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 stipulates the provisions of the state that encourage the adoption of international standards. During this period, some electrical engineering codes promulgated by China have cited some safety requirements of the International Electrotechnical Standard "IEC Standard" to varying degrees. . 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 IEC60364 "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 has played a good role in promoting the progress of China's electrical safety technology and 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. As one of the editors of the specification, the author is willing 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 standard
Due to historical reasons, China's architectural electrical design guiding ideology was deeply influenced by the former Soviet Union's "Electrical Installation Installation Regulations". 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, emphasizing the safety of people and property, that is, focusing on the prevention of personal electric shock, electrical burns and electrical fires in buildings, as well as damage to electrical equipment. 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 geometric, and human life is priceless, 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 IEC60364 standard and developed countries Compared with the standard, it is not difficult to find that GB50054-95 still has many blank points in electrical safety. As far as the protection of the power distribution system is concerned, the protection requirements for overcurrent and ground faults are not perfect, such as the protection of faults such as undervoltage, overvoltage, and thermal effects, and the application requirements of common important protection 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 cannot find reasons and preventive measures in China's regulations, but they are stipulated in IEC60364 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 effects of outdated old technical concepts on building electrical design codes including GB50054-95, and conduct 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 to make the relevant electrical standards of the IEC standard. 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 developed specific electrical safety standards for special places or devices with high electrical hazards, reflecting the high 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, and it is still designed and installed according to general places. Because of the incomplete protective measures, electrical accidents caused by this happen. 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 installations, 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; 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 danger is 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, leaving hidden dangers.
3 The current provisions of GB50054-95, which need to be considered, are enriched and improved in the continuous revision 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 a few examples for future 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, and may be related to the guiding ideology of neglecting property safety during preparation.
(2) According to the IEC standard, AC low voltage refers to voltages of 1000V and below, while 1.0.2 limits the applicable voltage to AC voltages below 500V, which is obviously inconsistent with the low voltage range of IEC standards and general concepts.
(3) The provisions of 2.1.3~2.1.7 are for the isolation of live conductors to ensure that maintenance personnel are protected from electric shock during electrical maintenance, but have not specified them in detail, resulting in different understandings in the implementation of the provisions, resulting in the emergence of our country. The 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 double as the isolation electrical appliance, and the point that the fuse can not be used to isolate the neutral line and the like should also 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. It is not easy to make clear and complete understanding of these requirements by specifying the minimum cross-sections of 2.1.3 to 2.1.7.
(5) The requirement that the PEN line is strictly prohibited from accessing the switchgear in 2.2.1 is not the content of the conductor selection, and is repeated with the subsequent paragraph 4.5.6 and should be deleted.
(6) For distribution systems with only long delay, short delay and transient overcurrent functions, it is sometimes difficult to fully guarantee the selectivity of interstage protection, so 4.1.2 specifies for non-critical loads. The protection device can be cut without selectivity. 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 selectivity of important loads. This technology has been introduced in China, in 4.1. Whether it is necessary to keep up with the progress of technology in Article 2 is reflected.
(7) The TN-C part of the TN-C system and the TN-CS system cannot be equipped with RCD, and only the zero-sequence protection with low sensitivity is used for ground fault protection. The writing of paragraphs 4.4.10 is intended here, but the terminology of the three-phase four-wire system is incorrect and should be changed to the TN-C system and the TN-C part of the TN-CS system.
(8) The leakage current action protector in 4.4.11 should be changed to the 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 IΔn in fire protection RCD in 4.4.21 shall not exceed 0.5A and should not be changed to more than 0.5A. 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 IΔn is not limited by 0.5A. The IΔn values ​​in the IEC product standard and the IEC60364 standard examples are all 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 clearly defined and explained 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, but they may not be coordinated with other provisions in the wording of the text, and may be subject to the US Electrical Code (NEC) idioms. reason. For example, the phases that are not grounded in this article are actually the phases, because the phase line in China is not grounded; and if the neutral point is not grounded and the N-line does not lead out, the three-phase three-wire power distribution system does not lead to neutrality. The line's IT system, the article read is puzzling. It should be expressed succinctly in accordance with IEC terms for ease of 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 in the provisions that this requirement only applies to TT and TN-S systems and should be deleted.
(12) In the building electrical installation, 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, as is the PEN line in the TN-CS system, while the PEN line does not appear in other grounded systems. Therefore, in 4.5.6, it is not appropriate to specify this requirement as only applicable to the TN-C system, and should be deleted.
4 Building electrical design specifications should be equivalent or equivalent to adopt IEC standards, and it is not appropriate to close the IEC standard, including the electrical design specifications including GB50054-95, to protect 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 responsibility for standardizing the preparation of the staff is small and the responsibility is 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. There are also many problems in building electrical design codes. But compared to the past, there is now a good condition, 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 IEC standard should be used equivalently or equivalently instead of the IEC standard. Some of the current norms are plausible and contradictory. In fact, the wrong provisions of the IEC standard can also be vaguely called the close IEC standard, because the word close is not defined, and the scalability is very difficult to scale.
China's building electrical design codes lack authority in the international arena, and even have not 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. I believe that the days when China's building electrical design codes are universally adopted by countries and become internationally authoritative norms will come soon. Source: Reposted from: cnbew
Factory Twisted Pair Cable,Twisted Cable,Telephone Cable
BLG Digital Network Co., Ltd. , http://www.gdnetworkcable.com