1.1 The source of the grounding requirements should be reliably grounded
The compilation and promulgation of "Architectural Lighting Design Standards" (GB50034-2004, hereinafter referred to as "Standards") has made important contributions to the development of lighting industry and lighting energy conservation in China, and should be highly evaluated. However, the author believes that the fly in the ointment is 7.2.12 "When Class I lamps are used, the exposed conductive parts of the lamps should be reliably grounded"
(hereinafter referred to as Class I luminaires should be reliably grounded). Since the previous industrial enterprises and civil building lighting design standards have not had similar regulations, and the designers have long been immersed in other relevant norms and technical measures, they have the impression of “no grounding†and “no groundingâ€. The new provisions made should be referred to the interpretation of the provisions. I would like to elaborate on the safety of the person and the wide-ranging regulations. For example, the problems that existed before the provisions were made, the cases of electric shocks that occurred, the odds, etc., did not explain the results. Description. There is only such a simple phrase "in accordance with the classification standards of lamps and lanterns", and there is no explanation on what is meant by "class I lamps". The "numbering standards for lamps and lanterns" on which it is based is also not marked with its document number.
1.2 The classification standard of lamps stipulates that the grounding of lamps is suspected to cross
The author has found out from the classification of lighting products of "National Civil Engineering Design and Technical Measures Building Products Selection Technology (Electrical)" (2004CPXY), according to the degree of electric shock resistance of the lamps: Class I (original I level) lamps --- Grounded luminaires correspond to the interpretation of the standard 7.2.12.
The luminaires are different from the general floor-standing electrical equipment. They are generally located at a height that is beyond the reach of the human hand. When the luminaire is less than 2.4m from the ground, it must be grounded. This is stipulated in Article 19.1.6 of the National Compulsory Provisions for Engineering Construction Standards (Building Construction, 2002 Edition, hereinafter referred to as “Strong Barâ€). For lamps above 2.4m, according to the "Low-Voltage Power Distribution Design Specification" (GB50054-95, hereinafter referred to as "Low-Regulation") Article 4.4.2 and "Civil Building Electrical Design Specification" (JGJ/T 16-92, hereinafter referred to as Article 14.4.3 of the "People's Regulations" has five provisions that can be ungrounded. Articles 14.4.4 of the "People's Regulations" and the "National Civil Engineering Design Technical Measures Electrical" (hereinafter referred to as "Technical Measures") 9.1.16 also have four identical provisions that prohibit the protection of grounding. Therefore, whether the Class I luminaires are to be protected and grounded should be determined by the designer according to the relevant design specifications, depending on the level of use voltage, location or degree of insulation, etc., and should not be determined by the “classification of lampsâ€.
In view of the above, the regulation of the electric shock classification of the luminaire may be rewritten as a Class I luminaire--a luminaire with a clearly marked grounding terminal for grounding.
Implementation of 2I lamps should be reliably grounded
2.1 Current implementation overview
The requirements for reliable grounding of Class I luminaires in the Standards have been more than two years since the implementation date of December 1, 2004, and their implementation can be described as follows: a. Implemented. Among the implementers, there are also differences. In the distribution system diagrams and planes of the construction drawings, the added PE lines (3 lines) are marked; there are double executions, that is, thick steel pipes have been used. Wiring, plus PE wire. In 2005, after participating in the construction drawing seminar of a project designed by the field, after the author expressed his opinions on the grounding of all the lamps, the designer expressed the same feeling and hoped to reflect upward and make a joint appeal.
b. Not implemented. Someone asked in the past, even the ungrounded ones that have just been built can be looked at, then, is it necessary to increase the grounding? Some people think that there has been no problem with the PE line in the past; some have not yet figured out what happened to the Class I lamps; some have considered that there may be more dangerous electric shocks and so on.
c. Like an executor. On each floor plan and system diagram, note that “PE lines are added when all types of lamps are encounteredâ€, and the problem is pushed out.
This is a way of expressing an unexecuted person.
As a national standard, the Standard has been implemented for more than two years. It should be abnormal. It should be resolved as soon as possible.
2.2 Problems to be paid attention to in the implementation of reliable grounding of Class I lamps
a. According to the general provisions of the Standard, the Standard applies to new construction, reconstruction and expansion projects. For the reconstruction and expansion project, it is first necessary to clarify the original system grounding type so that the grounding type used matches the original system. Connect the PEN to the TN-C system (the old word is connected to zero); for the TN-C-S system, when the N line and the PE line in the PEN line are completely separated from the PEN, the PE is separated from the PE; for the TN-S The TT system is connected to the PE line protection, and the reliable grounding is the general name mentioned above. Since the introduction and adoption of the TN-S system, the PEN is no longer connected to the TN system building, but the PE line is connected.
b. As a lighting protection against electric shock, it is one of the ground fault protection. Generally, the leakage protector is not used to cut off the power, but the overcurrent protection device is also used as the ground fault protection to cut off the faulty power supply.
However, due to the protection of electrical products and construction quality, maintenance management level and changes in use, the cutting action is not completely reliable, so the IEC standard and other total equipotential bonding are listed as the basic conditions for ground fault protection.
