Folks, At my last company we nearly always performed EMC testing first on the basis that safety testing involves the insertion of purposeful faults that can damage the equipment whereas, with the exception of surge testing, EMC testing is relatively benign. EMC changes seldom affect safety? I guess that depends on the types of product you're talking about. On high-ish speed comms ports the EMC folks always wanted to tie everything to ground and yet from a safety perspective there was a concern that differences in earth potential between equipments could drive high currents down data cables and so an isolated approach was preferred. OK, this is something that should be sorted out in the design phase, but when it comes to meeting deadlines a quick EMC fix can compromise safety, and vice versa. Another example is when MOVs are added from supply to ground to get mains powered equipment to pass surge tests. I therefore do not think there is a universal answer of whether safety or EMC should be done first. Based on the knowledge of the equipment, which constituent parts have undergone prior testing, etc. it may be best to start with safety tests or EMC tests. Whatever the choice, the safety and EMC engineers need to know the changes introduced by the other party so they may make a determination of whether those changes are likely to adversely affect their discipline. Regards, Richard Hughes In a message dated 03/29/2004 19:52:51 GMT Standard Time, j...@jmwa.demon.co.uk writes:
>Certainly we would all prefer that our company's products be designed for >initial/immediate compliance, that we have multiple samples available for >testing, and that all the testing is completed without failure. However, in >the real world scenario of one sample for both safety & EMC, that may not >pass all tests, would you recommend that safety certification/testing be >done before or after EMC testing? The key issue being whether a "fix" for >one discipline will require a re-test for the other discipline. > >Personally, I have always recommended that safety be done 1st for two >reasons: >1) Changes for safety almost always affect EMC testing but EMC changes >seldom affect safety testing and, >2) Safety re-tests are far less expensive than EMC re-tests. > >Do you agree? Yes. In addition, you can draw a lot of correct conclusions about safety just by visual inspection, but EMC problems are almost entirely invisible unless very blatant.
