At the second session of the Fifth Standing Council of the Provincial Civil Engineering Society, the Electrical Professional Committee organized all standing committee members to study the provisions in depth and communicated about common problems and problems that violated the "Articles" discovered during the review work in various places. , and also expressed their opinions and heated discussions on controversial issues to achieve preliminary understanding. Recently, the Fuzhou area executive directors and some examiners once again exchanged opinions at a small-scale meeting. Everyone agreed that it is necessary to publish the collected common problems that violate the "provisions" in the construction drawing review, so as to serve as a warning and enable similar people to do so. Mistakes are not repeated. I have analyzed, summarized, organized and combined my own experience in review work on common issues as follows. Due to the limitation of level and space, I will not go into too much detail. I will just highlight them. Any deficiencies in them only represent my personal opinions. , corrections welcome.
(1) The issue of "the classification of electric power load" (Article 2.0.1 of "Provisions" GB50052-95)
1. The design document should describe the building area , height, purpose and determine its nature, fire protection category and electrical load level; it should not just generally state that the entire building is designed according to a certain level of load, but should provide a hierarchical description of each electrical load.
2. Load classification errors, common ones include: (1) For department buildings with a height of less than 24m and an area of ??more than 3000m2 per floor, exhibition buildings and public buildings with outdoor firefighting water consumption exceeding 25L/S*** architecture. "Code for Fire Protection Design of Buildings" GBJ16-87 stipulates that the fire-fighting electrical equipment shall be powered as a second-level load. The designer did not search for relevant specifications or communicate with the construction and water supply and drainage professionals. He thought it was a low-rise building and blindly determined it to be a third-level load. ; (2) The same specification stipulates that the fire-fighting power load of factories and warehouses with outdoor fire-fighting water consumption exceeding 30L/S should be Level 2, but it is mistakenly designated as Level 3 load; (3) Kitchen power and cold storage in first- and second-level hotels It belongs to the first-level load, but it is designed according to the third-level load; (4) For high-rise first- and second-level buildings, it is customary to use a height of 50 meters to classify them, without paying attention to their use and nature. For example, for 8-story buildings with a height of 32 meters A hospital, or a comprehensive building with an area of ??more than 1000m2 per floor and a height of 28 meters belongs to the first category of high-rise buildings. Its fire protection electrical load should be Level 1 but is classified as Level 2, etc.
(2) Regarding the power supply of the primary load (GB50052-95 Section 2.0.2)
1. The "Articles" stipulate that the primary load should be powered by two power sources. Designers generally know this well. The main problem lies in the lack of simultaneous design or "separate commission" of many engineering substations and distribution stations. Some areas simply stipulate that all substations 10KV and below are designed by the power supply department, even the interiors of high-rise buildings. For substations, only spaces are reserved. This is an abnormal practice and may lead to many potential violations of the "articles". In this case, the designer should put forward clear technical requirements for the power supply level. If only the terminal design is done, the entrusted party will blindly follow the conventional system design and fail to meet the load level requirements. A relatively good approach can be to provide the main wiring mode of the power supply and distribution system supplemented by instructions on the operation mode, or to classify each circuit in a list according to load level and power supply requirements.
2. For Class I high-rise buildings, when a diesel generator is selected as the second power source for the primary load, the design should clearly require that the diesel generator be equipped with a self-starting device and be able to supply power within 30 seconds. Only in this way can we meet the "high regulations" requirements for fire protection design to be powered by first-class power supply.
3. When the two power supplies of a Category 1 high-rise building are drawn from two feeders of a nearby switching station, it should be made clear that the two power supplies at the upper level of the switching station come from two different power plants or from two regional substation.
(3) Regarding the issue of "parallel measures to prevent errors must be taken between emergency power supply and normal power supply". ("Provisions" GB50052-95 Article 3.0.2)
1. The design document should include relevant instructions on the measures to prevent errors and the design content of the drawings.
2. The design should not simply state that "parallel measures to prevent errors should be taken". For primary loads, special attention should be paid to expressing the self-starting conditions of the diesel generator, and the electrical and mechanical connections between the main switches. Lock conditions, as well as the accessories that the main switch must be equipped with, and the interlocking relationship between key switches for mechanical interlocking should be given.
3. According to the interpretation of the "Articles", the self-starting signal of the diesel generator should be taken from the auxiliary contact of the main switch of the normal power supply, and should not be taken only from the failure of the secondary circuit of the high-voltage side incoming voltage transformer. Pressure signal.
(4) Issues with the layout of power distribution devices (Article 4.2.6 of the "Articles" GB50053-94)
1. The "Articles" stipulate that "the length of the power distribution device is greater than 6m "The passage behind the cabinet (screen) should be equipped with two exits." The violation mostly occurs when the transformer and low-voltage cabinet are combined (or there is a gap between them, but it is less than the width of one exit). There is also a misunderstanding that the " "Articles" only refers to low-voltage power distribution devices. It is ignored that the "Articles" also apply to 10KV power distribution devices. In large projects where the high-voltage cabinets have a large area and are tight, violations often occur.
