Temporary electricity safety at the construction site 57 Q. How much do you know?


1. Under what circumstances should temporary power use be performed at the construction site?

A: The number of electrical equipment in the 5 and more than 5 or the total amount of equipment 50KW and 50KW or more. In addition, safety technology measures should be prepared.

2. What is the minimum safety distance between the outer edge of the construction project and the sideline of an overhead overhead line below 1KV?

Answer: 4 meters.

3. What is the “five prevention and one pass” that is required for the transformation and distribution room?

Answer: Five defenses: fire protection, waterproof, lightning protection, snow protection, and protection against small animals. One pass: keep it well ventilated.

4, the use of electrical equipment in accordance with the relevant safety regulations, the shell should have any protective measures?

Answer: Protective earth or zero.

5. How many times per minute should the patient be subjected to electrocardiographically induced cardiac arrest?

Answer: 60-80 times.

6. What three-level distribution box is used for temporary power use at the construction site?

A: The total distribution box, distribution box, switch box.

7. Why does the cover have to be covered when operating the knife opening and the magnetic switch?

Answer: To prevent electric arcing or fuse blowing and splashing in the event of a short circuit.

8. What warning signs must the electrician hang at the knife when the electrician is repairing?

Answer: "It is being repaired and it may not be closed."

9. What kind of protection system must be used in the power line directly connected to the ground at the neutral point of the construction site?

Answer: TN-S zero protection system.

10. What are the levels of safety voltage in China according to different environmental conditions?

Answer: 6,12,24,36,42 are safe voltage ratings.

11. How should the leakage protection of the distribution system of the construction site be equipped?

Answer: It should be set up in two levels and should have graded segmented leakage protection. A leakage protection is set in the switch box, rated leakage current is not more than 30mA, and customer-defined leakage action time should be less than 0.1s. Another level of leakage protection should be located in the main distribution box.

12. What material should be used to ground the grounding device?

Answer: The grounding body of the grounding device on the construction site should be made of round steel, steel pipe, angle steel, flat steel, etc. The rebar cannot be grounded.

13. What should be the signs of the distribution lines on the distribution panel (disc)?

Answer: Distribution lines on distribution boards (discs) should be numbered and marked for use.

14, what is the electric shock, what harm it to the human body?

A: Current flows through the human body into the ground or other conductors to form a conductive loop. This condition is called an electric shock. The human body is subject to a certain degree of injury when it is electrically shocked, and can be divided into electric shock and electric injury according to its form.

15. How does a common electric shock occur?

Answer: (1) The human body directly contacts the charged body.

(2) The human body is in contact with a malfunctioning electrical device.

(3) The distance from the charged body is too small.

(4) Step voltage electric shock.

16, what is a short circuit?

A: The two ends of the power supply are short-circuited directly, causing the current in the circuit to increase rapidly. This phenomenon is called a short circuit.

17. What is a circuit breaker?

A: The open circuit is a disconnection in the closed circuit, so that the current cannot be turned on.

18. What are the requirements for short-circuit protection?

Answer: Short-circuit protection should ensure that when a short-circuit occurs, or when a current close to the value of the short-circuit current appears, the power can be cut off reliably.

19. What are the requirements for overload protection?

Answer: Overload protection can guarantee the protection of the power supply when the load of the line or equipment exceeds the allowable range.

20. Grounding and zeroing can be divided into four ways according to their functions. Which four types should be mentioned?

Answer: (1) Working ground.

(2) Protective grounding.

(3) Protection zero.

(4) Repeatedly ground.

21, what is the neutral and neutral line?

Answer: (1) For a distribution transformer with a low voltage side star connection method, the common point of the three-phase coil is called the neutral point, and the wire from the neutral point is the neutral line.

(2) If the generator and transformer and the neutral point are grounded, then the neutral point at this time is called the zero point, and the neutral line is called the neutral line.

22, from the perspective of safety to understand why electrical equipment should be grounded?

A: From the security point of view:

(1) Eliminate leakage. If the electrical equipment of the electrical equipment has poor insulation properties, it will feel "hemp hands" when it is light and hurt people if it is heavy. If grounded, leakage current leaks from ground to earth, protecting personal safety.

