Temporary power system in construction site

Study on Code for Temporary Electricity Consumption in Building Construction

1, ① three-level distribution system;

② TN-S neutral point protection system is adopted;

③ Adopt secondary leakage protection system.

2. Three-level power distribution: it is equipped with three standard electrical boxes: general distribution box, sub-distribution box and switch box.

3, switch box should be consistent with one machine, a box, a brake, a leak.

4, all kinds of electrical appliances in the three types of electrical boxes should be qualified products; 5. Two-level protection: leakage protectors with capacity requirements and qualified quality shall be selected in the main distribution box and switch box. This is not only conducive to the maintenance of on-site electrical system, but also can fully ensure the construction safety, and it is also the embodiment of on-site standardized management and civilized construction. Therefore, it is very important to set up "three-level distribution and two-level protection" reasonably.

The temporary electricity consumption of some construction sites is far from meeting the specification requirements. Mainly manifested in:

1, temporary electricity organization design is not standardized or not compiled.

(1) The organization design of temporary electricity consumption in some construction sites is not organized by professional electrical engineering technicians, but compiled by builders, safety officers or electricians, which can't be used to guide on-site construction at all. Some only write the scheme or the preparation, review and approval do not conform to the procedures.

(2) The compilation content is simple and the pertinence is not strong. The code stipulates that the organization design of temporary electricity consumption should include 8 items, but some items only have 2 ~ 3 items;

(1, field investigation;

(2) Determine the position and line direction of power supply incoming lines, substations or power distribution rooms, power distribution devices and electrical equipment.

(3) Load calculation.

(4) Select transformer

(5) Design of power distribution system (design of power distribution lines, selection of wires or cables, design of power distribution devices, selection of electrical appliances and design of grounding devices; Draw temporary electricity engineering drawings, mainly including the general plan of electricity engineering, distribution equipment layout, distribution system wiring diagram, grounding device design diagram)

(6) Design lightning protection device

(7), determine the protective measures

(8), formulate safety measures and electrical waterproof measures.

Some directly calculate electricity consumption without calculating the number of mechanical equipment, and the calculation results are unfounded; Some do not have overhead lines and external protection, but copy the provisions in the specification; Some temporary electricity organization designs still refer to JGJ 46-88.

2. Incomplete safety technical files

After the temporary electricity construction is completed, there is no acceptance certificate; There is no checklist during the operation; The electrician has no work record of installation, inspection, maintenance and disassembly; There is no record sheet for the measurement of 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.

In some construction sites, the distance between the external power lines and transformers and the scaffolding outside the building is less than the standard, or even some of them are located within the working radius of the tower, but there are no protective measures or the protective height is not enough, which not only has serious hidden dangers, but also is prone to electric shock accidents.

4, grounding and lightning protection is not standardized

It is strictly stipulated in the Code that "some equipment shall not be connected to zero protection and some equipment shall be grounded", but a few construction sites are still doing this, or the number of repeated grounding groups can not meet the requirements. It is stipulated in the specification that the protective zero line in TN system must be repeatedly grounded at the middle and end of the distribution system in addition to the distribution room or main distribution box, that is to say, the repeated grounding at the construction site shall not be less than three groups. However, a few construction sites only do a set of repeated grounding at the main distribution box, and some construction sites do repeated grounding at the switch box not with angle steel, steel pipe or smooth round steel, but with rebar.

5. Transformer room

It is stipulated in the specification that the power distribution room is close to the power supply and should be located in a place with less dust, humidity, vibration, corrosive media, flammable and explosive substances and smooth roads. During the supervision and inspection, it was found that some distribution boxes and general distribution boxes were not high enough, and it was easy to get water. There is no security fence around them, and there is no normal lighting and emergency lighting in the room.

