问题 单项选择题

关于综合布线隐蔽工程的实施,以下说法不正确的是______。

A.线槽的所有非导电部分的铁件均应相互连接和跨接,使之成为一个连接的导体
B.线槽内布放的缆线应平直,要有冗余
C.在建筑物中预埋线槽可为不同尺寸,按一层或两层设置,应至少预埋2根以上
D.线槽宜采用绝缘塑料管引入分线盒内

答案

参考答案:D

解析:线槽安装要求
(1)线槽应平整,无扭曲变形,内壁无毛刺,各种附件齐全。
(2)线槽接口应平整,接缝处紧密平直,槽盖装上后应平整、无翘脚,出线口的位置准确。
(3)线槽的所有非导电部分的铁件均应相互连接和跨接,使之成为一个连续导体,并做好整体接地。
(4)线槽安装应符合《高层民用建筑设计防火规范》(GB50045—95)的有关部门规定。
(5)在建筑物中预埋线槽可为不同尺寸,按一层或两层设置,应至少预埋两根以上,线槽截面高度不宜超过25mm。
(6)线槽直埋长度超过6m或在线槽路由交叉、转变时宜设置拉线盒,以便于布放缆线和维修。
(7)拉线盒盖应能开启,并与地面齐平,盒盖处应采取防水措施。
(8)线槽宜采用金属管引入分线盒内。
线槽内配线要求
(1)线槽配线前应消除槽内的污物和积水。
(2)在同一线槽内包括绝缘在内的导线截面积总和应该不超过内部截面积的40%。
(3)缆线的布放应平直,不得产生扭绞、打圈等现象,不应受到外力的挤压和损伤。
(4)缆在布放前两端应有标签,以表明起始和终端位置,标签书写应清晰,端正和正确。
(5)电源线、信号电缆、对绞电缆、光缆及建筑物内其他弱电系统的缆线应分离布放。各缆线间的最小净距应符合设计要求。
(6)缆线布放时应有冗余。
(7)缆线布放,在牵引过程中,吊挂缆线的支点相隔间距不应大于1.5m。
(8)布放缆线的牵引力,应小于缆线允许张力的80%,对光缆瞬间最大牵引力不应超过光缆允许的张力。在以牵引方式敷设光缆时,主要牵引力应加在光缆的加强芯上。
(9)电缆桥架内缆线垂直敷设时,在缆线的上端和每间隔1.5m处,应固定在桥架的去架上:水平敷设时,直接部分间隔距施3~5m处设固定点。在缆线距离首端、尾端、转弯中心点处300~500mm处设置固定点。
(10)槽内缆线应顺应顺直,尽量不交叉,缆线不应溢出线槽,在缆线进出线槽部位、转弯处应绑扎固定。重直线槽布放缆线应每间隔1.5m处固定在缆线支架上:在水平、垂直桥架和垂直线槽中敷设缆线时,应对缆线进行绑扎。4对对绞电缆以24根为束,25对或以上主干对绞电缆、光缆及其他通信电缆应根据缆线的类型、缆径、缆线芯数为束绑扎。绑扎间距不宜大于1.5m,绑扣间距应均匀、松紧适度。

单项选择题

When Dr. John W.Gofman, professor of medical physics at the University of California and a leading nuclear critic, speaks of "ecocide" in his adversary view of nuclear technology, he means the following: A large nuclear plant like that in Kalkar, the Netherlands, would produce about 200 pounds of plutonium each year. One pound, released into the atmosphere, could cause 9 billion cases of lung cancer. This waste product must be stored for 500,000 years before it is of no further danger to man. In the anticipated reactor economy, it is estimated that there will be 10,000 tons of this material in Western Europe, of which one table-spoonful of plutonium-239 represents the official maximum permissible body burden for 200,000 people. Rather than being biodegradable, plutonium destroys biological properties.

In 1972 the U.S. Occupational Safety and Health Administration ruled that the asbestos level in the work place should be lowered to 2 fibers per cubic centimeter of air, but the effective date of the ruling has been delayed until now. The International Federation of Chemical and General Workers’ Unions report that the 2-fiber standard was based primarily on one study of 290 men at a British asbestos factory. But when the workers at the British factory had been reexamined by another physician, 40--70 percent had X-ray evidence of lung abnormalities. According to present medical information at the factory in question, out of a total of 29 deaths thus far, seven were caused by lung cancer. An average European or American worker comes into contact with six million fibers a day. "We are now, in fact, finding cancer deaths within the family of the asbestos worker," states Dr. Irving Selikoff, of the Mount Sinai Medical School in New York.

It is now also clear that vinyl chloride, a gas from which the most widely used plastics are made, causes a fatal cancer of the blood-vessel cells of the liver. However, the history of the research on vinyl chloride is, in some ways, more disturbing than the "Watergate cover-up." "There has been evidence of potentially serious disease among polyvinyl chloride workers for 25 years that has been incompletely appreciated and inadequately approached by medical scientists and by regulatory authorities," summed up Dr. Selikoff in the New Scientist. At least 17 workers have been killed by vinyl chloride because research over the past 25 years was not followed up. And for over 10 years, workers have been exposed to concentrations of vinyl chloride 10 times the "safe limit" imposed by Dow Chemical Company. (422 words)

Notes: plutonium 钚。asbestos 石棉。polyvinyl chloride 聚氯乙烯。

According to paragraph 3, some workers have been killed by harmful pollutants in that()

A. production could not be halted

B. they failed to take safety measures

C. research was not pursued to a solution

D. safety equipment was not adequately provided

单项选择题