2. For long power distribution rooms, two or more large-capacity transformers and power distribution cabinets are arranged in a straight combination, plus emergency busbar cabinets. The length is often more than 15m, and the passage behind the screen In addition to the two exits, a third exit should be added.
(5) "About the layout location of strong and weak current rooms". (JGJ37-87 "Civil Building Design Guidelines" Article 4.7.1)
Designers will generally pay attention not to arrange the power substation and distribution room directly below the toilet, bathroom, and washroom, but they should also pay attention Other strong and weak current rooms, such as diesel generator rooms, ring network cabinets, switch rooms, communication rooms, computer rooms, fire control centers, and strong and weak current distribution rooms reserved for the power supply department all have moisture-proof requirements. The rooms cannot be arranged directly below the kitchen, bathroom, or washroom.
In addition, the popularity of unit-type high-rise residential buildings in recent years has brought a difficult problem to the two majors of architecture and electrical engineering, that is, Article 6.2.5 of the "Articles" GB50045-95 (1997 edition) stipulates "Stairwells" "Except for the evacuation door leading to the corridor of the corridor, other doors, windows, and openings should not be opened on the inner wall of the front room of the smoke-proof staircase." Since maintenance doors need to be opened between strong and weak electric shafts, they should not be opened. It is allowed to be arranged in these parts, which will cause "violation" in the construction profession. This problem still needs the electrical profession to cooperate with the construction profession to come up with a comprehensive solution.
(6) "About the TN-C system, PEN lines are strictly prohibited from being connected to switching equipment" (GB50054-95 Article 2.2.12)
This "provision" is illegal This mostly occurs when the power supply of the TN-C-S system enters the home. Because some designers do not have a clear concept of the TN-C-S system, when a 4-pole entry switch is used, the repeated grounding point of the PEN line is taken after the switch. As a result, the PEN line is connected to the switchgear, resulting in a violation of the "Articles". This problem is often accompanied by a problem that does not comply with relevant professional standards. That is, when a 4-pole leakage switch is used for the power switch entering the building, the multi-line drawing method is to treat the PEN line as the neutral line, connect it to the N pole of the switch and pass it through. After passing through the leakage switch, the grounding is repeated. The result does not comply with the provisions of GB50054-95 Article 4.4.17 "PE or PEN wires are strictly prohibited from passing through the magnetic circuit of the current transformer in the leakage action protector", causing the leakage switch to malfunction. Correct The connection method should be to connect the incoming PEN line to the PE ground terminal (this terminal is connected to the ground grid or MEB). After completing the repeated grounding, separate the PE and N lines, and then connect the N line to the N pole of the four-level switch. Use single-line notation and should also use text to clearly express the repeated grounding before the switch.
(7) Regarding "When installing a leakage switch, it should be able to disconnect all live conductors of the circuit it protects..." ("Provisions" GB50054-95 Article 4.5.6)
The leakage circuit breaker installed in the single-phase socket circuit should be bipolar (2P or P N). The leakage circuit breaker installed in the main switch of the residential building to prevent electrical fire should be level 4 (4P or 3P N). , since most civil buildings have single-phase loads, the three-phase loads cannot be completely balanced, and the N line is a live conductor. If the N line cannot be guaranteed to be at ground potential, the circuit breaker must disconnect it from the phase line at the same time for safety. The number of poles should be indicated on the distribution system diagram.
(8) Regarding the issue of fire protection and sealing of high-rise civil buildings (GB50045-95 (97 edition) Article 5.3.3)
The design instructions should require strong and weak current shafts to be installed in the equipment After completion, non-combustible materials equivalent to the fire resistance limit of the floor should be used as fireproof partitions on the floor. The gaps connected to rooms, walkways, etc. should be filled with non-combustible materials. Some designs have no instructions, or even though they have instructions, they are incomplete.
(9) "About the general equipotential bonding" issue ("Provisions" GB50054-95 Article 4.4.4)
The design document cannot simply say "the general equipotential bonding should be done" "Equipotential bonding" should be put forward based on the actual situation of the project, and the ground plane should also be expressed in place. It is good to follow the practice on page 7 of the national standard atlas 97SD567 "Equipotential Bonding Installation", but for large projects, it is necessary to start from the total equipotential terminal The galvanized flat steel box (MEB) is pre-embedded to each connection object. In actual construction, it is difficult to accurately place it in place at one time (because the location of the relevant equipment is not necessarily certain). I think it can be done in the substation of a large project or the power supply of a building. There is a "MEB" at the line box. For the sake of reliability, the "MEB" must be connected to the grounding grid at two points. The main steel bars in the ground beam connected to the "MEB" can be reliably welded to each other and lead to each grounding embedded block. Or steel bar taps, the effect can be seen as the same as the national standard, atlas practice, this can save labor and materials, and the steel bars are hidden in the concrete foundation beam and are not easy to rust, ensuring reliability. The terminals reserved by MEB can be used for connecting or making connections at adjacent connection points. Reserve.