6. Distribution lines

There are two ways to set up overhead lines and underground in the specification. For buried lines, the buried depth should not be less than 0.7m, and fine sand with a thickness of not less than 50mm should be evenly laid on the top, bottom, left and right sides of the cable, and then covered with hard protective layers such as bricks or concrete slabs. However, most construction sites can't do this, and some of them are buried in the ground, but the depth is very shallow, forming an open section and an underground section, and crossing without protection. It is easy to damage the cable sheath when people run over it. The mandatory standard stipulates: "Five-core cables must contain light blue and green/yellow insulated cores. Light blue core wire must be used as N wire; PE wires must use green/yellow core wires, and it is strictly forbidden to mix them. " In some construction sites, the green/yellow double-color core wire is used as N wire, which seriously violates the provisions of the code. There are also some unsafe factors such as wires and cables on the construction site being pulled and connected randomly, or being wound on steel pipes, or pressed under steel bars, and the packages are not tight. Unsafe factors such as the use of flower lines and glue lines on site and the failure to fix cables for tower cranes with porcelain bottles can be seen everywhere.

7, distribution box and switch box

The specification specifies the materials, specifications, dimensions, uses, installation positions and heights of the general distribution box, distribution box and switch box used in the construction site, and also specifies the electrical setting types of various electrical boxes. However, from the inspection of the construction site, it is far from the requirements of the specification. If some main distribution boxes, sub-distribution boxes and switch boxes are shipped from the last site, they are very worn out; Some are processed and produced by the project department itself, which is extremely irregular; Some of them were bought from the market, not registered in the safety supervision department, and did not reach 3C certification. In addition, the installation height of switch boxes in many construction sites and the distance from electrical equipment can not meet the specification requirements. Most mobile machines, such as cutting machines, vibrators and hand-held power tools, are not equipped with mobile switch boxes. The installation position of some switch boxes is not conducive to operation. There are many places where the distribution box and switch box are stacked with processed steel, square timber, templates, steel pipes and other items, which violates the regulations that there should be enough space and passages for two people to work at the same time around the distribution box and switch box, and articles that hinder operation and maintenance should not be stacked.

The electrical setting in the electrical box is illegal, such as the disconnector installed in the distribution box has no visible breakpoint. Some switch boxes are equipped with several plugs; Most of them are equipped with handle switches (such switches shall not be used in the construction site); Some only install leakage protectors, which can not meet the requirements of "one machine, one brake, one box and one leakage"; In some switch boxes, the order of leakage protector and disconnector 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.

8, electric construction machinery and hand-held power tools

The Code stipulates: "The metal shells of motors, high-voltage devices, electrical appliances, lighting appliances and hand-held power tools must be protected and connected to zero." In our daily supervision and inspection, we found that most of the places have not been done, including all kinds of steel processing machinery, woodworking saws, cutting machines and so on. In addition, the field dysprosium lamp and iodine tungsten lamp always use two-core cable, so it is impossible to connect the shell to zero. At present, in many construction sites, in addition to woodworking saws, most of them still use hand-held cutting machines on the operation surface. There is no switch box and only sockets are used for connection.

9, safety education and training and related certificates

The code stipulates that "electricians must pass the examination according to the current national standards before they can take up their posts with certificates", and also stipulates that "the level of electricians should be adapted to the difficulty and technical complexity of the project". Most electricians on the construction site can take up their posts with certificates, but there are still a few electricians who have not done so. There is also a problem here, that is, some electricians, especially those who are new to electrical work, lack technical knowledge and fail to study, understand and implement the specifications, which leads to a large number of hidden dangers in the temporary electricity use on the construction site, such as the configuration of various electrical boxes, the electrical installation and wire connection in the electrical boxes do not meet the requirements of the specifications, and the hidden dangers of accidents always occur repeatedly. After obtaining the work permit, electricians should not take part in safety training, education and physical examination once every two years as required. Some electricians did not participate in the review during the review period, and their certificates automatically became invalid. Many projects only pay attention to the distribution of laws, regulations, standards, rules and specifications on engineering quality, but do not pay attention to the distribution of laws, regulations, standards, regulations and specifications on safe production and civilized construction, including the Technical Specification for Temporary Electricity Safety on Construction Site (JGJ 46-

2005)。

In view of the above problems, the following solutions are proposed for reference:

1, seriously study, understand and implement the specification.

The project management department of the construction unit shall distribute the Technical Specification for Safety of Temporary Electricity Consumption on the Construction Site (JGJ 46-2005) to relevant personnel and electricians, and organize learning and understanding, especially electricians should be familiar with the contents of the specification and the provisions of mandatory standards, so that the temporary electricity consumption on the construction site can meet or basically meet the requirements of the specification, thus ensuring the safety of construction electricity consumption.

