After China's reform and opening up, it introduced international standards and developed country standards. In 1988, China promulgated the "Standardization Law of the People's Republic of China", which stipulated the "National Encourage the Adoption of International Standards". During this period, some electrical engineering codes promulgated by China have cited some of the international electrical standards "IEC standards" to varying degrees. Safety requirements. The national standard GB50054-95 "Low-voltage power distribution design specification" is a standard that has done a good job in this respect. This is because the content it needs to stipulate is very compatible with the IE660364 "Building Electrical Installation" standard and can be cited in large numbers. This makes it significantly better than the previous version of GBJ54-83 "Low-Voltage Power Distribution Units and Circuit Design Specifications". Everyone knows that most electrical accidents occur in low-voltage electrical installations. The promulgation and implementation of this regulation is to promote the advancement of China's electrical safety technology. It has played a good role in reducing the occurrence of electrical accidents.
Due to the development of technology and the emergence of new electrical hazards, IEC standards and developed country standards are constantly being revised and supplemented. China's "Low-Voltage Power Distribution Design Specifications" is no exception, especially due to certain regulations in the year. There are inadequacies in the content of the specification and the limitations of the technical level. Due to the importance of this regulation, its modification and supplement is a concern of the majority of electrical workers in China. The author is one of the editors of the specification. I would like to throw a brick to attract jade and state some shallow opinions.
1. Get rid of the old technical concept, modify and supplement GB50054-95 according to IEC standards. Due to historical reasons, China's building electrical design guiding ideology is deeply influenced by the former Soviet Union's "Electrical Installation Procedures". This procedure is mainly prepared by the former Soviet power station department, while the former Soviet power station department's preparation procedures focus on the safety of electrical networks, that is, the safety of the grid lines, transformers, generators and other grid components; and IEC and some developed countries Building electrical installation standards emphasize the people-oriented principle. Emphasis on the safety of people and property. That is, the focus is on protecting against personal electric shocks, electric burns, electrical fires in buildings, and electrical equipment damage. The focus of the two is different. China's building electrical designers are deeply influenced by the regulations of the former Soviet Union. In the design, the protection of the line is often considered, which is obviously manifested in the chapter of the distribution line protection of GBJ54-83. This chapter only specifies short-circuit protection and overload protection to protect the line from damage, and does not mention a large number of other electrical safety requirements that cause personal accidents and property damage. This is inevitably inverted. The line can be worth a few, but human life is priceless, and the value and impact of the two are incomparable. In the following GB50054-95 quoted a number of electrical safety regulations of IEC60364, added a number of provisions to prevent grounding faults and personal shocks, the content is very substantial, but if it is similar to the IE060364 standard and developed countries Compared with the standard, it is not difficult to find that there are many blank points in electrical safety in GB50054-95. As far as the protection of the power distribution system is concerned, the protection requirements for overcurrent and ground faults are not perfect enough, such as the protection of faults such as undervoltage, overvoltage, and thermal effects, as well as the application requirements of commonly used important protective measures such as extra low voltage and loop isolation. Incorporated. The occurrence of these blank spots is subject to objective constraints at the time. Because the preparation of the specification at that time was only slightly modified on the basis of GBJ54-83, it could not be changed too much in the normative structure. However, the occurrence of electrical accidents is unrestricted. The identification and analysis of many electrical accidents in these years shows that quite a number of electrical accidents can not find the cause and preventive measures in China's regulations, but it is stipulated in IE660364 and developed country standards. It is clear that this is an important reason for the frequent occurrence of electrical disasters in China. In order to reduce electrical disasters, ensure the smooth development of the national economy and the happiness and stability of people's lives. It is necessary to timely remove the obsolete technical concept of building electrical design codes including GB50054-95. A comprehensive Modify the supplement.
It should be noted that the low-voltage electrical equipment includes the terminal circuit and the electrical equipment. This involves the national standard "General Power Equipment Power Distribution Design Specification" and other relevant specifications, which need to be properly arranged and organized by the relevant competent authorities. Safety requirements are fully reflected in China's regulations to avoid omissions, so as to avoid future hidden dangers in electrical design and installation.
