致歉公告

北方郎

回复 484# 治学以诚
貌似电击防护归根结底就是欧姆定律，电阻串并联。接触电压、电流计算

尺短寸长

回复 496# 北方郎

老诚嗤之以鼻：初中生读一遍都过分。{:sweat:}

rainmen_73

TT制的安全性必须基于RCD的可靠动作。RCD故障时的人身安全如何考虑，我的想法还是每个路灯设两圈等电位扁钢来解决问题。

尺短寸长

假如再考虑RCD故障时的人身安全，每个路灯设等电位联结就成为必然……
沿此思路深入下去，则大可不必采用TT系统，TN-S系统更有优势。

尺短寸长

问题在于：
目前的市政道路、工厂道路、住宅小区道路旁的路灯，无论采用TN-S系统还是TT系统，有做等电位联结的吗？

请教老诚：
老诚做道路照明是咋做的？

尺短寸长

434.5.2 For cables and insulated conductors, all current caused by a short-circuit occurring
at any point of the circuit shall be interrupted in a time not exceeding that which brings the
insulation of the conductors to the permitted limit temperature.
For operating times of protective devices <0,1s where asymmetry of the current is of
importance and for current-limiting devices k2S2 shall be greater than the value of the letthrough
energy (I2t) quoted by the manufacturer of the protective device.

For short-circuits of duration up to 5s, the time t, in which a given short-circuit current will
raise the insulation of the conductors from the highest permissible temperature in normal duty
to the limit temperature can, as an approximation, be calculated from the formula:
t = (k * S / I)2   (3)
where
t is the duration, in s;
S is the cross-sectional area, in mm2;
I is the effective short-circuit current, in A, expressed as an r.m.s. value;
k is a factor taking account of the resistivity, temperature coefficient and heat capacity of
the conductor material, and the appropriate initial and final temperatures. For common
conductor insulation, the values of k for line conductors are shown in Table 43A.

老诚会说：你什么都不懂！

rainmen_73

回复 500# 尺短寸长

目前实际状况如不做市政设计的都不见得清楚，这个论坛上应该有。我想，可以从施工投资维护的角度来说说单灯做等电位联结的可行性。如此做法能推广，善莫大焉

北方郎

回复 497# 尺短寸长
看来能入老诚法眼的文章十分罕见