Hi Rich, Well, you know me, I'm not so easy to convince! Safety standards (well, at least IEC 60950-1) have various constructional requirements to ensure that not only is the connection good when it leaves the factory gate, but it has a good chance of staying that way throughout the life of the product. I do not recall any such requirement in CISPR 22 or the like. Take earthing as an example, since it is important for both safety and EMC... IEC 60950-1 has a requirement that when you screw through an insulating material which could shrink in use (such as a pcb substrate) then you need to use a resilient washer to maintain contact pressure if the contact is relied on for protective earthing. Perhaps this is more particular to safety because the fault currents can be very high, but if one or more EMC contacts are not made then the emissions are likely to increase and the immunity decrease. IEC 60950-1 has requirements to limit the electropotential when using dissimilar metals. This reduces the likelihood of corrosion occurring during the life of the product. IEC 60950-1 has various requirements regarding the type of screw and associated construction (e.g. number of engaged turns) that can be used for providing a protective earth connection. This ensures the resulting mechanical joint has a certain degree of robustness. Of course these constructions are in the standard because they have been found to work over the years. You could presumably replace the resilient washer requirement with some sort of thermal cycling and ageing test; perhaps the electropotential requirement could be replaced by a salt spray test; and the other constructional requirements replaced by a combination of thermal-humidity cycling and vibration test. In this way you would have replaced requirements that are easy and cheap to incorporate and inspect to by expensive and lengthy tests. But if you do not incorporate the performance tests then you have just diminished safety in the longer term, even if the unit happens to pass the earth bond test during type examination. Regards, Richard Hughes
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