回复 6# 治学以诚
这几百栋楼都出什么问题啦？
本帖最后由 治学以诚 于 2010-7-7 10:38 编辑
楼上不许这样诘难俺(玩笑呵）。隐患，肯定有必然出问题的时候。
What the "electrical power supply institute" said is correct.
Everyone knows that electrons follow the path of lest resistance.
The smaller conductor has more resistance/distance than a larger conductor. It should see less current than the larger conductors but more heat too.
This is only part of the story!
"The charge is located more at the point".Electrons naturally travel toward the surface of a conductor and they will also congregate around the smaller radius of an irregular cross section.The conductor as a whole must be able to dissipate the heat!
(I believe that using two conductors of different diameters creates and irregular cross section without being able to share the heat.) The two large conductors lead in heating up as they do more current is shifted to the smaller conductor increasing it's temp until the point of failure. The "balance" is only good as long as the current doesn't cause the smallest conductor to exceed it's rating (3 times that of the smaller conductor.)
The smaller radius just compress the charge, whether it is moving or static. This wouldn't play apart in our situation. (This only come in to play someone is trying to make or avoid making a spark. As in determining what the insulation requirement for cable at different voltages.)
电力工程电缆设计规范
3. 7. 11 交流供电回路由多根电缆并联组成时，各电缆宜等长，并应采用相同材质、相同截面的导体；具有金属套的电缆，金属材质和构造截面也应相同。
为什么这样规定呢？
这是指为同一负荷供电的要求吧？和一楼问题有关吗？
以诚兄能不能系统地一次性把问题说说，别吊胃口嘛
老诚就好这口。。。。
老诚，这帖还没完呢。。。。。。
抽点空把这个帖给结了。本图为当前全国通用做法示意，这种错误做法应当立即纠正。
显然。当WP1中不平衡电流为I1=190A时，I2=70A，I3=120A。此时两根电缆运行情况相当于一根单芯导体流过70A电流，当套管选用钢管时，实际工程中选用的就是钢管。70A电流产生的涡流效应，会不会使管材温度升高，加速绝缘老化甚至脱落，笔者不敢妄言，但是可以肯定的是，这种情况违反了《电力工程电缆设计规范》5. 4. 1 .2 交流单芯电缆以单根穿管时，不得采用未分隔磁路的钢管。
当A点折断时，照明设备仍会照常运行，WP1中不平衡电流I1=190A，完全经WPE1电缆流回电源。两个电缆套管中除相当于单芯电缆穿钢管工况外，严重威胁WPE1电缆的安全。
总之，本人殷切呼吁，住建部能在全国范围内排查多电缆配电的安全性问题，对于所有多电缆去同一场所有N或PEN线共结点的工程予以整改。
PEN断了，问题就大了。
即使是多根一样的电缆并联，同样会出现其中某些电缆PEN断了的问题，也是很难发现的。
同时，本人对第一楼的图纸错误，深感悲哀，地市级甲级大院，就这样的水平，也吁请住建部能切实抓一抓设计单位的资质问题。
补充诚版主一小点哈，
检修WP1时，也必须断开WPE1，
否则PEN线有电流经过，会产生压降。
如果消防是一级负荷，则又违反了
“当一个电源发生故障时，另一个电源不应同时受到损坏。”
