In article , "J. Clarke"
wrote:

On 7/7/2010 8:30 AM, Joseph Gwinn wrote:
In ,
"DoN. wrote:

On 2010-07-07, Joseph wrote:
In ,
"J. wrote:

On 7/5/2010 9:47 PM, Joseph Gwinn wrote:
In ,
"DoN. wrote:

[ ... ]

The ohmmeter says it is good -- so it must be good. :-)

We did not try to explain it to him. It would be a magic show at best.

I have had the need to explain such things to other electricians, and
gotten a
big fight for my trouble. A person who does not know what he does not
know, or
even that there are such things.

That's one thing that bugs me about the State of Connecticut, one _must_
have an electrician's license to work on network cables. Never seen an
electrician with said license yet who could identify a cable scanner,
let alone who owned one,.

Yes. An iron rice bowl:http://en.wikipedia.org/wiki/Iron_rice_bowl.

Does this apply to:

1) Network cabling outdoors?

2) Network cabling in commercial or apartment buildings?

3) Or even home wiring?

Depends on the local laws, I suppose. One should not be expecting a real
technical rationale.

In Connecticut if you get paid to touch premise wiring you need the
license unless you work for the phone company, which has a specific
exemption. That includes network cabling outdoors, network cabling in
commercial or apartment buildings, and home wiring. Homeowners in most
areas can do their own wiring subject to permitting and inspection.

When our house was being expanded, I ran some thicknet ethernet
cable (picked up big spools of it at a hamfest) between several places
where networked computers are sometimes set up. Had I known about
100BaseT and faster coming down the pike, I would have put in Cat-5
cable instead.

Hmm ... also -- does it apply when running ethernet through
fiber optics? No wires there at all! No excuse for needing someone who
is accustomed to wiring voltages around. :-)

Hmm. This could be fun! Well, it looks like a wire....

The law is specific about the definition of "electrical work" and it
looks like fiber is exempted. So is wiring under 24v used for
controlling lawn sprinklers--if you have a network-aware law sprinkler
attached to your LAN does that mean that you're exempt?

Definite iron ricebowl issue.


And how about today's WiFi?

Clearly, does not apply.

The definition is: (2) "Electrical work" means the installation,
erection, maintenance, alteration or repair of any wire, cable, conduit,
busway, raceway, support, insulator, conductor, appliance, apparatus,
fixture or equipment that generates, transforms, transmits or uses
electrical energy for light, heat, power or other purposes, but does not
include low voltage wiring, not exceeding twenty-four volts, used within
a lawn sprinkler system;"

One could argue wifi either way.

Given that radio communications is a major use, and yet isn't mentioned, it
ought to be an easy argument.

And the backup argument would be that obviously the electricians need to obtain
radio transmitter licenses from the FCC before touching any such equipment.


Granted, I have a friend with an old house where it does not
work well at all. The walls are not drywall, but rather real plaster
over metal mesh. But I can't imagine an electrician knowing enough
about that to even diagnose the problem. :-)

Eight or nine years ago, I paid an electrician to install the CAT5e cable
from
basement to my wife's office on the second floor, and I will say that the
electrician and his helper earned their pay on that one. It's an old
house,
with wood lath plaster and strategically-placed bricks as fire-stops. It
took
hours, and they were working all the while.

I then terminated and connected the installed cable. It works just fine.

Installing that wire probably cost what a full WiFi setup would have cost,
but
once installed the wire just works, needs no sysadmin effort, has no
security
drama, and has far greater data capacity than the WiFi of the day. Only
recently have wireless LANs even approached the theoretical datarate of a
CAT5e
wire. In practice, wireless LANs rarely achieve anything like the capacity
of a
cable.

Never. 802.11N has a theoretical maximum throughput of around 450
Mb/sec, CAT5E handles 1000.

I was being nice. And hardwire links achieve a far greater fraction of their
theoretical throughput than wireless links.


If I ran cable today, it would be CAT7, which supports gigabit datarates,

CAT 5e supports gigabit just fine. You don't need CAT7 for, well,
anything. 10 gig Ethernet runs on 6A. 7 is something that the cable
manufacturers want you to think you need, but you don't unless you have
unusual circumstances.

If I recall, the rationale for CAT7 is to carry 40/100 Gigabit ethernet short
distances within datacenters, the theory being that optical was too expensive
and not needed for such short links. Don't know if the market agreed.

In many systems I have worked on, we must use shielded twisted pair such as CAT7
to ensure that the ethernet works despite heavy EMI. The alternative is fiber,
and cable is far easier for links between adjacent cabinets and/or to devices
not supporting fiber.

And CAT7 is just dandy for carrying LVDS signals. This may not be what the wire
companies dream of - volume far too low.



far
exceeding any likely wireless LAN technology. The CAT7 wire is expensive
to be
sure, but installation costs will swamp the wire cost.

But the current 100 megabits per second is more than sufficient.

If it's not, you can get gigabit NICs for 20 bucks.

Yep.


Actually, the best thing to install is plastic conduit, if one has the
opportunity to do it reasonably easily, like if the walls are already open
for some other reason.

I recall lots of ads from various wire manufacturers touting their latest
(fastest, expensive) kinds of cable, saying that companies should buy the
better stuff even if not strictly needed today, as "future-proofing".

And it never was. CAT5 needed to be recertified to 5E to run gigabit
(most CAT5 installations pass 5E, but they weren't tested to it until it
became part of the requirement). CAT6 didn't meet the 10G spec, leading
to 6A.

Yep.

CAT7 is a solution in search of a problem.

As discussed above.


Joe Gwinn