# Re: Can twisted wire replace shielded wire?

C

#### Cliff

Jan 1, 1970
0
You excised "for a little while".

What's wrong with Physics?
You, sir, are demonstrating most of the characteristics of an idiot.

By posting a seeming clear counterexample to the blanket statement?

Well, if there were no current at all someone else might be
Good-bye.

Was that you? About magical static?

C

Jan 1, 1970
0
N

#### NunYa Bidness

Jan 1, 1970
0

Doesn't look any different than TJ.

J

#### Jasen Betts

Jan 1, 1970
0
Of course it is a 2D problem.

It's a "packing problem", that's computer science speak for this is a hard
problem for a computer to compute the answer for.

the programs are relativley easy to write, its just that they take a long
time to run. or they need to be written to find a good answer instead of the

Bye.
Jasen

C

Jan 1, 1970
0
D

Jan 1, 1970
0
N

#### NunYa Bidness

Jan 1, 1970
0
"TJ"? A master electrician?

A city just south of the border from San Diego.

Also known as Tijuana.

R

#### Robert Latest

Jan 1, 1970
0
On Tue, 29 Nov 2005 06:55:16 -0000,
Jasen Betts said:
Characteristic impedance and DC resistance are the same if the line is
infinitely long and unterminated.

if it was infinitely long wouldn't the
the termionation would make no difference for all proctical purposes.

I like the combination of "infinitely long" and "for all practical
purposes" in one sentence.

But yes, you're right.

robert

M

#### Michael A. Terrell

Jan 1, 1970
0
Floyd L. Davidson said:
The separation does very little to avoid damage when a power
line breaks. It does avoid damage when the CATV or telco cable
breaks. None of those are common problems though. The
separation is mostly to allow 1) acess by craft people to the
CATV/telcom cables, 2) reduction of induced power line noise,
and 3) provide lightening protection to the CATV/telco cables.

So, Floyd, can you tell me just how much induced power line noise
you'll get on a piece of .750" 75 ohm hardline that is already carrying
up to 30 A at 60 VAC supplied by a CVT? Those trunk amps, line
extenders, bridger modules and return amplifies are rather power hungry
and its a lot cheaper to line power the system than run 120 or 240 to
every amplifier like they did in the early tube CATV systems.

(You will be *very* hard pressed to find any lead sheathed telco
cable still in service today.)

I saw piles of it recently that had been pulled from what had been
rural areas where they were being converted to underground trunk lines.
It was supposed to have been the last lead cable still in the area.
There was probably 50 dump truck loads waiting to be sold for scrap
installed for decades, but some small mom and pop systems still had it
in service when they were bought out, and some business had it strung
between buildings on their property.

Even though you don't see lead cable, a lot of CATV ire is hung with
3/16" or 1/4" messenger cable that is grounded at every pole. After the
last two years hurricanes I saw a lot of downed power lines tangled in
messengered cables, or caught on line amps and taps. They had to go
down the end of each line to examine all of it before they could turn
each section back on.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

F

#### Floyd L. Davidson

Jan 1, 1970
0
Michael A. Terrell said:
So, Floyd, can you tell me just how much induced power line noise
you'll get on a piece of .750" 75 ohm hardline that is already carrying
up to 30 A at 60 VAC supplied by a CVT? Those trunk amps, line
extenders, bridger modules and return amplifies are rather power hungry
and its a lot cheaper to line power the system than run 120 or 240 to
every amplifier like they did in the early tube CATV systems.

So, Michael, can you tell me where I said that had anything to
do with it? Did you note that in the three items I listed,
items 1 and 2 specified CATV and item 2 did not?

Do you deny that separation to reduce powerline influence is
significant for twisted pair telephone cables?
I saw piles of it recently that had been pulled from what had been
rural areas where they were being converted to underground trunk lines.

So, as I said, it *wasn't* in service...
It was supposed to have been the last lead cable still in the area.
There was probably 50 dump truck loads waiting to be sold for scrap
installed for decades, but some small mom and pop systems still had it
in service when they were bought out, and some business had it strung
between buildings on their property.

.... and you will be hard pressed to find any that is in service.
Even though you don't see lead cable, a lot of CATV ire is hung with
3/16" or 1/4" messenger cable that is grounded at every pole. After the
last two years hurricanes I saw a lot of downed power lines tangled in
messengered cables, or caught on line amps and taps. They had to go
down the end of each line to examine all of it before they could turn
each section back on.

I'm not sure what your point is there. Virtually all telco
multipair cable is 1) shielded, and 2) grounded at each end of a
section, if not at each pole, plus 3) all messenger cables are
grounded.

R

#### Roy L. Fuchs

Jan 1, 1970
0
So, Michael, can you tell me where I said that had anything to
do with it? Did you note that in the three items I listed,
items 1 and 2 specified CATV and item 2 did not?

Do you deny that separation to reduce powerline influence is
significant for twisted pair telephone cables?

So, as I said, it *wasn't* in service...

... and you will be hard pressed to find any that is in service.

I'm not sure what your point is there. Virtually all telco
multipair cable is 1) shielded, and 2) grounded at each end of a
section, if not at each pole, plus 3) all messenger cables are
grounded.

One must always tie one's Faraday Cage to earth...
as often as one can... :-]

X

#### Xtrchessreal

Jan 1, 1970
0
If you are really using the Faraday Cage as a EMI to ground conductor
AKA Shield this is true. If you plan on using the same ground for any
of your equipment say an audio amplifier or a Ham radio transmitter
etc. you will have only created a very good antenna for your ground
loop which will infect any equipment that is not properly designed with
star grounds or uses multiple chassis common grounds. Of course if you
have a faraday cage one would assume that you have that knowledge in
the first place.

