounding jack is connected to the housing of the household appliance. In this way, plug the three-pin plug into the three-hole socket, and while connecting the electrical part into the circuit, it also connects the shell to the ground. Why do this? The metal shell of household appliances was originally insulated from live wires and was not charged, so there was no danger of human contact with the shell. However, if the internal live wire insulation skin is damaged or loses its insulation performance, causing the live wire to be connected to the shell, and the shell is charged, and the human body contacts the shell equals contacting the live wire, a melting accident will occur.If the shell is grounded with wires, even if the shell is charged, it will flow away from the grounding wire and the human body will contact the shell without any danger.
(8) test pen
test pen is used to distinguish between live wire and neutral wire: use your hand to contact the metal body of the pen tail, the tip of the pen contacts the wire (or the conductor connected to the wire). If the neon tube emits light, it means that it is contacting the live wire: if the neon tube does not emit light, it means that it is contacting the neutral wire. It should be noted that when using an electric pen, the hand must contact the metal body of the pen tail. If the hand does not contact the metal body of the pen tail, even if the tip of the pen touches the live wire, the neon tube will not shine, and the electric pen will lose its function. Only when a human hand touches the metal body at the end of the pen, will the current flow through the neon tube and enter the earth through the human body. Only then will the neon tube shine. Why don’t people get electrocuted at this time? Because there is a resistor with a large resistance value in the electric pen, which is more than one megohm. When using a test pen to contact the neutral and ground wires, since there is no voltage between the neutral and ground wires , of course, no current flows through the neon tube, so the neon tube does not emit light. When using an electric pen, human hands must not touch the metal body of the pen tip, as a large current will flow through the human body and cause an electric shock accident.
The reason for excessive current in the home circuit
(1) Short circuit occurs: a short circuit means that the current directly connects the neutral and live wires without passing through the electrical appliances. This is equivalent to a wire with very small resistance connected in parallel with other electrical appliances. According to the law of resistance in the parallel circuit, the total resistance in the circuit is smaller. According to Ohm's law , it can be calculated that the current in the dry circuit can reach several hundred amperes at this time, causing the fuse to blow instantly.
(2) The total power of the appliance is too large. When there are too many electrical appliances connected to the circuit, according to the formula P=UI, there is
I=P/U, and
Voltage between live wire and neutral wire
U=220V is certain, so the larger the total power P, the greater the current I in the trunk circuit, and when the current I reaches a certain level, the fuse can be blown.
safe electricity use Common sense
(1) The magnitude of the current through the human body is determined by the applied voltage and the resistance of the human body;
(2)Safe voltage: Only voltages not higher than 36 volts are safe;
(3) The voltage of the home circuit is 220 volts, and the voltage of the power circuit is 380 volts.
(4) Electric shock accident is caused by excessive current passing through the human body. The greater the current passing through the human body, the longer the power is, and the more dangerous it is.
(5) Electric shock accidents in home circuits are caused by the direct or indirect connection of the human body with the live wire.
Two forms of low voltage electric shock:
Single-line electric shock: When a person standing on the ground touches the live line, the current enters the human body from the live line to the ground, and forms a loop through the ground line, causing an electric shock accident.
Double-wire electric shock: If a person standing on an insulator touches two wires at the same time, the current will enter the human body from the live wire to another wire (neutral wire) and form a circuit, causing an electric shock accident.
So, for safe use of electricity, never contact live wires without insulation and conductors connected to live wires.
So what should we be particularly wary of when using electricity in daily life? That is, you must be particularly alert to the insulated objects that are originally insulated to conduct electricity, but objects that are originally not supposed to be charged are charged.
For example: ① Pay attention to prevent damage to the insulation part. ② Keep the insulating part dry, do not use wet hand to turn the switch, and do not dry clothes on the wire. ③ If someone is electrocuted, they must first cut off the power supply, or use a dry wooden stick and other insulator to clear the wires. ④When erecting a TV antenna, be careful not to touch the wires. If the electrical appliance has a metal shell, it must be grounded. Therefore, the principle of electricity consumption for low-voltage charged bodies is to not contact the low-voltage charged bodies.
(6) Two forms of high voltage electric shock
Have students seen this logo? This is a sign of high pressure danger.
High voltage arc electric shock: When the human body is close to the high voltage charged body and reaches a certain distance, discharge will occur between the high voltage charged body and the human body. At this time, an electric current passes through the human body, causing high-voltage arc electric shock.
step voltage electric shock : The high-voltage transmission line falls on the ground, and there is voltage at various points on the ground at different distances from the wire's broken head. When a person approaches the broken head, the two feet are located at different positions far and near the broken head, so there is a voltage (step voltage) between the two feet. At this time, the current passes through the human body, causing electric shock to the step voltage.
So, for safe use of electricity, do not get close to high-voltage charged bodies.
First aid for electric shock:
First, you cannot directly pull the person who is electrocuted, otherwise the person who goes to rescue will also be electrocuted. The power should be cut off quickly, or the wire should be lifted open with a dry wooden stick, etc., so that the person who was electrocuted should be removed from the power supply quickly. When a fire occurs, you must first cut off the power supply and never splash water on the fire with electricity.
