Fact: The ground plane must be connected to the power source reference for safety. But the power source reference ground rod can be far away from the ground plane and you can be perfectly safe from an electrical fault. Only the integrity of the connection (ampacity and resistance between ground plane and power source neutral) is important.
Fact: At rf, the ground plane is the reference for all your rf and transient sources, it again requires no connection to another "ground" to work. My Conclusion: The only reason for local ground rods is lightning protection. > > > On Wed, 6 Apr 2005 07:53:56 -0400 > "Chris Wells" <[email protected]> wrote: >> 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 >> [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/ >> >> To post a message to the list, send your e-mail to >> [email protected] >> >> Instructions: >> > http://listserv.ieee.org/listserv/request/user-guide.html >> >> List rules: http://www.ieee-pses.org/listrules.html >> >> For help, send mail to the list administrators: >> >> Scott Douglas [email protected] >> Mike Cantwell [email protected] >> >> For policy questions, send mail to: >> >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >> All emc-pstc postings are archived and searchable on the >> web at: >> >> http://www.ieeecommunities.org/emc-pstc > > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/listserv/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
