Hi Chris Well the pressure is from competing EMC gurus who think that the ground rods "feel" like the right thing to do. They have not been able to lend much logic to the discussion. On the other hand I have a lot of NEC types that have been raising red flags like myself and we have been raising red flags about safety. No I would not say there is anything realy unique about the 3 phase power topic other than the installation class is often III. I am presently designing a Power Quality Meter and need the power supply and metering circuits to take quite a 6KV surge.......and the EFT is 4KV. I also push the RF radiated immunity beyond 20V/M with modulation. So far that has not been a problem.
Chris From: "Chris Maxwell" <[email protected]> To: "Robert A. Macy" <[email protected]>; "Chris Wells" <[email protected]> Cc: <[email protected]> Sent: Wednesday, April 06, 2005 4:06 PM Subject: RE: EMI ground plane reference versus NEC single point earth bonding Chris I read this thread; and I'm reluctant to answer because I'm not sure where the "pressure" to install ground rods is coming from. So, if you read my thread below, you'll see that I'm not giving you an answer...I'm really asking you a question. The Ground Reference Plane (GRP) is all you need for EFT, Surge and other transient testing according to the IEC 1000-4-X series of standards. According to the standards, you are only required to have the GRP extend beyond the EUT a certain distance; and you are required to tie the GRP to your building's Earth ground. The equipment designed for using such test setups (surge generators, transient generators ...) are designed with this GRP in mind. They have bond straps that reference this plane in order to make your testing repeatable. I haven't seen a manual for one that ever demanded a ground rod to be driven. End of story. Most of what I've said above is well known among people in the EMC community; so I'm wondering why anybody would "pressure" you to deviate. This is where my reluctance arises. Is there something special about your test setup? Are you testing equipment that just wasn't taken into account when the IEC 1000-4-x standards were devised? Is there some issue because you test 3 phase equipment? Is your building on a huge deposit of volcanic pumice with almost no conductivity whatsoever? Does your building have old wiring with insufficient ground conductors back to the power entry panel? Who is pressuring you and for what reason? This is one of those questions where I would love to say "there's no way that you should have to drive a ground rod" because I can't think of a reason why...Problem is...I'm wondering if you have a valid reason... So...Why would you want to drive ground rods??? Throw that piece of information out there; and I think you'll get your answer. Chris Maxwell Design Engineer Nettest 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
