JPR3, I am not a aware of a requirement for isolation in central offices from 295, and 1089 section 9 discusses connections of equipment installed in an IBN that now has multiple incidental or intentional connections to the CBN.
9.10 "This section contains criteria for tests to be performed on equipment that has traditionally been installed in an IBN but that is now intended for installation with multiple incidental or intentional connections to the CBN." To me these imply isolation is not required, but rather if necessary, these are the requirements to implement it correctly. My understanding is that Verizon (and perhaps others) have been moving away from IBN type equipment for some time, as it is difficult and costly to manage from a facilities standpoint (this would be a good thing for Chuck Graff to comment on). Another aspect from an historical perspective is that many of the components (disk drives, crts, tape storage units, PCs, etc.) which are commonly used throughout COs, were developed in accordance with ITE grounding and bonding schemes (connecting circuit references to frame ground). Depending on the circuits (analog vs digital), and the influences of concern (large potential differences in voltage, low level noise, EFT, surge, etc.), there are advantages and disadvantages to both both approaches. An appropriate approach requires an understanding of all the interfaces, the various influences to protect against, and the manner in which connections to other equipment will be made. My experience has been similar to Joe's, there is still a great deal of confusion as to when and where it is required. Regards, Mark F. Gill Sr. Engineer Solectron Technical Center 4222 Emperor Blvd, Suite 300 RTP, NC 27703 919-474-3569 markg...@solectron.com <mailto:markg...@solectron.com> -----Original Message----- From: j...@aol.com [mailto:j...@aol.com] Sent: Tuesday, September 10, 2002 2:58 PM To: emc-p...@majordomo.ieee.org Cc: jfinlay...@telica.com; dorin.op...@alcatel.com; john.juh...@ge-interlogix.com Subject: Isolated grounds in central office In a message dated 9/10/2002John Juhasz writes: Be careful Dorin. For Central Offices, they need to be isolated. Hi Guys: I changed the subject heading on this response (was "Inrush and EN61000-3-3") to better reflect the direction this thread has taken. The subject of isolating circuit ground from frame ground in a CO seems to be controversial. On one hand, I have heard stories such as John's about various RBOCs insisting on this. On the other hand, I have not seen the actual written requirements that were being imposed or the rationale behind them. For safety, functionality, and EMC considerations, I think it is generally better to tie circuit ground to frame ground in a robust fashion. One person told me that Verizon had insisted that circuit ground be brought out to an isolated terminal post that could then be externally tied to frame ground. This made a mess out of his design, and so far I have avoided this approach in my own designs without getting nailed. It seems that there is some confusion about whether this isolation is required and if so, why it is required. The whole subject of grounding within a CO can become quite complicated, especially when lightning is taken into consideration. I understand that TR-NWT-000295, "Isolated Ground Planes: Definition and Application to Telephone Central Offices" addresses some of these issues, but not in a clear manner (imagine that for a Telcordia document!). If anyone can provide a clear explanation of when isolation of circuit ground and frame ground is required in a C.O. and why, I would be most interested to know. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
