Current situation and solutions of temporary power

Current situation and solutions of temporary power use on the construction site

the safety of temporary power use on the construction site is the basis for ensuring the normal construction of construction projects, and it is a guarantee work that must be done well before and during the construction of construction projects. Temporary electricity use is a project prone to casualties at the construction site, and electric shock is one of the five major injuries in the construction field

in order to regulate the temporary use of electricity on the construction site and prevent the occurrence of electric shock casualties, the Ministry of construction has prepared the technical code for safety of temporary use of electricity on the construction site (JGJ), which has been implemented for many years, and the electric shock casualties on the construction site have been greatly reduced. According to the problems existing in the implementation, it was later revised, numbered JGJ, and implemented from July 1st, 2005. In the newly revised technical code for safety of temporary electricity on construction site (hereinafter referred to as the code), 25 mandatory standard provisions have been added, requiring all construction units to do so. Among them, the 220/380v three-phase four wire low-voltage power system with direct grounding of the neutral point of the power supply dedicated to the temporary power engineering at the construction site must meet the following requirements: ① three-level distribution system is adopted; ② TN-S neutral protection system is adopted; ③ Adopt secondary leakage protection system. In addition, it also puts forward clear requirements for the preparation of temporary power use organization design. That is, when designing and changing the temporary electricity organization, the procedures of "preparation, review and approval" must be performed. The preparation shall be organized by the electrical engineering technicians and implemented after being reviewed by the relevant departments and approved by the technical director of the enterprise with legal personality. In addition, the specification also puts forward corresponding mandatory standard provisions for the protection of external power lines and electrical equipment, grounding and grounding resistance, lightning protection, power supply of distribution rooms and equipment, distribution lines, distribution boxes and switch boxes, electric construction machinery and hand-held electric tools, lighting and other items. I won't repeat it here

the newly revised code has been implemented for more than two years. From the supervision and inspection of various construction sites, there are many problems, and the temporary power consumption of a small number of construction sites is far from the requirements of the code. It is mainly manifested in:

1. The preparation of temporary power use organization design is not standardized or not prepared

(1) the temporary power use organization design of some construction sites is not organized and prepared by professional electrical engineering technicians, but by constructors, safety officers or electricians, which can not be used to guide site construction at all. Some only write out the plan or the preparation, review and approval do not conform to the procedures

(2) the compilation content is simple and not targeted. The Code stipulates that the temporary power utilization organization design should include 8 items, but some only have 2-3 items; Some calculate the power consumption directly without counting the number of mechanical equipment, and the calculation results are groundless; Some do not have overhead lines and external power protection, but copy the regulations in the specifications; JGJ is still used in some temporary electricity organization designs

2. Incomplete safety technical files

there is no acceptance form after the completion of temporary power construction; There is no checklist during operation; The electrician did not install it, which made tepex the preferred material for mass production, inspection, maintenance and demolition work records; There is no record sheet for measuring grounding resistance, insulation resistance and leakage action parameters of leakage protector

3. The protection of external power lines and electrical equipment is not in place

the distance between the external power lines and transformers on some construction sites and the scaffolding outside the building is less than the specification, and some are even within the radius of the tower operation, but there are no protective measures or the protective height is not enough, so there are not only major hidden dangers of accidents, but also electric shock accidents

4. Grounding and lightning protection are not standardized

the specification strictly stipulates that "the purpose of not using the experimental machine is" this article can help us get some equipment to do protective neutral connection and other equipment to do protective grounding ", but a few construction sites still do this, or the number of repeated grounding groups cannot meet the requirements. The specification stipulates that the protective zero line in TN system must be repeatedly grounded at the distribution room or general distribution box, and also at the middle and end of the distribution system, that is to say, there must be no less than three groups of repeated grounding at the construction site. However, during the inspection, it was found that a small number of construction sites (especially joint venture teams) only made a group of repeated grounding at the main distribution box, and some construction sites made repeated grounding bodies at the switch box, not angle steel, steel pipe or smooth round steel, but deformed steel

