1. Why must lighting switches be connected to the live wire?
If a lighting switch is installed on the neutral wire, although the light will not turn on when the switch is off, the live wire of the lamp holder remains connected. People will mistakenly believe that the power is off because the light is off. In reality, the voltage to ground at various points on the lamp is still a dangerous 220 volts. If people touch these actually live parts when the light is off, it will cause an electric shock. Therefore, all lighting switches or switches for single-phase small-capacity electrical equipment must be connected in series with the live wire to ensure safety.
2. How should a single-phase three-hole socket be installed correctly? Why?
Generally, single-phase electrical equipment, especially portable equipment, should use a three-prong plug and a matching three-hole socket. Three-hole sockets have a dedicated protective grounding (neutral) socket. When using grounding protection, some people often simply connect this socket's terminal to the neutral wire inside the socket, which is extremely dangerous. If the neutral wire is disconnected, or if the live (phase) and neutral wires are reversed, the metal parts of the socket, such as the casing, will carry the same voltage as the power supply, leading to electric shock.
Therefore, when wiring, the dedicated grounding socket should be connected to a dedicated protective grounding wire. When using neutral grounding protection, the neutral wire should be drawn from the power supply end and should not be used from the neutral wire of the nearby socket.
3. Why is it strictly forbidden to bury plastic-insulated wires directly in the wall?
(1) After long-term use, plastic insulated wires will age and crack, greatly reducing the insulation level. When the line is overloaded or short-circuited for a short time, the insulation will be damaged more easily.
(2) Once the wall gets damp, it will cause a large-scale electrical leakage, endangering personal safety.
(3) Directly burying plastic insulated wires is not conducive to line inspection and maintenance.
4. Why use a residual current device (RCD)?
A residual current device (RCD), also known as a residual current circuit breaker, is a new type of electrical safety device. Its main uses are:
(1) Prevent electric shock accidents caused by leakage of electrical equipment and electrical lines.
(2) Prevent single-phase electric shock accidents during the use of electricity.
(3) Promptly disconnect single-phase grounding faults in electrical equipment to prevent electrical fire accidents caused by leakage.
(4) With the improvement of people's living standards and the continuous increase of household appliances, electric shock and fire accidents caused by defects in electrical equipment, improper use and inadequate safety technology measures during the use of electricity have caused unnecessary losses to people's lives and property. The emergence of leakage current protection devices provides a reliable and effective technical means to prevent the occurrence of various accidents, cut off the power supply in time, and protect equipment and personal safety.
5. What are the main causes of electric shock accidents?
Statistical data shows that the main causes of electric shock accidents are as follows:
(1) Lacking electrical safety knowledge, flying kites near high-voltage lines, climbing high-voltage poles to steal bird nests; using hands to pick up live wires after a low-voltage overhead line breaks without disconnecting the power; touching live parts while connecting wires at night; touching damaged plastic-covered knife switches.
(2) Violating operating procedures by connecting live lines or electrical equipment without taking necessary safety measures; touching damaged equipment or wires; accidentally climbing onto live equipment; connecting live lighting fixtures; repairing live power tools; moving live electrical equipment; turning on light bulbs with wet hands, etc.
(3) The equipment is unqualified, the safety distance is insufficient; the grounding resistance of the two-wire-one-ground system is too large; the grounding wire is unqualified or the grounding wire is broken; the insulation is damaged and the wire is exposed, etc.
(4) Equipment is in disrepair, the line is broken or the pole is blown down by strong wind and not repaired in time; the bakelite of the knife switch is damaged and not replaced in time; the motor wire is broken, causing the casing to be electrified for a long time; the porcelain insulator is damaged, causing the phase wire and the pull wire to be short-circuited, and the equipment casing is electrified.
(5) Other accidental causes, such as touching a live wire that has fallen to the ground while walking at night.
6. What first aid measures should be taken in the event of electric shock?
In the event of an electric shock, while ensuring the safety of the rescuer, it is essential to first try to quickly disconnect the victim from the power source before proceeding with the following emergency repairs.
(1) Loosen the tight clothing that is obstructing the breathing of the person who has been electrocuted.
(2) Check the mouth of the person who has been electrocuted, clean the mucus in the mouth, and remove dentures if present.
(3) Immediately begin on-site rescue. If breathing stops, use mouth-to-mouth resuscitation. If the heart stops beating or is beating irregularly, perform chest compressions. Never interrupt the rescue without a valid reason.
If there is a second person present at the scene besides the rescuer, the following should also be done immediately:
(1) Provide first aid tools and equipment.
(2) Persuade any unauthorized personnel at the scene to leave.
(3) Ensure adequate lighting and air circulation at the site.
(4) Report to the leader and ask the doctor to come and save the patient.
Experimental studies and statistics show that if rescue efforts begin one minute after an electric shock, 90% of victims can be saved; if rescue efforts begin six minutes after an electric shock, the chance of survival is only 10%; and if rescue efforts begin 12 minutes after an electric shock, the chance of survival is extremely small. Therefore, when someone is found to have been electrocuted, every second counts, and all possible methods should be used.
7. What measures can be taken to ensure safe electricity use in the home?
With the widespread use of household appliances, it is crucial to master the knowledge of safe electricity use and ensure electrical safety.
(1) Do not buy counterfeit or substandard household products that are not made by the manufacturer.
(2) Household appliances should have complete and reliable power cord plugs. Household appliances with metal casings should be grounded.
(3) Switches and fuses must not be installed on the ground wire or the neutral wire. It is forbidden to connect the ground wire to the water or gas pipeline.
(4) Do not touch live equipment with wet hands, and do not wipe live equipment with a wet cloth.
(5) Do not illegally connect or extend electrical wires, and do not move electrical equipment at will.
(6) When inspecting and repairing household appliances, the power must be disconnected first.
(7) When the power cord of a household appliance is damaged, it should be replaced immediately or wrapped with insulating cloth.
(8) When a fire occurs in a household appliance or electrical wire, the power supply should be disconnected before extinguishing the fire.
8. How to prevent household appliances from burning out?
The rated voltage of commonly used household appliances is 220 volts, and the normal supply voltage is around 220 volts. When the power supply line experiences a sudden voltage spike due to natural disasters such as lightning strikes, unbalanced three-phase loads, a broken neutral wire due to aging or improper wiring, or a rise in phase voltage caused by human error, the increased current can lead to overheating and damage to household appliances. To prevent damage to household appliances, the following measures should be taken: First, disconnect the power supply when electrical equipment is not in use; second, upgrade old and dilapidated service lines; and third, install residual current circuit breakers (RCCBs) with overvoltage protection.
9. How should fuses be selected for residential use?
For residential use, fuses should be selected according to the electricity capacity. For example, when using a 5-amp meter, the fuse should be greater than 6 amps but less than 10 amps; when using a 10-amp meter, the fuse should be greater than 12 amps but less than 20 amps. In other words, the selected fuse should be 1.2 to 2 times the meter's capacity. Only one fuse that meets the specifications should be selected; multiple small-capacity fuses should not be used together, and copper wire should never be used as a substitute for a fuse.
10. What are the basic requirements for residual current devices (RCDs)?
Technically, the following requirements should be met:
(1) The sensitivity of the electric shock protection should be correct and reasonable. Generally, the starting current should be in the range of 15~30 mA.
(2) The operating time of electric shock protection should generally not exceed 0.1 seconds.
(3) The protector should be equipped with necessary monitoring equipment to prevent it from losing its protective function when the operating state changes. For example, for voltage-type electric shock protectors, a device for grounding the neutral wire should be installed.
