Doug: Just to enhance your observation, at RF ( i.e. broadcast frequencies 520-1800 Khz) there is a pseudo resonant effect that places RF ground at different places in a building , home etc. The RF ground is dependant on the intereception of direct radiation and is related to how much wiring is exposed and the angle of exposure. It would make an interesting problem to model.
In one case, a CD system on a second floor was completely disabled by RF common mode) and the only way to re establish a ground reference was tying the ground lead from the CD player to the bedprings. It may sound far fetched, but it worked. Sometimes plugging into a different AC outlet in the same room , cleared the problem. Ground potential difference can also occur when transformer insulation becomes "leaky" , mainly due to age. Cheers. Ralph Cameron EMC Consultant for Suppression of Consuemr Electronic Equipment (After Sale) ----- Original Message ----- From: "Doug" <[email protected]> To: <[email protected]> Sent: Saturday, May 06, 2000 1:18 PM Subject: Re: Ground potential differences.... > > I'm going to stick my neck out here and say from two > experiences with this topic, there's a couple of things > to consider ... > > First, ideally, any potential difference between GROUNDS > should be zero. If you had asked about NEUTRALS, I'd have > to say - unknown. The physical connection is a function > of the connection to the transformer by the electricians > and imperfections in the transformer. > > Second, it's a function of what's sourcing the difference. > I worked at a place where the outlets in one half of the > lab were supplied by a different substation than the outlets > at the other end of the lab. > > Without knowing the issue, we connected two different machines > with a coax. Each machine eventually connected to different > substations by way of differently sourced outlets. And we > watched with amazement as the rubber jacket of the coax melted. > All with a 15V difference. The electricians were notified > and the problem was solved but a potential difference of > some sort was still there. I don't think you'll ever get > away from it. > > So, I guess what I'm saying is that you should not only > consider the voltage difference, but the power involved. > And that would be have to tested some other way. > > - Doug McKean > > Kelly Tsudama wrote: > > > > Hi gang! > > > > I have been asked to look into ground potential differences by one of the teams that I support. Can any of you provide any insight on how I can determine the maximum potential difference between different ground circuits within a building??? I've heard numbers ranging from 2V to 50V!!! Even with all the bonding requirements in the NEC, there must be some voltage differential between grounding points??? > > > > Thanks for any help you can provide. > > > > Kelly > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
