Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!ginosko!usc!trwind!johng
From: johng@trwind.UUCP (John Greene)
Newsgroups: comp.dcom.lans
Subject: Re: Repeaters Grounding Thin Ethernet coax lines.
Message-ID: <585@trwind.UUCP>
Date: 9 Oct 89 16:55:57 GMT
References: <3824.25292578@zeus.unl.edu> <2128@avsd.UUCP> <27682@amdcad.AMD.COM> <6638@pdn.paradyne.com>
Reply-To: johng@trwind.UUCP (John Greene)
Organization: TRW Information Networks Div
Lines: 31

In article <6638@pdn.paradyne.com> dixon@gumby.paradyne.com (0000-Tom Dixon) writes:
>In article <27682@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes:
>>You know, that actually brings up a good question. Repeaters SHOULDN'T
>>ground the cable on either side, but *a* ground for each thin Ethernet
>>must come from *somewhere*, and I doubt that most network installers
>>think to provide one. [It may be the case that these multi-thinwire
>>repeaters ground the "down leg" thinwires to their own chassis ground,
>>which would be the right thing to do in most cases assuming the chassis
>>ground is connected to the third or "green" wire, but they should never
>>ground the "up leg", i.e., the trunk or backbone connection.]
>
>But what about backbone thinnet segments?  This means that a thinnet
>segment that runs from repeater to repeater would be a gound loop.  
>This is not good.
>
>The Cabletron 8 port repeaters we use have 8 thinnet ports and 1 AUI
>port.  I would assume that we should hook backbone thinnet to a 
>non grounding transciever and hook that to the AUI port on the 
>repeater.  We presently are using the thinnet ports as you expect. 

All of the Thin-Ethernet transceivers that I have seen (read "taken apart")
have the shield AC coupled to the chassis ground.  The "ground" being talked
about recently has to do with providing a DC ground at a single point.  
Whether or not this is good practice I cannot tell you.  It seems that if you
provide a DC path to ground you are only asking to have your cable fried in
the case of lightning.    
-- 
John E. Greene    "People are just like frankfurters....You have to decide
                   if you're going to be a hot dog or just another wiener" DLR
TRW Information Networks Division 23800 Hawthorne Blvd, Torrance CA 90505
ARPA: johng@trwind.ind.TRW.COM  USENET: ..trwrb!trwind!johng