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