2. Need to increase the electrical safety requirements of special places
Both IEC and developed countries have specific electrical safety standards for special places or devices with high electrical hazards. This reflects the importance attached to electrical safety. China's GB50054-95 is still blank in this respect, it only applies to general places without special requirements. In this way, the design of electrical installations in special places in China has no rules to follow. It is still designed and installed according to general places, because the protective measures are not comprehensive. The resulting electrical accidents sometimes occur. For example, in the previous year (1999), there was a tragic death of seven people in a fountain in Qingdao. Last year, there were many electric fires in the sauna in Beijing, one of which burned seven people. As for the electrical accidents in places such as bathrooms, street lamps, advertising lights and the like. It’s been heard. The lack of GB50054-95 in the special place electrical safety requirements chapter is a big shortcoming.
The electrical hazards of different special fields are different, and the preventive measures are not the same, and they cannot be applied. For example, the electrical danger of the bathroom is that the impedance of the human body is greatly reduced; the swimming pool also has this electrical hazard, but its location and bathroom are not the same; the electrical danger of the fountain is to allow 220V electrical equipment to enter the water. Each of these three has its own preventive measures and should be distinguished.
The electrical hazard of the sauna is that the high temperature causes the electrical insulation to drop, causing a short-circuit fire: the narrow conductive place is a metal object with a ground potential that is difficult to separate due to a large area, and the telephone accident is caused; the hospital operating room, especially the chest operating room is Strict equipotential and loop isolation requirements are imposed due to their severe potential difference limitations. Special places and devices such as these require electrical safety regulations, otherwise it will inevitably lead to various electrical accidents.
For the electrical hazards of special places and installations, you can't be suspicious, and you can't think that you need to improve your protection requirements in foreign or high-end places. It is not necessary in China or low-grade places. Because electrical dangers are regardless of national race, no matter how high or low, and everyone has the right to survive. In the specification, it is necessary to make provisions, and it should not be too troublesome to implement, and the follow-up will be taken lightly.
3. In the current GB50054-95, the provisions and standards that need to be considered are all enriched and improved in the continuous modification and supplement. GB50054-95 will inevitably be revised and supplemented. The author will understand the following, and some of the obvious GB50054-95 are worthy of discussion and simple examples for reference.
(1) Electrical safety refers to personal safety and property safety. However, in general, 1.0.1 only guarantees personal safety and does not mention property safety. Some sections of GB50054-95 are not sufficient for China's very serious electrical fires. It may be related to the guiding ideology of neglecting property safety during preparation.
(2) According to the IEO standard, the AC low voltage refers to the voltage of 1000V and below. The 1.0.2 will stipulate the voltage of AC below 500V. It is obviously inconsistent with the low voltage range of the IEC standard and the general concept.
(3) 2.1.3 2.1.7 is the isolation requirement for the live conductors to ensure that the maintenance personnel are protected from electric shock during electrical maintenance, but it is not specified. As a result, the implementation of the provisions is not understood by everyone. As a result, China has appeared. Abuse of the four-pole switch. A description of the intent of the provision should be appropriately supplemented to guide the proper implementation of the provision.
In addition, the Circuit Breaker that satisfies the isolation requirement can also serve as an isolation device. The point that the fuse cannot be used to isolate the neutral line is also to be supplemented in the article.
(4) The allowable minimum core section of the loop protection line needs to meet both the mechanical strength and the thermal stability of the short-circuit fault, while the cable and sheathed wire do not require the minimum cross-section according to the mechanical strength. The provision of the minimum cross-section of 2.1.32.1.7 does not provide sufficient clarity and completeness for these requirements, and it is not easy for the performer to have a clear and comprehensive understanding.
(5) The requirement that the PEN line is prohibited from accessing the switchgear in 2.2.1 is not the content of the conductor selection. It shall be repeated in the following paragraph 4.5.6 and shall be deleted.
(6) For power distribution systems with only long delay, short delay and transient overcurrent functions, it is sometimes difficult to fully guarantee the selectivity of interstage protection. Therefore, 4.1.2 stipulates that “for non-importance Load protection appliances. Non-selective cut-off can be used.†However, due to technological advances, inter-stage selective interlocking technology (ZSI) has been widely used in low- and medium-voltage systems to ensure inter-stage selection of important loads. 1, life, China has introduced this technology, whether it needs to keep up with the progress of technology in 4.1.2.
(7) The TN-C part of the TN-C system and the TN-C-S system cannot be equipped with RCD, and only the zero-sequence protection with low sensitivity is used for ground fault protection. The intent of the second paragraph of 4.4.10 is here, but the term “three-phase four-wire system†is incorrect. It should be changed to “TN-C system and TN-C part of TN-CS systemâ€.
