Several problems that should be paid attention to

Several problems that should be paid attention to in the organization design of temporary electricity use on the construction site

since the implementation of the technical code for safety of temporary electricity use on the construction site (JGJ) issued by the Ministry in 1988, the management level of temporary electricity use on the construction site of our company has been continuously improved, and the organization design of temporary electricity use has been developed from scratch, from coarse to fine. The inspection and supervision after the electricity use management has been changed to the prevention and control in advance, and a certain effect has been achieved. However, I have been engaged in the review of "temporary electricity design" of project engineering for many years, which greatly limits its scope of application. I often encounter several problems in "temporary electricity design" that are not well considered and poorly targeted. Now I summarize them as follows:

1 Load calculation:

(1) the total load demand on the construction site can generally be calculated according to the formula, but the load calculation of each branch (from the main box to each sub box) is not paid enough attention to, and the calculation is incomplete. The amount of branch load calculation is extensive, and whether the calculation is correct or not will directly affect the quality and safety of power supply operation. For trunk wiring, it should be calculated in sections, and for radial wiring, it should calculate the load in circuits

(2) the allowable voltage drop of the line is not checked. Especially when the high-power equipment is put into operation, it has a great impact on the voltage at the end of the line. When the allowable voltage drop exceeds the specified range, it may cause the equipment to not be put into use due to undervoltage, or even burn the electrical lines and equipment, and then fire and personal safety accidents will occur. Last year, our company constructed a project in Fuzhou. In the early stage of construction, because the new transformer was not installed in place, the construction site used a transformer on the original site to supply power. Because the power supply was more than 300 m away from the distribution box on the construction site, when the 100kVA butt welding machine was put into use, the line voltage plummeted, and many leakage protectors tripped due to undervoltage, affecting the normal operation of other equipment. After finding out the cause, the problem was solved by setting up a separate cable in the butt welding machine circuit and increasing the cross-section of the power supply line conductor

(3) the foundation and upper construction belong to different construction periods, and the equipment loads of some projects are not calculated separately, which should be paid attention to in the audit

2. In terms of high-rise buildings and cross construction operations: the construction power consumption and cross construction operations of the basement, high-rise floor, roof and other "heaven to earth" parts were not seriously considered. The "temporary power design" did not draw the elevation trunk line diagram, and the local lighting of staircases, unloading platforms and other places did not adopt safe voltage power supply, and the waterproof and rainproof measures of electrical appliances and unified caliber were formulated. During the peak period of construction, when there are cross operations of multiple types of work and multiple subcontractors, the "temporary power design" does not reserve electrical circuits, and the phenomenon of "grabbing and spider" often occurs in line erection

3. Design of box size and drawing of electrical appliance installation wiring diagram: some projects "temporary power design" are divorced from reality, and there are too many sub box circuit designs, resulting in too large box size, large single processing cost, and difficult movement, which are not welcomed by the construction site. At this time, the project department casually purchased empty electrical boxes and electrical appliances to install them by itself, and the quality cannot be guaranteed. At present, the electrical boxes used in our construction site are "finalized" products from some qualified manufacturers. Except for special requirements that require additional electrical drawings, the circuit design of the "temporary power design" electrical box generally applies the "finalized" product electrical drawings, which is easy to be accepted by the project department

4. Estimation of power capacity: Although the power consumption of each project is different, a comparison can be made in the review of "temporary power design" of similar projects, and unnecessary waste can not be caused by the practice of "the larger the power capacity, the safer". If the power supply (capacity) has been determined by the construction unit before the commencement of the project, only capacity calibration will be carried out after load calculation. Some engineering projects in the rush period should also be prepared to consider self-contained power supply. Based on the analysis of the "temporary power design" data of hundreds of medium and high-rise residential projects I have reviewed, the temporary power load demand on the construction site is close to 10va/m ＜ sup ＞ 2 ＜/sup ＞ (building area). When the design capacity is too large, we should carefully check the number of equipment and the selection of systems, so as to improve the efficiency and accuracy of the review

5. Statistics of the number (capacity) of construction equipment: the planned equipment required in some "temporary power design" is inconsistent with the number (capacity) of equipment in the construction organization design of the project, and there is a large difference, which is caused by the different personnel and time of preparation, and there is no communication and proofreading. The number (capacity) of equipment in the construction organization design of some individual projects is compiled by "beating the head", which is simply unrealistic, and such "temporary power design" has lost its guiding significance

6. Non electrical professional technicians prepare "temporary power design": the "temporary power design" at the construction site requires the preparation of review report before the commencement of the project. However, due to the lag of some electrical technicians of the project department, the "temporary power design" is handled by non electrical personnel copying the data of other project projects from the computer

7. Formulation of technical measures for safe use of electricity and electrical fire prevention measures:

some electrical professionals did not prepare targeted measures for safe use of electricity and electrical fire prevention according to the characteristics of their project, but copied the code for temporary electricity section by section. There is no mention of the protective measures for external power lines, the protective methods for the lines entering the buildings, the requirements for the erection of electrical lines in migrant workers' dormitories, the selection of installation positions of electric boxes (especially the laying of vertical trunk lines in high-rise buildings), the fixing methods, rain proof and waterproof measures for mobile electric boxes, and the practices of grounding devices

8. Investigation on the protection mode of electrical equipment (off-site) and underground pipeline layout of the same power supply system: in the on-site exploration content of "temporary power design", everyone pays more attention to whether there are external power lines around the construction site and whether the lines reach a safe distance from the projects under construction. However, the layout of underground pipelines and the sharing of the same power supply system between equipment and external power lines at the construction site are often not investigated in detail, and there is no exact written data, resulting in wrong judgment. As a result, some equipment in the same power supply system adopts protective grounding, and the other part 6) orthoclase 7) quartz 8) Topaz 9) corundum 10) diamond protective neutral connection, which does not meet the requirements of safe power consumption; Once an accident occurs, it is difficult to distinguish

9. Setting of power distribution room: is it necessary to set power distribution room at the construction site? With the power distribution room, there must be the requirements of "five prevention and one connection", as well as the requirements of Chapter V of the code for temporary electricity, "the operation channel is not less than 1.5m", "the maintenance channel is not less than 0.8m", "the ceiling is not less than 3M from the ground", "the fire resistance rating of buildings and structures is not less than grade 3", etc. I remember that in the 1990s, the magazine building safety reported that at that time, the national construction site temporary electricity seminar was held in Shanghai. The meeting elaborated that whether to set up a power distribution room on the construction site should be determined according to the actual power load on the site, and there was no exact quantitative boundary. Some "not too big and not too small" projects recently avoided the setting of the distribution room when preparing the "temporary power design", resulting in tossing and turning in the approval, which was inefficient. In 2002, our company made a regulation: if the calculated capacity of temporary electricity on the construction site is 100kVA or above, the distribution room shall be set up in accordance with the requirements of the code for temporary electricity. It shall be implemented as a system of the construction site power management of the head office (as one of the on-site review contents of the commencement report)

"temporary power design" is one of the special safety organization design contents with strong professionalism. It is suggested that all units establish computer document templates by themselves, hoping to help everyone standardize management, improve efficiency, and reduce design errors and omissions

with the continuous efforts of everyone, the "temporary power design" of the construction site will be closer to reality, guide the site and improve the overall power management level. Limited by the level, the above issues are for reference only