"Home Circuit" Home Circuit and Safe Electricity PPT Courseware 3

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"Home Circuit" Home Circuit and Safe Electricity PPT Courseware 3

1. Understand household circuits

Household line → energy meter → main switch → fuse → electrical appliances, switches, sockets

Simplified circuit for home circuits

The function of a home circuit is to power various household appliances.

The switching on and off of various electrical appliances in a household circuit cannot affect other electrical appliances. Therefore, household appliances are connected to the circuit in parallel.

The functions of each component of the home circuit:

1. House entrance line

Connect to the outdoor power supply circuit, which is equivalent to the power supply of the household circuit.

2. Electric energy meter:

Responsible for recording the electricity consumed by each household in order to calculate how much electricity bills to pay.

There are ____ wires connected to the electric energy meter. How to connect them?

3. Knife switch:

(1) Function of knife switch

Makes and breaks electrical circuits to facilitate replacement of electrical appliances or repair of equipment.

(2) How should the knife switch be placed when installing?

4. Fuse:

In household circuits, excessive current may sometimes occur due to short circuit or excessive power, and it is necessary to install a fuse in the circuit to protect the circuit.

There is a fuse inside the fuse

a. Function of fuse:

When the current in the circuit is too large, the fuse will automatically blow.

b. Fuse material:

It is generally made of lead-antimony metal alloy with larger resistivity and lower melting point.

c. Fuse selection:

The current rating of the fuse is equal to or slightly greater than the normal operating current in the circuit.

2. Live line and neutral line

Generally, household circuits have two incoming wires, which are led from low-voltage transmission lines. One is called the live wire and the other is called the neutral wire. The live and neutral wires are the power source of the home circuit.

Neutral line------is connected to the earth, and there is no voltage between it and the earth.

The voltage between the live wire (also known as the phase wire) and the neutral wire or earth is 220 volts.

Ground wire------Some electrical appliances also need to add a wire connected to the earth called a ground wire to ensure the safe use of electrical appliances. (equivalent to the fire brigade of home circuits)

The wiring requirements are: "The live and neutral wires should be routed side by side. For vertical wiring, the fire is on the right, and for horizontal wiring, the fire is on the top. The hot wire is connected to the switch and then goes into the socket, and the neutral wire goes directly into the lamp holder."

communication, discussion

(1) Why should a high-value resistor be connected in series with the electric test pen?

Answer: Only when a high-value resistor is connected in series, the current passing through the human body will be very small, and the human body is safe.

(2) Why does the neon tube not light up when measuring the zero line with a test pen?

Answer: The voltage between the neutral line and the ground is 0V. At this time, no current is generated, which of course will not cause the neon tube to glow.

(3) When using a voltage test pen, why can’t you touch the metal body of the pen tip with your hand?

Answer: When you touch the metal body of the pen tip with your hand, there will be a voltage of 220V at both ends of the human body. The strong current generated at this time will flow through the human body, causing a safety accident.

(4) When a test pen is used to touch the live wire, the neon tube will glow. Is there any current flowing through the human body at this time?

switch:

The switch controls the light bulbs connected in series with it.

Connection notes:

1. The switch must be connected in series with the light bulb;

2. The switch must be connected to the live wire.

3. Incandescent light bulbs

1. Types of incandescent light bulbs

2. Principle of incandescent lamp

The filament of incandescent lamps is made of metallic tungsten. Tungsten has a very high melting point and can reach temperatures above 2000°C without melting. The tungsten filament in the bulb generates heat when energized, and the filament temperature reaches about 2000 degrees, reaching an incandescent state, so the filament emits bright light. People install the filament in a glass bulb and evacuate the bulb to avoid contact between the filament and the air and prevent oxidation of the filament. Generally, bulbs above 60W are filled with nitrogen, argon and other gases to hinder the sublimation of the filament at high temperatures.

Due to the relatively low luminous efficiency of incandescent bulbs, the country began to implement the "Incandescent Lamp Elimination Plan" on October 1, 2011. The plan is divided into five steps and will ban the sale of incandescent bulbs larger than 15W starting from October 1, 2016.

Class exercises

1. Correctly connect the lights and switches in the picture to the power cord.

2. In order to install a socket for studying at night, Mr. Mahu removed the chandelier switch at home and led out two wires, and then connected them to the socket. Please draw a schematic diagram of the circuit and explain what will happen if he does this.

3. How many errors are there in the wiring in Figure ①? Please point them out and explain them one by one.

There are three errors. The first mistake was that the knife switch was installed upside down. If you follow this installation method and open the switch blade, you will have to operate it with electricity when replacing the fuse. Moreover, the pulled blade may fall down to connect the circuit under the action of gravity, so it is very unsafe. The correct installation method should be with the static contacts at the top and the moving contacts at the bottom. The second mistake is to connect the socket in series to the live wire, which will affect the normal operation and safe use of electrical appliances. The third mistake was that the live and neutral wires of another socket were connected reversely.

4. As shown in the picture, the live and neutral wires are intact, but the light does not light up after S is closed. Use a test pen to test points a, b, c, d, e, and f in the picture. As a result, only point a can enable the test pen. If the neon tube emits light, the fault is ()

A. The wire between a and a is broken.

B. The wire between cd is broken

The wire between C and ef is broken

D. The filament of the light bulb is broken

Summary: Home Electrical Connections

1. The socket and electrical appliances are connected in parallel between the live wire and the neutral wire;

2. All electrical appliances are connected in parallel between the live wire and the neutral wire;

3. The electrical appliance and the switch that controls it are connected in series, and for safety reasons, when the live wire comes over, connect it to the switch first and then to the electrical appliance;

4. The sockets are divided into double holes and three holes, all of which are connected in parallel between the live wire and the neutral wire.

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For more information about the PPT courseware "Household Circuits, Home Circuits and Safe Use of Electricity", please click on the "Household Circuits ppt Home Circuits and Safe Use of Electricity ppt" tag.

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Update Time: 2024-11-23

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