[net.lan] Do you ground your Ethernet cable?

evan@pedsgo.UUCP (Evan Marcus) (05/02/86)

There is a real debate raging around my office; we have an Ethernet cable
that supports 25 Interlan Ethernet Terminal Servers, and about a dozen
direct machine connections onto Ethernet.  The question is whether or not
we should ground the cable.  I have heard 'yes' 'no', and even a 'maybe'!
I am not an EE, so I do not know about these things.  

Do people ground their Ethernets????  

Send me E-mail, and (as usual) if there is more than a couple of responses,
I will summarize to the net.
-- 
NAME:   Evan L. Marcus
UUCP:   ...{pesnta|prcrs|princeton|topaz|hjuxa|vax135}!petsd!pedsgo!evan
USnail: CONCURRENT Computer Corporation (a Perkin-Elmer Company)
	M/S 308, 106 Apple St., Tinton Falls, NJ  07724
MA BELL:(201) 758-7357
QUOTE:  "OK, Mr. Richie, if you like.  'You.  Me.  It together.' "

jbn@glacier.UUCP (05/18/86)

       The Ethernet I spec called for the outer conductor of the Ethernet
cable to be ungrounded.  Because the connectors are uninsulated, this
created a safety hazard (a short to the braid due to wear between two
rubbing cables, one Ethernet and one power cable would
electrify all the exposed Ethernet connectors but wouldn't blow any breakers) 
and violates the U.S. National Electrical Code.  So the Ethernet II spec 
calls for grounding the Ethernet at exactly one point.
       Back at Ford Aerospace, we grounded our Ethernet with a copper
strap brazed to one of the connector barrels; the copper strap connected
to the building ground system (3/8" x 1.5" copper busbars under the
raised floor tied via heavy copper cable to the grounding rods out back
of the building and cross-connected to power system ground at the wye
of the main transformers; overkill, but a place that builds antennas
takes a dim view of RF noise.)

						John Nagle

portman@lll-lcc.UUcp (Roland F. Portman) (05/21/86)

In article <7584@glacier.ARPA> jbn@glacier.UUCP writes:
>
>       The Ethernet I spec called for the outer conductor of the Ethernet
>cable to be ungrounded.  Because the connectors are uninsulated, this
>created a safety hazard (a short to the braid due to wear between two
>rubbing cables, one Ethernet and one power cable would
>electrify all the exposed Ethernet connectors but wouldn't blow any breakers) 
>and violates the U.S. National Electrical Code.  So the Ethernet II spec 
>calls for grounding the Ethernet at exactly one point.
>       Back at Ford Aerospace, we grounded our Ethernet with a copper
>strap brazed to one of the connector barrels; the copper strap connected
>to the building ground system (3/8" x 1.5" copper busbars under the
>raised floor tied via heavy copper cable to the grounding rods out back
>of the building and cross-connected to power system ground at the wye
>of the main transformers; overkill, but a place that builds antennas
>takes a dim view of RF noise.)
>
>						John Nagle

One additional note, just be sure to ground only ONE end otherwise
nasty ground loop currents could creep up and cause major problems.

Roland

jbn@glacier.ARPA (John B. Nagle) (05/26/86)

      Yes, you ground your Ethernet at EXACTLY one point, or you get
terrible ground loop problem.  Ethernets are DC-coupled and hum-sensitive.

					John Nagle