It must also be reminded that many high-rise building HVAC and water supply and drainage shafts should also reserve general equipotential connection points, which also serve as lightning protection grounding.
(10) Regarding lightning protection issues ("Articles" GB50057-94, Article 2.0.1, 3.1.1, 3.3.10, 5.2.1)
1. Many projects do not specify the number of buildings. Lightning protection category.
2. For projects that may fall between Category 2 and Category 3 lightning protection buildings, such as large-area multi-story public buildings or commercial and residential buildings. , the "annual expected number of lightning strikes" should be carefully calculated to determine the lightning protection category of the project based on the calculation results and specification requirements. We should not arbitrarily design lightning protection buildings according to the three categories based on our feelings. Some single-story buildings may not even be designed without calculation. Lightning protection design may cause "violations"
3. The "Articles" require that various types of lightning protection buildings should take measures to prevent lightning wave intrusion. The specific requirements should be based on the various types of lightning protection measures in the specifications. Implementation, some projects use low-voltage overhead incoming lines, and the design does not require "installing a lightning arrester at the entrance and connecting it with the insulator iron feet and hardware to the grounding device of the electrical equipment"; use armored cables (including static electricity, For control and other system cables), there is no requirement that "the cable metal sheath, steel pipe, etc. be connected to the ground of the electrical equipment at the incoming and outgoing wire ends", which is a violation of the "Articles". In addition, attention should be paid to preventing the intrusion of high-level lightning waves and fixing them. For electrical equipment in the open air on the roof, such as cooling tower motors, aviation obstruction lights, roof floodlights, positive pressure fans, exhaust machines, etc., corresponding measures should be taken for the distribution lines. For details, see GB50057-94 Section 3.5 .4 regulations.
4. In the design of side lightning protection measures for Class II lightning-protected buildings, a considerable number of designers still use the provisions in the "Electrical Design Code for Civil Buildings" that "every day above 30 meters" The third floor is equipped with a voltage equalizing ring...etc." and the provisions of Article 3.3.10 of the "Articles" were not correctly implemented.
In particular, the fourth paragraph is "The top and bottom ends of vertically laid metal pipes and metal objects are connected to lightning protection devices."
5. The new and old specifications for the roof lightning protection grid as an air-termination device are different. The new specification is GB50057-94. For example, the requirements for Class II lightning protection buildings are ≤10×10m or 8×12m, while The "Electrical Design Code for Civil Buildings" is 15×15m, which should be paid attention to when designing.
(11) Regarding the specificity of elevator power supply (Articles 2.0.1 and 2.0.3 of "Articles" GBJ50182-93)
1. In order to ensure the safe operation of the elevator, To avoid interference from other electrical equipment, the "Articles" emphasize that "the elevator power supply should be dedicated and should be sent directly from the building's power distribution room to the machine room." That is to say, the power supply line should not carry other loads. In some projects, the elevator power distribution box is equipped with power supply circuits such as positive pressure fans, voltage stabilizing pumps, elevator machine room lighting, sockets, elevator shaft lighting, aviation obstruction lights, exhaust fans, etc., which violates Article 2.0.1 of the "Articles" , and also violated the provisions of Article 2.0.3 of the "Articles" which "separate the lighting power supply of the machine room and the power supply of the elevator". At the same time, it does not comply with the provisions of Article 9.1.3 of the "High Regulation" GB50045-95 that "fire-fighting electrical equipment should use a dedicated power supply circuit", nor does it comply with Article 2.0.9 of GBJ50182-93 that "the hoistway lighting should be provided by "Computer room lighting circuit acquisition" regulations. According to the "explanation of the provisions", "the lighting of the computer room should belong to the lighting of the building", so the design can consider setting up a lighting box in the computer room to distribute power to the computer room lighting, sockets, shaft lighting, etc. The power supply for high-rise buildings can be provided from the emergency lighting box, and for multi-story buildings, the circuit should be distributed from the power supply box on the floor.
2. Some designs place the elevator power box deep in the machine room, which violates Article 2.0.5.3 of the "Articles" regarding "the location of the main switch should be easily and quickly accessible from the entrance of the machine room."
