"Safe Use of Electricity" Inseparable Electricity PPT Courseware 3

"Safe Use of Electricity" Inseparable Electricity PPT Courseware 3

1. The harm of electric current to human body

There are three types of harm caused by electric current to the human body: electric shock, electric injury and electromagnetic field injury.

1. Electric shock refers to the passage of electric current through the human body, destroying the normal functions of the human heart, lungs and nervous system.

2. Electrical injury refers to the harm caused to the human body by the thermal, chemical and mechanical effects of electric current; it mainly refers to arc burns, burns caused by splashing of molten metal, etc.

Physiological damage from electromagnetic fields means that under the action of high-frequency magnetic fields, people will experience neurological symptoms such as dizziness, fatigue, memory loss, insomnia, and dreaminess.

3. Damage caused by electric current to human body

Factors affecting the degree of injury: current size, action time, current path, current type and frequency, voltage, human body resistance, the constitution and health of the person who received the electric shock, and surrounding environmental conditions. The relationship between the degree of damage and the size of the current:

1) Perceived current - the minimum current that causes human sensation. Male 1.1mA/Female 0.7mA

2) Get rid of current - the maximum current that can independently get rid of the power supply after an electric shock. Male 16mA/Female 10mA

3) Fatal current - a current that can endanger life in a relatively short period of time. (ventricular fibrillation current) (50mA)

2. The harm of electric current to human body

It is generally believed that the danger of electric current passing through the heart, lungs and central nervous system of the human body is relatively high, especially when the electric current passes through the heart, the risk is greatest. So the current path from hands to feet is the most dangerous.

People who get electric shock can also easily fall due to violent spasms, causing electric current to pass through the body and causing secondary accidents such as falls and falls.

3. Technical measures to prevent electric shock

Insulation, screening and spacing are the most common safety measures

1. Insulation

It prevents the human body from touching the insulator and seals the live body. Porcelain, glass, mica, rubber, wood, bakelite, plastic, cloth, paper and mineral oil are all commonly used insulating materials.

It should be noted that many insulating materials will lose their insulation properties when exposed to moisture or will be damaged and lose their insulation properties under the action of strong electric fields.

2. Screen protection

That is, barriers, passports, protective cover box gates, etc. are used to isolate live objects from the outside world.

Generally, the movable part of an electrical switch cannot be insulated, but needs to be screened. High-voltage equipment, regardless of whether it is insulated or not, should be screened.

3. Spacing

Just ensure the necessary safety distance. In addition to preventing contact with or excessive proximity to live objects, the spacing can also play a role in preventing fires, preventing line mixing, and facilitating operation. In low-voltage work, the minimum inspection distance should not be less than 0.1 meters.

Ground and zero

ground

Refers to the direct connection with the earth. A certain point of an electrical device or a live part of an electrical line is connected to the earth. An artificial connection between a certain point of a non-live part of an electrical device or other device and the earth when it is normal is called grounding.

Protective grounding

Protective grounding - Protective grounding is a good electrical connection between the metal casing (or frame) and the grounding device where the electrical equipment is not energized during normal operation but may present dangerous ground voltages in the event of a fault.

Protective grounding measures should be taken for metal parts that may exhibit dangerous voltages due to insulation damage or other reasons. Metal shells of motors, transformers, switchgear, lighting fixtures and other electrical equipment should be grounded. In general low-voltage systems, the protective ground resistance value should be less than 4 ohms.

Applicable places for protective grounding: It is suitable for ungrounded or high-impedance grounded distribution networks of different types and voltage levels to form IT systems. In addition, in a three-phase four-wire distribution network with a rated voltage of 0.23/0.4kV and a low-voltage neutral point directly grounded, if a leakage protection device is installed, protective grounding measures can also be used to form a TN system

Install leakage protection device

In order to ensure the safety of people and equipment in the event of a fault, leakage current action protectors should be installed as much as possible. It can convert and obtain abnormal signals through the detection mechanism of the protection device when the equipment and circuits leak electricity, convert and transmit them through the intermediate mechanism, and then prompt the actuator to act and automatically cut off the power supply to play a protective role.

Use safe voltage

This is a safety measure used on small electrical equipment or small capacity electrical lines. According to Ohm's law, the greater the voltage, the greater the current. Therefore, the voltage that may be applied to the human body can be limited to a certain range, so that under this voltage, the current passing through the human body does not exceed the allowable range. This voltage is called a safety voltage. The effective power frequency value of the safe voltage does not exceed 50 volts, and the DC value does not exceed 120 volts. Our country stipulates that the power frequency effective value levels are 42 volts, 36 volts, 24 volts, 12 volts and 6 volts.

Precautions

1. Do not tamper with or repair the electrical equipment in the workshop without permission.

2. Distribution boxes, distribution boards, blade switches, push button openings, sockets, plugs and wires that are frequently contacted and used must be kept intact and must not be damaged or have live parts exposed.

3. Do not use copper wires instead of fuses, and keep the covers of knife switches, magnetic switches, etc. intact to prevent arcing or splashing when the fuse blows and hurts people during a short circuit.

4. Always check the protective grounding and zero connection devices of electrical equipment to ensure that the connections are firm.

5. When moving electric fans, lights, welders and other electrical equipment, the power supply must be cut off first and the wires must be protected to avoid wear or breakage.

7. Principles of first aid for electric shock

(1) Principles for rescuing victims of electric shock on site

The principles of on-site first aid for electric shock can be summarized in eight words: quickly, on the spot, accurately, and persistently.

(1) Quickly. All other conditions being equal, the longer the electric shock lasts, the greater the possibility of ventricular fibrillation and even death.

(2) In situ. The person performing the rescue must carry out gun rescue on the spot near the scene. Never send the person to the power supply department or hospital for rescue over a long distance, so as not to delay the best and precious rescue time.

(3)Accurate. The rescuer's artificial respiration must be in position accurately and in a standardized manner.

(4) Persistence. As long as there is one percent hope, we must make one hundred percent effort to rescue.

(2) Disconnect from the power supply:

1. Methods to quickly remove electric shock victims from the power supply

There are generally two methods to remove an electric shock victim from the power supply: one is to immediately disconnect the power supply of the conductor or equipment touched by the electric shock victim; the other is to try to remove the electric shock victim from the live parts.

1) If the power switch or plug is near the location of electric shock, pull the switch or pull out the plug immediately.

2) If the location of the electric shock is far away from the power switch, you can use tools such as electrician's pliers with insulated handles or an ax with dry wooden handles to cut off the wires.

3) If the conductor falls on the person who gets an electric shock or the body of the person who gets an electric shock presses the conductor, use dry clothes, gloves, ropes, wooden boards and other insulating materials as tools to pull away the person who gets the electric shock or remove the conductor.

4) If the clothes of the person who received an electric shock are dry and not tightly wrapped around his body, he can pull the back of his clothes to drag him away from the live part; at this time, the rescuer shall not cover the person who received an electric shock with his clothes, and shall not directly pull the person who received an electric shock. The patient's feet and body as well as contact with surrounding metal objects.

5) If the rescuer has a well-insulated tool in his hand, he can also pull the electrocuted person's feet away from the live part.

6) If the person who gets an electric shock is lying on the ground, insulating objects such as wooden boards can be inserted under the person to block the current.

Summary: pull, cut, pick, pull, pad, throw.

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