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发表于 2011-11-12 10:31
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没错，接地电阻测试时大家都默认可以不包括电源线的，那是认为三根线（L、N、G）阻值一样大，在这种失效模式下阻值过大其实没有关系。测试仪器其实是带校正功能的，直接短路两根绿色的线归零就去掉了测试设备的阻值，大家无需担心测试方法的问题。 5 u+ F5 h% B0 r& a
7 B6 j, L# u, }2 n6 y. L; ?但是这根电源线很蹊跷，用电桥法测试三根电线确实也是毫欧级，但是带载25A测试达到0.178欧，而L和N线带载25A却达不到这个阻值，你认为这根线的问题在哪里？ + Y8 u! t9 ]! G- t
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标准也是有明确从插脚算起来的：
9 h* ^8 x, l9 ]) I: O65.1 The resistance of the grounding path between any metal part that is required to be grounded (see
! G/ P4 ~1 w( R+ ^# G35.1.1) and the equipment grounding terminal or lead, or the point of attachment of the wiring system, or
! H8 v2 j8 [* m( D7 o| the grounding blade of an attachment plug |
, shall be no more than 0.1 ohm.
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当然标准也在变，不一定从插头算起（UL1573）： : a% q2 p) M6 a/ i. B* ^- @$ K: B
36.4 When an indicating device of the type described in 36.3 does not indicate continuity of the grounding circuit, an alternating current or a direct current of at least 25 amperes from a power supply of not more than 12 volts is to be passed | from the point of connection of the equipment grounding means to a point |
| in the grounding circuit and the points |
. The resistance in ohms is then calculated by dividing the drop in
, M9 E U7 [( S6 aUL153：
* [1 w! m6 d- X3 i. [/ d4 R* }136.2 Test method 0 n; _. y/ c x5 L$ x
136.2.1 The impedance between the point of connection of the equipment-grounding means and any other accessible metal part required to be grounded, shall be determined by applying a current of 25 amperes – derived from a 60 hertz source with a no-load voltage not exceeding 6 volts – | between the grounding connection and the metal part in question |
. The resulting impedance is calculated by dividing the value of the measured voltage by the applied current (25 A).
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7 r( y7 A* C& ` b7 N* ], }. u大家考虑一下，为什么厂家要把地线做成与L和N电阻不一样？
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