[Beowulf]Infrastruture planning for small HPC 40/100 gigabyet eyhernet or Infiniband?
james.p.lux at jpl.nasa.gov
Mon Jul 28 10:19:10 EDT 2008
Quoting "Robert G. Brown" <rgb at phy.duke.edu>, on Mon 28 Jul 2008
06:15:44 AM PDT:
> On Mon, 28 Jul 2008, Eugen Leitl wrote:
>> On Sun, Jul 27, 2008 at 07:19:56PM -0700, Jim Lux wrote:
>>> bear in mind that ordinary ethernet both coax and twisted pair is
>>> galvanically isolated.
>> This is strange, because I've seen (small) sparks and received (mild)
>> shocks from both, in two different locations.
> Ground loop. Very dangerous. You go first...;-)
Very odd.. I'd be looking for an outright short from the cables to
something (or, a LOT of capacitive coupling)...
After all, the twisted pairs are isolated at BOTH ends..
Now, there is Power over Ethernet these days.. Basically uses each
pair of wires as a single conductor (i.e. they feed the juice in at
the center tap of the isolation transformer) but, again, that
shouldn't be sparking/shocking.
>> As you say, http://www.apcmedia.com/salestools/FLUU-5T3TLT_R1_EN.pdf
>> claims Ethernet is immune, yet I've read somewhere that Gigabit ethernet
>> is more susceptible than Fast Ethernet. I've got (cheap) UPSen for
>> almost all equipment, maybe they're the problem and not the switching
>> power supplies.
>> In any case I'll have an electrician diagnose the problem. Unfortunately,
>> I anticipate his solution would involve pulling through a new
>> ground wire to several locations. It is at this point that lack of wall
>> conduits will become quite painful.
Nope.. shouldn't require a separate grounding conductor, at least not
along with your cabling.
What you might want to do is see if your electrical safety ground
(third pin/green wire ground) at the two ends is at a radically
different voltage. You might have a miswired receptacle.
You should be able to just drag a single conductor through the house
and use a multimeter to measure the voltage between the ground pins,
and it should be zero, or pretty darn close.. use the AC setting, and
put a small (few K) load resistor across the meter, so you don't get
fooled by electrostatic/electromagnetic coupling... which will induce
several volts, at least into an open circuit.
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