You don't say, but I assume that the test set-up is CISPR 22 or ANSI C63.4 or some variant thereof. If it is in fact a test on equipment that mounts in a vehicle, then my answer would be quite different.
Tabletop mounted equipment mounts 80 cm above ground on a non-conductive standoff. Capacitance to ground is thus not precisely controlled, but clearly limited to a few tens of pF. If the test sample is wired with a three conductor power cord, the green wire should go to ground where the LISNs are attached to ground. In fact many commercial LISNs are supplied with a female power socket designed for the standard male power plug. The green wire conductor is taken to the LISN chassis. Floor mounted equipment is also isolated from ground, although it is necessarily closer to the ground plane. Safety ground is treated same as above. >From the point of view of conducted emissions, you will measure higher CE when the test sample case is directly bonded to the ground plane than when it is isolated. The mechanism for common mode conducted emissions is relying on either the green wire or the capacitance to ground to drive cm CE into ground. Differential mode emissions are unaffected by equipment case connections to ground, or the lack thereof. > From: "Boris Yost" <[email protected]> > Reply-To: "Boris Yost" <[email protected]> > Date: Mon, 14 Jul 2003 13:02:16 -0400 > To: "Emc-Pstc@Majordomo. Ieee. Org" <[email protected]> > Subject: Conducted emissions--green wire? > > > Dear Listers: > > I recently watched a conducted emissions test. Said test technician > connected Line to a LISN, Neutral to a LISN, and ground got stuck in a piece > of foam to keep it from touching anything. This bothered me and I > questioned this. However, according to said test technician, that is what > they are supposed to do. > The LISN's and the EUT were put on a metal table surface. The LISN's were > well strapped down, but my thing was just sitting there. Doesn't this mean > that the impedance of the EUT is some random number depending on the > materials and surface finishes of the table, EUT, and where they put the > LISN's? The stand I used for the EUT isn't really part of the EUT, just > something I had to hold it up. What happens when somebody else mounts a > display on a furniture lift and puts it in a piece of wooden furniture? > > Boris > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