5. The distribution room

specification stipulates that the distribution room is close to the power supply and should be located in a place with less dust, less moisture, less vibration, no corrosive media, no inflammables and explosives and smooth roads. During the supervision and inspection, it was found that some distribution boxes and general distribution boxes were not set high enough, which was easy to water, there was no safety fence around, and there was no normal lighting and accident lighting in the room

6. The specification for distribution lines stipulates that there are two setting methods: overhead lines and buried lines. For buried lines, the buried depth should not be less than 0.7m, and fine sand not less than 50mm thick should be evenly laid on the upper, lower, left and right sides of the cable, and then covered with hard protective layers such as bricks or concrete slabs. However, most of the construction sites cannot do this, most of them are placed on the ground, and some of them are buried underground, but the depth is very shallow, forming a section of exposed and a section of concealed, and there is no protection when crossing the road. It is easy to damage the cable sheath when the car is rolled and stepped on. It is stipulated in the provisions of the mandatory standard that "five core cables must contain light blue and green/yellow insulated core wires. Light blue core wires must be used as n wires; green/yellow core wires must be used as PE wires, and mixing is strictly prohibited". Some construction sites may use the green/yellow core wire as n wire, which seriously violates the provisions of the specification. There are also unsafe factors everywhere, such as the wires and cables at some construction sites are pulled and connected disorderly, or wrapped on steel pipes, or pressed under steel bars, which are not wrapped tightly. Fancy wires and colloidal wires are used on site, and the cables used for tower cranes are not fixed with porcelain bottles

7. Distribution box and switch box

the specification stipulates the material, specification, size, purpose, installation position and height of the main distribution box, distribution box and switch box used in the construction site, and also stipulates the types of electrical settings in various electrical boxes. However, from the supervision and inspection of the construction site, it is far from the requirements of the code. For example, some general distribution boxes, distribution boxes and switch boxes are transported from the last construction site, which are very dilapidated; Some are processed and made by the project department, which is extremely non-standard; Some are bought from the market, which are neither products recorded in the safety supervision department, nor have they reached 3C certification. In addition, the height of switch boxes installed on many construction sites with clean and kerosene soaked cotton yarn and the distance from electrical equipment cannot meet the specifications. Most mobile machines such as cutting, vibrating rods and hand-held electric tools are not equipped with mobile switch boxes. The installation position of some switch boxes is unfavorable, and the operation is excluded from the following three aspects. There are also many places where reinforcement processing products, square timber, formwork, steel pipes and other items are piled around the distribution box and switch box, which violates the regulations that "there should be enough space and channels for two people to work at the same time around the distribution box and switch box, and no items that hinder operation and maintenance should be piled,..."

the electrical setting in the electrical box violates the regulations, such as the disconnector installed in the distribution box does not have a visible breaking point. Some of the switch boxes are equipped with several plugs; Most of them are equipped with handle switches (such switches shall not be used on the construction site); Some are only installed with leakage protectors, which can not meet the requirements of "one machine, one switch, one box and one leakage"; The sequence of leakage protector and disconnector in some switch boxes is reversed; There are also very few construction sites that still use wooden switch boxes and surface mounted disconnectors, or use reverse switches instead of disconnectors, etc

8. The specification for electric construction machinery and hand-held electric tools stipulates that "the metal shells of motors, high-voltage devices, electrical appliances, lighting appliances and hand-held electric tools must be connected to neutral for protection." In our daily supervision and inspection, we found that most construction sites failed to do so, including various types of reinforcement processing machinery, woodworking saws, cutting machines, etc. In addition, dysprosium lamps and iodine tungsten lamps used on site have been using two core cables, so it is impossible to connect the shell protection to zero. At present, when installing formwork at many construction sites, in addition to using woodworking saws on the site, most of them still use hand-held cutting machines on the operation surface, without setting switch boxes, and only connect with sockets