2, preparation and review should be strict.

The project management department of the construction unit shall, according to the characteristics and difficulty of the project undertaken, prepare the temporary electricity consumption organization design according to eight contents. The organization design of temporary electricity consumption should have the compilation basis and the principle of electricity consumption, and must be targeted and operable, and cannot copy the provisions of the specification. In addition, the supervision unit must be careful when reviewing the organization design of temporary electricity consumption submitted by the construction unit, and require the construction unit to rectify or re-compile it in time as a programmatic document for temporary electricity consumption construction to standardize the temporary electricity consumption behavior.

3. Improve the technical quality of electricians

In view of the current situation that the electrician's technical quality is low and it is difficult to meet the needs of temporary electricity construction on the construction site, the following requirements are put forward for electrician operators:

(1) Electricians should not only hold relevant certificates, but also have corresponding technical level. If the electrician is just engaged in this job, the project manager can recruit retired, unemployed and laid-off experienced old electricians from enterprises and bankrupt enterprises, and they will pass on, help and lead them.

(2) From the past electrician training, the textbook used is not the Technical Specification for Temporary Electricity Safety in Construction Sites (JGJ 46-2005), but the general basic knowledge of electricians. The training content can't be well connected with the requirements of temporary electricity consumption on the construction site. In the future, we should take JGJ 46-2005 as the main teaching material, and arrange at least one day for students to go to the construction site, so that they can visit both good and bad construction sites.

4, do a good job in temporary electricity management.

In addition to formulating measures for safe use of electricity in temporary electricity organization design, it is also necessary to formulate regulations for safe use of electricity in office areas, living areas and migrant workers' accommodation. Today, the electricity consumption of migrant workers' accommodation on the construction site is different from that in the past. At that time, there was only lighting in the room, and the electricity consumption was very small. Now, most migrant workers have mobile phones, and some have televisions. The electricity consumption has greatly increased. To this end, on the one hand, when building dormitories for migrant workers, we must consider the electricity consumption of the rooms and leave an appropriate amount of sockets for future needs. It should be further stipulated in the Regulations on the Administration of Safe Electricity Use that it is forbidden to use simple electric fans in summer, to use electric stoves (especially homemade electric stoves) and large lamps such as iodine tungsten lamp for heating in winter, and to use inferior electric blankets to prevent electrical fires. Electricians should strengthen inspections and immediately stop or confiscate electricity facilities if they find illegal electricity use, so as to ensure the safety of electricity use in living quarters.

Step 5 take protective measures

In engineering construction, most beams, columns and floors are cast-in-place reinforced concrete. Vibrators are frequently used, especially in the cast-in-place floor slab, and the power cord of the vibrator is dragged around the steel bar, which is easy to be scratched and causes leakage. In order to avoid this phenomenon, a 4 cm plastic water pipe can be wound around the power cord of the vibrator. The power line is 33 meters long and the working range is 60 meters, which can meet the construction needs. This can not only prevent the sheath of the power cord from being damaged, but also prolong the service life of the power cord and effectively prevent people from getting an electric shock.

6, earnestly implement the rectification.

It is suggested that the construction enterprise should conduct a safety inspection every half month, seriously organize the rectification of all kinds of hidden dangers found in the temporary electricity consumption on the construction site, and thoroughly treat those that do not meet the requirements of the specification to ensure that there are no dead ends and no future troubles.

7, clear responsibility system

It is clear that the professional electrician is the first person responsible for the temporary electricity use on the construction site. Electricians are responsible for the installation, maintenance, replacement and removal of temporary electricity. Without the permission of the electrician, other personnel (including the general contractor and the sub-contractor) shall not pull the wires without permission. Electricians should be given the right to punish. Once a labor service team or sub-team violates the rules, electricians have the right to impose economic penalties and confiscate electrical items. In addition, the relevant personnel of the project department (including electricians) can sign temporary electricity safety contracts with labor service companies and subcontracting teams, and use standardized terms to regulate the electricity consumption behavior of each unit. Only in this way can we manage the temporary electricity consumption in the construction site in an orderly way, which can not only ensure the normal electricity consumption in construction and life, but also effectively avoid the occurrence of electric shock accidents.