[rescue] Anybody have knowledge of Telco 48V wiring???

James Fogg James at jdfogg.com
Mon Apr 14 12:06:29 CDT 2008

> 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
> 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---
> 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
> 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

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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