(2) Avoid lightning strikes. The lightning arrester on electrical equipment is a device to prevent lightning strikes. It is necessary to bury the ground wire so as to lead the mine into the ground.

(3) Elimination of induction. Electrical equipment is electrostatically induced and if the chassis is grounded, induced charges can be safely introduced into the ground.

23, in the same distribution line does not allow part of the ground, the other part of the device zero, this sentence right?


24. In the power distribution system with protection and zero supply powered by the same transformer, can the protection zero and protection ground be used at the same time, and why?

Answer: (1) Cannot be mixed.

(2) If individual equipment has taken protective grounding measures and left the zero line network, the situation is quite serious. When a device with a protective earthing contact collides with a shell, the shell-to-ground voltage of the device and all other zero-connected devices also rises to 110 volts, so that all people who come in contact with the device and the zero-connected device are at risk of electric shock.

25. What are the basic requirements for the safety of electrical equipment in explosion-proof areas?

A: The basic principle of safety requirements for electrical equipment in explosion-proof places is the overall explosion protection. Integral explosion protection refers to the installation of the use of electrical power, communications, lighting, control equipment, instruments and meters, mobile electrical equipment (including power tools) and its transmission and distribution lines, etc., should be in accordance with the explosive hazard location Take appropriate measures to meet the requirements. If one of them does not meet the requirements of explosion hazardous locations, it cannot be said that the entire electrical explosion protection has been reached and there is a risk of explosion.

26. What are the two conditions for electrical fires and explosions?

Answer: (1) There are various flammable and explosive substances in the air of the place.

(2) Fire sources that cause fire and explosion in electrical installations.

27. What are the safety requirements for fire extinguishing of electrical equipment?

Answer: First of all, try to cut off the power and use appropriate fire extinguishers, such as carbon dioxide, difluoro chloromethane, dry powder and other fire extinguishers.

28. What safety measures should be taken to prevent fire and explosion accidents in electrical installations?

Answer: (1) According to the surrounding environment and the nature of production, choose the appropriate electrical device.

(2) The electrical device must not be overloaded.

(3) It is necessary to ensure the quality of the installation and maintenance of electrical devices so that they are in good condition.

(4) It is forbidden to store flammable and explosive materials in the vicinity of electrical devices and equipped with fire fighting equipment.

(5) Hot work must be handled for a hot work permit.

29. What are the basic requirements for lightning protection?

A: When directly struck by lightning, lightning currents can be rapidly introduced into the ground to ensure that lightning currents can be dispersed safely during discharge.

30. Why does a bad wire connector cause a fire?

Answer: The current flows through the wire connector and the device will generate heat. The amount of current generated is proportional to the size of the resistor. When the connector is not good, the contact resistance should be greatly increased. Therefore, the amount of heat is greatly increased, causing the insulating layer to burn out and cause a fire.

31. What is the safety distance between the project under construction and the nearby high-voltage lines?

A: The distance below 1KV is 4 meters; the distance between 1-10KV is 6 meters; the distance between 35-110KV is 8 meters; the distance between 154-220KV is 10 meters; and the distance between 350-500KV is 15 meters.

32. How are the distances and distances between the overhead lines of construction sites?

Answer: The span should not be greater than 35m; the distance between lines must not be less than 0.3m.

33. What are the regulations for the overhead section of the construction site?

Answer: The cross-sectional area of copper conductors is not less than 10 mm2, and the lead wire water is less than 16 mm2.

34. Why can't fuses be replaced with copper or iron wire?

Answer: Because the melting point of copper and iron wire is higher than the melting point of the fuse, when the current suddenly increases, it cannot be melted instantaneously, and the insurance effect of cutting off the current cannot be achieved, causing electrical equipment to catch fire due to short circuit or overload.

35. What are the safe voltage power supply ranges?

Answer: (1) When the outdoor lighting is less than 3m above the ground, and the interior lighting is less than 2.4m above the ground, 36V is used.

(2) The voltage of the power supply is not more than 36V.

