Date: Fri, 04 Aug 2000 16:04:31 -0400 From: "Louis A. Mamakos" <louie@TransSys.COM> To: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> Cc: freebsd-questions@FreeBSD.ORG (questions FBSD) Subject: Re: Router "ep2" issue Message-ID: <200008042004.QAA85387@whizzo.transsys.com> In-Reply-To: Your message of "Fri, 04 Aug 2000 11:40:18 PDT." <200008041840.LAA80077@gndrsh.dnsmgr.net> References: <200008041840.LAA80077@gndrsh.dnsmgr.net>
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[Note trimmed To: and Cc: to freebsd-questions]
>
> > The spec does call for medium grounding for 10Base5 and allows for it
> > (but does not require it) for 10Base2, but that's about it.
>
> Anyone running Coax of any real length is a fool not to have it
> properly gounded. Without the ground it is one big antenna, and
> in a lightning storm the EMP wave can induce 100's to 1000's of
> volts on a long piece of ungrounded coax, especially something
> as large as 10Base5.
I observed this first-hand years ago when 10Base-5 ("Thick" ethernet
to you, buddy!) was run between two building, and underground at
that. A lightning strike nearby caused the premature death of a
bunch of thick ethernet transceivers, most convieniently located
in the ceiling above various offices.
There was also a considerable DC offset in the ground between the
buildings, on the order of a couple of volts! I don't know if anyone
ever measured the current when the cable was connected to the bulding
ground in each building. I think this is why you're only supposed
to ground the ethernet shield conductor in exactly one place.
louie
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