Hi Geoffrey, You pose a good question with regard to EFT testing. We have been over this one in the past, and after consulting with several experts, we have come up with the following:
Although many commercial test labs recommend that you test all possible line coupling combinations (for a total of 7 if you are dealing with singe phase.), We have detirmined that Common mode testing is all that really needs to be accomplished. The thoughts behind this are that due to the rise times involved with the pulses, capacitive coupling within the power cable and power supply converts the differencial bursts to common mode anyway. We do however, test the lines indivdually as well, for the simple reason of satisfying the demands of our customers. What we end up testing is 4 combinations; L1, L2, GND, and Common mode(all three). I would be interested to hear other's thoughts on this subject....... Regards, Randy Flinders EMC Test Engineer Emulex Network Systems [email protected] * Opinions expressed are personal and in no way represent the position of Emulex Corporation. ---------- From: Geoffrey Skanes[SMTP:[email protected]] Sent: Thursday, July 31, 1997 12:53 PM To: emc-pstc Subject: Interpretation of IEC 1000-4-4 ---------------------------------------------------- Hi: I've recently had a need to re-visit the application of EFT pulses on AC power cords. Although the current version of the std. (1st ed.,1995) discusses assymetric application of the EFT pulse (Section 6.2), the std does not explicitly describe that the pulse application must be done on one conductor at a time. Considering Figures 4 and 11, it would appear that pulses can be applied to the protective earth (ground). Question is, is simultaneous application of the burst (in common mode) a valid and necessary test case? I believe the answer is yes for the following reasons: - I/O lines are exposed to EFT via the capacitive coupling clamp in true common mode, so why would power cords be treated differently? - for the same reasons that I/O cables are exposed to common mode burst events in reality, power cords should be exposed to common mode events. - A number of commercial stds, i.e. ETS 300-342-2, describe common mode application of the burst. Anyone else with comments on this? Regards, Geoff Skanes EMC Engineer Nortel Technology RTP, NC
