我的想法是：
1. 60664-1的6.2主要是针对爬电距离距离，对电气间隙没有影响
2. 表格下面有句话If the associated clearance is less than 3 mm, the minimum dimension X may be reduced to one-third of this clearance.
3. 如果电气间隙只有0.5mm，最小限值就是0.5mm除以3，肯定小于0.5mm，所以是可以测量
本人只看了clause 6.2，如有不妥还请指正。
就有60664，看到这个贴的人我想都会搜索，就不写链接了作者: 日夏清 时间: 2011-12-10 11:18
1. 章节应是4.2.
2. 如果电气间隙只有0.5mm<3mm，X取0.5mm/3，所以是可以测量.
3. cl 29.1 of IEC 60335-1有这么一段话：However, if the construction is such that the distances could be affected by wear, by distrotion, by movement of the parts or during assembly, the clearances for rated impulse voltages of 1500V and above are increased by 0,5mm and the impulse voltage test is not applicable.
因为实际上你的器具一般会在移动或装配过程中会受到磨损、变形等影响，表16中对应1500V一般应在0,5mm上加0,5mm，即取1mm.作者: oahemr 时间: 2011-12-10 11:19
还有一种情况我们不能忽视：在功能绝缘的情况下，电气间隙ok，但爬电距离不够我们可以用脉冲电压进行验证，所以此时就算是爬电距离不够的情况下，此时的电气间隙也是有意义的。