(3) The power supply voltage for tunnels and civil defense projects should not exceed 36V.

(4) The supply voltage should not exceed 24V in wet and accessible live places.

(5) The lighting power supply voltage must not exceed 12V in a particularly humid place and in a metal container.

36, a complete set of lightning protection devices including what?

Answer: There are lightning rods, lightning protection nets, lightning protection strips, lightning receptors, deflectors, and grounding devices.

37. What should be the minimum horizontal distance between the edge of any part or hanging object of the crane and the overhead line below 10KV?

Answer: It must not be less than 2m.

38. Who should be responsible for guarding when erecting external electrical protection facilities?

A: There should be electrical engineering technicians or full-time security personnel responsible for monitoring.

39. What is TN-S zero protection system?

Answer: The neutral grounding system with a dedicated protection neutral line is called TN-S zero protection system, which is commonly called three-phase five-wire system.

40. What is the unified symbol for protecting the zero line?

Answer: Green/yellow bicolor lines.

41. What wires are prohibited from being used as load lines for electrical equipment?

Answer: Green/yellow bicolor lines.

42. What are the regulations for the installation height of the distribution box and the opening box?

Answer: The vertical distance between the bottom of the fixed box and the ground is 1.3-1.5. The vertical distance between the bottom of the moving box and the ground is 0.6-1.5 meters.

43. What are the regulations for the inlet and outlet of the conductor in the distribution box and the opening box?

Answer: The inlet and outlet openings should be located on the bottom surface of the box. It is forbidden to be installed on the top surface, side surface, rear surface or outside the box of the box.

44. What are the requirements for the installation height of lighting fixtures?

A: The indoor lighting fixtures should not be less than 2.4 meters away from the ground, and the outdoor lighting fixtures should not be less than 3 meters away.

45. How many lamps and outlets on the first single-phase circuit in the lighting system should not exceed?

Answer: 25.

46. Does the door of the power distribution room open inward or outward?

Answer: It should open outwards.

47. The leakage protection device used in hand-held power tools, what are the operating parameters?

Answer: The leakage protector with leakage current less than 15 mA and leakage action time less than 0.1 second should be used.

48. What are the rules for the protection of the zero line?

A: No openings or fuses must be installed on the protective zero line

49, protective grounding resistance, repeated grounding resistance, working grounding resistance, lightning protection grounding resistance What are the rules?

A: The working grounding resistance and the protective earthing resistance are no more than 4 ohms, and the repeated grounding resistance is no more than 10 ohms. The lightning protection and grounding resistance of the computer is no more than 30 ohms.

50. What is working ground?

Answer: The grounding of the neutral point on the low voltage side of the transformer is called the working ground.

51, what is protective grounding?

A: The protective earthing is to make a good electrical connection between the metal shell (or frame) and the grounding device that may not be charged when the electrical equipment is in normal operation and may show dangerous ground voltage.

52, what is the protection of zero?

A: The protection of the zero is to connect the metal shell or component of the equipment under normal circumstances to the direct connection with the system neutral wire.

53. What is repeated grounding?

Answer: In addition to the transformer neutral point grounded in the neutral point grounded power line, reconnecting to the ground at one or more locations on the zero line through the grounding device is called repeated grounding.

54. What is the distance between incandescent lamps, high-pressure mercury, combustibles and flammable structures?

Answer: 0.5 meters.

55. What are the main causes of electric shock?

Answer: (1) The use of defective electrical equipment, access to live, worn electrical wires, contact with ungrounded electrical equipment and bare wires, openings, insurance, etc.; (2) unprotected ground or ground wire quality; (3) ) Non-electrical workers perform electrical repairs; (4) Portable luminaries that do not use safe voltage according to regulations; (5) Lack of electrical hazard warning signs.

56. The fire at the construction site has occurred. Can it be extinguished with water and foam fire extinguisher?

Answer: No.

57. How should emergency aid be found when someone has an electric shock?

Answer: First, quickly connect the switch or use wood, wood and other non-conducting materials to separate the person who touched the electric shock from the contact electric parts; then lift it to a flat site for artificial first aid and report to the person in charge of the site.