4.4.4 of the fourth section of the "Low Regulation" grounding fault protection shall stipulate that the building shall be the total equipotential bonding; 4.4.5 shall stipulate that when the protective electrical appliance cannot cut off the faulty power supply within the specified time, it shall be in the local range. Internally assisted equipotential bonding. Special attention should be paid to the reform and expansion projects.
3 doubts about the reliable grounding of Class I lamps
Things are always divided into two. The reliable grounding of Class I lamps has its positive effects, and the author still has two negative concerns.
3.1 may lead to dangerous electric shock
In real life, because of its "narrow" and "high pressure", high-voltage electricity is generally not dare to touch, and it is repaired by professionals. It has few direct contact with electricity; low-voltage electricity (220/380V) is low-voltage and wide-faced. Sometimes, people who are ignorant and do not understand electricity are playing with them, so they are much more affected by electric shocks than high-voltage electricity, especially in lighting systems.
The protection against electric shock of Class I lamps is one of the protections in “ground fault protectionâ€. It is only a kind of protection for people who accidentally touch the metal casing of electrical equipment that is not charged under normal conditions and is charged due to insulation damage. Indirect protection, but no direct contact with direct contact and live conductors.
When the lighting is overhauled, there is no time for maintenance. At this time, it is often the case that the lampshade is held in one hand or the metal casing is supported, and the lamp is replaced or repaired. Once one hand accidentally touches the charged body and the other hand holds or touches the grounded metal casing, the electric current is transmitted from one hand to the other through one hand. This is the most dangerous and serious, and often causes electric shock and casualties.
3.2 will cause a lot of money, copper is idle for a long time idle
In the past, it was often said that "copper is a national strategic substance." In the past, such as the theater, only the part of the stage uses copper wire, and the audience hall uses aluminum wire. Today, copper wire is basically used in buildings. Today, the country is still not rich, and capital and copper are not too much oil. It is also necessary to cherish people's questions: Class I lamps with a height of more than 2.4m, which most people can't touch. In the past, there was no general requirement for “reliable groundingâ€. What happened in the end? What is the chance? It is worthwhile to spend a lot of money and materials idle for a long time to fully understand people-oriented. In lightning protection design, all buildings are not required to have reliable lightning protection facilities, and there is “acceptable annual average maximum number of lightning strikesâ€! Automatic fire alarms are also not required. Is it really necessary for today's Class I luminaires to be grounded? Moreover, it is not absolutely safe, and there are still more serious negative problems mentioned above.
4 Focus on developing and strengthening publicity and education on safe electricity use
At present, the masses have limited knowledge of electricity and knowledge about safe electricity use, and the knowledge of grounding protection is more limited. I remember the words "Must be grounded" on the instructions for imported washing machines. Someone asked how to ground? Answer: Someone tied the wire to the outer casing of the washing machine, and then placed the wire on the ground, which is "grounding." The other said: No, it is OK to connect the washing machine casing to the water pipe. Fortunately, someone immediately stopped saying: No, the original system is TN-C connected to the PEN line ("zero"), the water pipe is grounded (TT), the two systems can not be simply mixed. Once the washing machine phase line touches the casing leakage, and the porcelain insert insurance does not operate to cut off the power supply, the water pipe connected to it is dangerously charged. The most dangerous situation is that if someone holds the washing machine casing connected to the PEN line in one hand, the other hand will open the faucet on the leaking water pipe, and then through the electric shock circuit of the heart, Danger! I hope that there will be no people who have seen or heard the way that the lamps should be grounded reliably.
The above example shows the importance of developing and strengthening the use of electricity safety education, including the state under which to avoid overhaul or contact with electrified bodies, and the auxiliary safety measures that can be taken during maintenance, including light steel keels equipped with Class I lamps. Anti-shock measures during the decoration and maintenance of the ceiling.
5 overview
a. Whether the Class I luminaire is reliably grounded shall be determined by the designer according to the relevant design specifications, combined with the voltage of the electric power, the height of the installation position, the environmental conditions of the installation occasion, etc., and shall not be determined by the classification of the luminaire.
In the classification of lamps against electric shock, Class I lamps should be marked with lamps with obvious marking grounding terminals for grounding.
b. Class I luminaires are reliably grounded to have a certain role in preventing electric shock, but it is not absolute. It has the possibility of causing more dangerous electric shock. At the same time, there is still a lot of money and copper being left idle or permanently idle. Therefore, it is prudent to treat the luminaires set above 2.4m.
c. A comprehensive understanding of people-oriented, to investigate the probability of electric shock before the implementation of grounding, casualties, and weigh the input and output.
d. When implementing grounding, pay attention to the problem of total equipotential bonding and local auxiliary equipotential bonding, especially the modification and expansion project, and pay attention to the matching problem between the old and new grounding systems.
e. Protection against electric shocks should carry out and strengthen publicity and education on safe use of electricity and take auxiliary safety measures.
f. Highly evaluate the preparation and promulgation of the Standard. Only the provisions for the reliable grounding of Class I luminaires should be withdrawn from it and resolved by relevant design specifications.
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