In our prescreening lab we have a ~9M square metal floor plate that we tie direct to the Generator when doing IEC61000-4-4, -6 testing etc. The Generators and coupling devices are bonded high frequency wise to the plate and are also referenced to safety ground as per the NEC going back to the transformer earth grounding pad. In my view that is adequate for these high energy tests. the return path of the test signal is back to the plate, and all the gear is well within the permiter of the plate. However I am getting pressured to add localized ground rods next to the floor plate. I do not see how tying this plane to the earth has much EMC meaning unless we were doing emission uV type measurements. For that work we have a large GTEM which sits on the plate as well. I do see that a redundant local ground would violate NEC and that fault or surge currents would take the parallel path to my redundant ground rods causing risk to equipment and personel. We are on a hill and have been hit by lightening many times. We are also a power lab and are testing 3 phase equipment (480V P:P) As such I must be mindful of the safety topic perhaps more than others. If we were to instal an isolation transformer at the room that serviced all the gear and DUT, then we could establish a local ground that would satisfy both NEC and EMC type testing but the cost is an issue that would have to be rationalized and explained clearly to upper management. ( the transformer would have to be rather large and the building is leased) Right now I can not support the argument for either local ground rods or the isolation transformer. So please help me understand what the rational is for earth grounding locally the reference plane with ground rods. Is it like I thought, a uV issue with emission tests or does it actually have some bearing on high energy EFT, RF conducted type tests? If you can copy my work email that would be helpful. [email protected] IT won't let me get the list at work :-( Thanks in advance! Chris Wells Eaton Electrical ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/
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