On Sat, 13 Oct 2012 16:35:08 -0700 (PDT), klem kedidelhopper
wrote:

A friend is doing his own network wiring.

Find a new friend that doesn't do their own network wiring.
I'll resist the temptation to crosspost this to comp.dcom.wiring.

he ran an underground shielded cable between metal junction
boxes mounted on the outside of two buildings.

How far and what type of cable? If it's shielded CAT5E or CAT6 (ScTP,
FTP, STP, S/UTP, etc)
http://en.wikipedia.org/wiki/Foiled_twisted_pair#Cable_shielding
then there's a chance it will work. If the cable is some kind of
microphone or signal cable, forget it.

The shield is grounded
at one end, not connected to anything just wrapped and taped at the
other, (this was my suggestion).

Ummm.... He's suppose to use shielded RJ45 connectors.
https://www.google.com/search?hl=en&q=shielded+rj45&tbm=isch

So far everything sounds OK.

Nope. No numbers for cable, length, or connectors.

He's apparently taken a twenty foot
network cable with RJ45's on either end, chopped it in half, and wire
nutted this to the underground color for color at each end.

Barf. That might work for slow 10BaseT/HDX (half duplex), but will
not fly for FDX (full duplex), 100Mbits/sec or Gigabit.

He plans
to connect this between the new computer which he hasn't received yet
and the network.

What's on the other end of the cable?

I told him that he should have used a termination
block and offered that worst case this arrangement won't work at all.
Best case he'll suffer a significant loss of speed. He doesn't believe
that there will be any problem with this at all though, and if it is
it would be minor. So who's right? Can this type of cob job work, and
if so would performance be significantly compromised, and how much?

If (and only if) the original cable is CAT5 or CAT6, then the easiest
fix is to put RJ45 plugs or jacks at the end points. If he needs to
add 10ft of CAT5 or CAT6 on each end, then do it with a proper patch
cable. Lose the shielded (un-necessary) and the wire nuts.

Type 66 punch down blocks sorta work at 10mbits/sec, but screw up
badly at 100mbits/sec (my experience). Type 110 punch down blocks do
better, especially when they are specifically designed for networking.
However, nothing is better than an RJ45 connector.

I don't care to speculate on exactly where it will screw up. I just
know it will fails somewhere.

Incidentally, if this is a ham operator, and the shielding is to
eliminate RFI, shielding is not going to help much. I know several
super stations that are using 2.4 and 5.7GHz Wi-Fi in place of
ethernet cable solely to eliminated RFI.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558