3. The design should understand the maximum load current of the elevator (provided by the equipment manufacturer's sample), and correctly select the main switch. Special attention should be paid to when using a knife fusion switch, the melt current should be able to avoid frequent starts of the elevator. spike current. When using an air switch, you should choose a switch with electric motor protection characteristics. Some designs that use switches with lighting protection features or choose fuse melts based on the long-delay current value of the air circuit breaker violate the provisions of Article 2.0.5.1.
(12) Regarding illumination standard issues ("Articles" GBJ133-90 Articles 2.2.1 and 2.2.2)
Most of the violations found during the review are For the lighting of office buildings and reading rooms, since the lighting of offices and conference rooms is often designed in one go, the illumination standards are included in the "provisions", which stipulate that the minimum is 100LX. However, many designers are too arbitrary and arrange a few fluorescent lamps at will. It's too bad, it's far from the minimum standard of 100LX. In addition, the illumination of the reading room in the school's library did not reach the minimum standard of 150LX stipulated in the "Articles". By the way, although school lighting is not included in the "provisions", the illumination standards of school classrooms, computer classrooms and other places should meet the minimum standards of the corresponding regulations, and sufficient attention should be paid.
(13) Regarding fire protection design
Regarding fire protection design, in addition to the locations where automatic fire alarm devices should be installed as specified in the "high regulations" and "low regulations", as well as the necessary evacuation settings Except for the inclusion of emergency lighting parts in the "Articles", there are relatively few other contents, so there are relatively few problems that violate the "Articles". However, there are still many problems that violate relevant professional standards, so I will not go into details in this article.
What must be paid great attention now is the "Design Code for Automatic Sprinkler Systems" which was promulgated on April 5, 2001 and came into effect on July 1, 2001. Articles 6.2.7, 6.3.3, 11.0.1-11.0.5 of the GB50084-2001 edition are all mandatory provisions related to the electrical profession. Compared with the 1987 edition of the same specification and the "Design Specification for Automatic Fire Alarm Systems" GB50116-98, these "articles" propose a series of new, stricter and more specific regulations.
Since these "provisions" appear in the water professional specifications, designers of a considerable number of design units have not noticed them, or have not understood and implemented them properly, which has become a common and prominent problem of recent violations of the "provisions". Its main manifestations are: (1) The pressure switch of the wet alarm valve (or the pressure switch of the deluge valve group of the spray system when it is also used as a spray pump) is not implemented, and its action signal is directly led to the pump power box or the linkage cabinet of the fire control center with a solid line The chain automatically starts the sprinkler (fog) pump; (2) the fire control center does not realize the monitoring of the water level of the fire pool and the fire water level of the roof fire water tank (note that it refers to the high water level, that is, the water consumption for fire protection should be guaranteed); (3) Should Realize the fire control center's monitoring of the main and backup power supplies of the spray pump; (4) When used as a spray pump, the control and status feedback of the solenoid valves of the deluge valve group in the fire control center and the water pump room are not implemented. ; (5) The fire alarm system does not monitor the status of the inlet and outlet signal valves of the wet alarm valve. The design of these contents involves the wiring diagram of the water pump control principle of strong electricity, the fire alarm and linkage system diagram, and the fire protection floor plan. The design should be closely coordinated with the water major. However, many design units only issue a simple design after receiving the review report. Text modification notices cannot meet the design depth requirements. The above issues remind us that we must pay close attention to the information on the newly released "mandatory provisions", and at the same time, do not ignore the content related to the electrical profession in the relevant professional "provisions".
Summary:
The review of construction drawings also revealed that some people in our design team have insufficient awareness of learning and implementing specifications; some even have unclear basic concepts of the majors and have only a partial understanding of them; Some have a weak sense of responsibility and are full of errors and omissions; of course, objectively, some also have a design cycle that is too short and the drawings are produced in a hurry... However, it should be noted that construction drawing review has become a necessary procedure for basic buildings. It is different from the previous annual inspection of design quality. It cannot be left to chance and every designer must face it seriously. Although the current focus of the review is on violations of "mandatory provisions", the above listed are only "common diseases" and also involve related professional normative issues and serious design depth issues. Since it is "peer review, peer review", this cannot help but cause great shock and pressure to the designers. While everyone is complaining that "design is getting more and more difficult to do," we will be pleased to find that designers and reviewers are paying more attention to normative learning, research, and communication than ever before. The problem of violating "mandatory provisions" during review is gradually increasing. reduce. Although there are differences in the standards for grasping the standards due to the level of the examiners themselves, and also due to the "lag" of some standards themselves, which will cause controversy on some issues, this is still unavoidable in the near future, but in a sense it is also a matter of A good thing, it promotes a good academic atmosphere of learning, research, discussion and even debate in the design community. The opinions I expressed above may also be inappropriate or even fallacious. I only want to serve as a starting point, hoping to trigger a wider upsurge of learning and discussion, so as to achieve the goal of common improvement.
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