I have not built one of these cages before but if I did I would install
a very deep ground rod with a very large conductor and use it as my
earth ground for all of my equipment. For my cage I would install a
second ground rod several tens of feet away from the earth ground but
not as deep.

Without a Faraday Cage it is helpful to think of each peice of
equipment having its own cage within it but completely surrounding all
of the circuitry inside. This is of course called shielding but many
people make the mistake of also running common and chassis ground for
the circuits to the same as the shield multiple times which creates a
ground loop inside the shield. In other words you don't have shield in
that configuration. In audio applications, my area, that is EMI faux
pa, groundhogging, re-animating the dead, fun for those who like goose
chasing, grounds for the dismal,...

Anyway, just run all chassis points to one spot, use the extra wire,
and then ground that single point to earth at the power input. If you
have grounds tied to the actual metal chassis then float them and run
wire to the single point.

C

#### Cliff

Jan 1, 1970
0
One must always tie one's Faraday Cage to earth...
as often as one can... :-]

Why?

R

#### Roy L. Fuchs

Jan 1, 1970
0
If you are really using ...

snip

Do NOT top post in Usenet.

Also quote the text to which you are replying.

R

#### Roy L. Fuchs

Jan 1, 1970
0
One must always tie one's Faraday Cage to earth...
as often as one can... :-]

Why?

It will build an electrostatic charge up for one thing.

Grounded chassis are for draining away potential ESD threats as well
as for EMI RFI suppression.

In the case of a miles long sheathed cable run, yes, it should be
tied to ground often to keep it drained, and to protect from and drain
lightning strikes.

F

#### Floyd L. Davidson

Jan 1, 1970
0
Roy L. Fuchs said:
One must always tie one's Faraday Cage to earth...
as often as one can... :-]

Why?

It will build an electrostatic charge up for one thing.

Grounded chassis are for draining away potential ESD threats as well
as for EMI RFI suppression.

In the case of a miles long sheathed cable run, yes, it should be
tied to ground often to keep it drained, and to protect from and drain
lightning strikes.

That is all true, but in fact the main reason that it is done is
noise reduction in the cable pairs by inducing an opposing current
from the sheath into the pairs.

C

#### Cliff

Jan 1, 1970
0
One must always tie one's Faraday Cage to earth...
as often as one can... :-]

Why?

It will build an electrostatic charge up for one thing.

HUH?
That has nothing to do with a Faraday Cage.
Nor does it follow.

(You should have seen Flash, the god of flashlights ...)
"The voltage will float off to who knows where."
Grounded chassis are for draining away potential ESD threats as well
as for EMI RFI suppression.

Things can be "grounded" but suppress nothing much.
In the case of a miles long sheathed cable run, yes, it should be
tied to ground often to keep it drained, and to protect from and drain
lightning strikes.

Lightning strikes & EMP pulses (perhaps worse) are another matter.

R

#### Roy L. Fuchs

Jan 1, 1970
0
One must always tie one's Faraday Cage to earth...
as often as one can... :-]

Why?

It will build an electrostatic charge up for one thing.

HUH?
That has nothing to do with a Faraday Cage.
Nor does it follow.

Bullshit. ALL ESD protection is drained to earth ground at some
point. Faraday cages have more functions that the ONE you seem to
think it ONLY has. It has several functions.
(You should have seen Flash, the god of flashlights ...)
"The voltage will float off to who knows where."

Things can be "grounded" but suppress nothing much.

Bullshit. "Things" can be grounded, but a full "cage" which is
grounded diverts electrostatic buildups to ground, so there is none.

ANY electrostatic accumulation is typically referenced to ground,
and can be balanced to "zero" via grounding. Earth IS the reference.
Any conductor whether it be a wire or even a sphere cannot hold an
electrostatic charge if it is in contact with ground. It has to be
supported free from contact to build a charge. Said charges are the
bane of modern circuitry. Earth ground is and has always been the
reference. Static charged build on insulator surfaces, but can also
build on conductors that are isolated from a drain.
Lightning strikes & EMP pulses (perhaps worse) are another matter.

They are YET one more function of the reasons for caging a circuit.
Lightning SHOULD hit a pole, and travel down the grounding wires on
each pole, but it can and does hit the cable bundles themselves as
well. Hell, and ungrounded bucket truck can build a HUGE ES charge if
it isn't grounded. If you are not familiar with this effect, you
shouldn't be in this discussion.

In this case, twisted pair bundles cancel some noise but not ALL
noise. So they get shielded. The sheathed cable runs are for yet one
more small protection against noise injection, and also stop inductive
taps from being feasible.

X

#### Xtrchessreal

Jan 1, 1970
0
Do NOT top post in Usenet.
Also quote the text to which you are replying.

I may have run on a bit but I was not top posting.

The following is what I was posting to:
53. Roy L. Fuchs
Jan 26, 1:01 pm
- shown quoted text -
One must always tie one's Faraday Cage to earth...
as often as one can... :-]

There was a reply link at the bottom of the post so I clicked it.

Cages. To which I replied.

If you are going to take the roll of being a group administrator thats
fine but I don't need to be told how I can post or the way I can post.
Here is some constructive criticism for you: I find your manner to be
blunt and tastless. You assume. That is your biggest mistake.

In the interest of not creating another run on post I am going to stop
here.

X

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