Anybody have knowledge of Telco 48V wiring???

[haroldkarl]

I am trying to resue myself... I mistakenly bought Netras... T1100 and
T1120... I was able to find a power supply for the T1120, making it T1125...
now, buying blind, bought a Netra T4 or later called Netra 20, which is 48V..
the T1100 is 2 (that is two) post and the Netra T4 is 3 connector... Huhhh? oh
yes, and the T4 has two 3 connector (Wago connectors--- unobtainium?).... I
have a 48V UPS (thanks to a list member) and I have an ITT 48V power source...
both are 2 connectors..

Can anybody point me in a direction of pdfs or websites to explain this? Or
even first hand knowledge of this weirdness????

thanks,
haroldkarl
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[James Fogg]

> I am trying to resue myself... I mistakenly bought Netras... T1100 and
> T1120... I was able to find a power supply for the T1120, making it
> T1125...
> now, buying blind, bought a Netra T4 or later called Netra 20, which
is
> 48V..
> the T1100 is 2 (that is two) post and the Netra T4 is 3 connector...
> Huhhh? oh
> yes, and the T4 has two 3 connector (Wago connectors---
unobtainium?)....
> I
> have a 48V UPS (thanks to a list member) and I have an ITT 48V power
> source...
> both are 2 connectors..
>
> Can anybody point me in a direction of pdfs or websites to explain
this?
> Or
> even first hand knowledge of this weirdness????


The posts should be color coded red, black and green. And your power
isn't 48V, it's -48V DC (negative 48V DC). This means your usual DC
color code is backwards. To confuse things more, some manufacturers
reverse the red and black to make it "normal". The green post is for
ground.

You'll need Sun docs and the docs from your power supply vendor to see
if they reversed the colors. Normally, red is positive and black is
negative, but with negative power systems that is reversed.

The reason we have -48VDC power systems is because telco facilities use
it. They use it because it's a standard for "wet" (battery) power. The
reason it's negative is to prevent corrosion on the lines.
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[Dan Sikorski]

James Fogg wrote:
> The reason we have -48VDC power systems is because telco facilities use
> it. They use it because it's a standard for "wet" (battery) power. The
> reason it's negative is to prevent corrosion on the lines.
>  
I have wondered about that for a while.  Care to elaborate on that?  Or
do you have a link that explains it?

    -Dan Sikorski
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[James Fogg]

> James Fogg wrote:
> > The reason we have -48VDC power systems is because telco facilities
use
> > it. They use it because it's a standard for "wet" (battery) power.
The
> > reason it's negative is to prevent corrosion on the lines.
> >
> I have wondered about that for a while.  Care to elaborate on that?
Or
> do you have a link that explains it?
>
>     -Dan Sikorski


I really don't have a good explanation, it's been about 20 years since
I've studied that part of the phone system. Now it's just in my memory
as "this is how it is".

I know most underground metal storage tanks have a negative potential
applied to prevent corrosion too.

There's another concept in telco lines called "sealing current". It's an
overlayed 10ma DC current that is used to keep splices and junctions
from building an oxide film. It's usually a -24VDC signal that "rides"
over the other signals. If you measured the voltage on a phone line with
reference to ground you'd find the -48VDC plus the sealing
voltage/current. The sealing current "injector" is current regulated, so
if oxides begin to build the injector will compensate to keep the
current steady.
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[Bill Bradford]

On Mon, Apr 14, 2008 at 01:11:48PM -0400, Dan Sikorski wrote:
> I have wondered about that for a while.  Care to elaborate on that?  Or do
> you have a link that explains it?

One thing I can't recommend more to telco nuts is *both* the first and
second editions of "Engineering and Operations in the Bell System" - the
'77 (or '78?) version, *and* the '84 version.

Despite being a first and second edition, they're pretty much completely
separate/complimentary titles.  Well worth the money - I think I've paid
about $100 total for both of mine, and they're awesome if you're into any
segment of telco stuff or are just fascinated by it.

The tech level in the books describes "how things were" just before the
MASSIVE rollouts of fiber started in the mid 80s, but the majority of it is
still applicable.

1977 version, $10:
http://www.amazon.com/ENGINEERING-OPERATIONS-Technical-Publication-Department/dp/B000IOS4VU

1983 version, $20:
http://www.amazon.com/Engineering-Operations-Bell-System/dp/B000B91XJW

Two other sorta-similar books that are a couple of my favorites, and very
fun to read (but more expensive used) are "IBM's Early Computers" and
"IBM's 360 and Early 370 Systems".

$18.54:
http://www.amazon.com/IBMs-Early-Computers-History-Computing/dp/0262022257

$29:
http://www.amazon.com/IBMs-Early-Systems-History-Computing/dp/0262161230

Bill

--
Bill Bradford
Houston, Texas
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[Patrick Finnegan]

On Monday 14 April 2008, James Fogg wrote:

> > I am trying to resue myself... I mistakenly bought Netras... T1100
> > and T1120... I was able to find a power supply for the T1120,
> > making it T1125...
> > now, buying blind, bought a Netra T4 or later called Netra 20,
> > which is
> > 48V..
> > the T1100 is 2 (that is two) post and the Netra T4 is 3
> > connector... Huhhh? oh
> > yes, and the T4 has two 3 connector (Wago connectors---
> > unobtainium?)....
>
> The posts should be color coded red, black and green. And your power
> isn't 48V, it's -48V DC (negative 48V DC). This means your usual DC
> color code is backwards.

No.  Red is always positive, and black is always negative.  If it's
reversed, shoot the designer.  

The "-" part of -48V generally means that the positive lead is taken to
be the "return" or "ground", and the negative lead the source (which
actually reasonable if you think about it :).

> To confuse things more, some manufacturers
> reverse the red and black to make it "normal". The green post is for
> ground.

"Confusing" is any idiots that would make red indicate a negative
voltage, relative to the black lead.

> You'll need Sun docs and the docs from your power supply vendor to
> see if they reversed the colors. Normally, red is positive and black
> is negative, but with negative power systems that is reversed.

It isn't on any -48V system I've worked on.

Pat
--
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