(8) The leakage current action protector in 4.4.11 should be changed to “residual current action protector†or “RCD†(the same below), because the term “leakage current action protector†has been stopped in the product standard.
(9) The value of I â–³ n in fire protection RCD in 4.4.21 “should not exceed 0.5A†should be changed to “not more than 0.5Aâ€. Because 0.5A is only the minimum current that the grounding arc current energy can ignite, the grounding arc current is generally greater than 0.5A. Therefore, unless there is a special requirement, the value of I Δ n is not limited by 0.5A. The 1â–³n values ​​in the IEC product standard and the IEC60364 standard example are greater than 0.5A, up to 20A.
In addition, this article does not make it clear that this fireproof RCD (actually a Circuit breaker with residual current action protection function) should be installed at the power inlet of the building to prevent grounding arc fires throughout the building (this is for TT) The system is especially important), and it is not clear whether the RCD is three-phase or single-phase. The three-phase RCD detects the vector sum and non-algebraic sum of the three-phase leakage current of the whole building, that is, the three-phase leakage current cancels each other instead of superimposing, so unless the wiring is incorrectly installed, the three-phase RCD is very difficult. Misplaced. It should be specified and clearly stated in the article to avoid the misunderstanding of the safety measures of this important anti-electrical fire in China.
(10) The provisions of Article 4.5.4 regarding the installation location of overcurrent protection appliances are technically correct. However, the words used in the text do not seem to be coordinated with other provisions, and may be subject to the US Electrical Code (NEC) idioms. reason. For example, in the article, "the phases that are not grounded" are actually "phases" because they are not grounded in China; for example, "three-phase three-wire power distribution system in which the neutral point is not grounded and the N line is not led out", The actual is "not to mention the neutral line, Ding system", the article read is puzzling. It should be concisely expressed in terms of IEC for easy understanding and consistent with the terms of other provisions.
(11) 4.5.5 and 4.5.6 are intended to reduce the “zero-break†accident of the three-phase four-wire system, and it is stipulated that the provisions of the switch contacts are not required to be installed on the neutral line in order to prevent overcurrent of the neutral line. The overcurrent of the line is only related to the live conductor system and not to the grounding system. This is true for TT and TN-S systems, as well as for other grounding systems. Therefore, it is not appropriate to stipulate that this requirement applies only to TT and TN-S systems. It should be deleted.
(12) In the electrical installation of the building, the PEN line is not allowed to be disconnected with the switch contacts. This is true for the PEN line in the TN-C system. This is also true for the PEN line in the TN-C-S system. The PEN line does not appear in other grounding systems. Therefore, it is not appropriate to specify this requirement in Section 4.5.6 as only applicable to the TN-C system. It should be deleted.
4. Building electrical equipment -it specifications should be equivalent or equivalent, EC standards, should not "close" IEC standards including GB50054-95 electrical design specifications related to the lives and property of thousands of people. The impact of a design error is only partial, and the normative error is harmful to the whole country. The responsibilities of the standard compilers are small and the responsibilities are very large. The standardization work should be concerned and supported by the majority of electrical counterparts.
Due to various reasons, there is a certain gap between China's building electrical level and developed countries. This is also reflected in the level of China's building electrical codes, and there are many problems in the building electrical design specifications. But compared to the past, there are now - very good conditions, that is, a relatively complete set of IEC building electrical equipment standards can now be used as the basis for the preparation of building electrical design specifications. The IEC standard is a lesson learned from many years of numerous electrical accidents in many countries. It is a valuable intellectual wealth shared by the international community. We should make full use of this wealth in the normative preparation. The IEC standard should be adopted in accordance with the provisions of China's Standardization Law to prepare China's building electrical design specifications. Some developed countries have done exactly that. China needs to do this after China's accession to the WTO, because it is conducive to communication and consistency with foreign electrical safety requirements.
It should be noted that the EC standard should be used instead of or equivalently, instead of “close†the IEC standard. Some of the current norms seem to be contradictory to each other. In fact, violations of the EC standards can also be vaguely referred to as "close" IEC standards. Because the word "close" is not defined. The scalability is very difficult to scale.
China's building electrical design codes lack authority in the international arena. It has not even been recognized by Hong Kong, which has returned to the motherland. This is only a temporary backward. Under the efforts of China's construction electrical counterparts, this backward situation can certainly be reversed. It is believed that the days when China's building electrical design codes are universally adopted by countries and become internationally authoritative norms will come soon.
Source of information: Excerpt from 2005.1 "Electronic Information Express"
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