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

Patrick Finnegan pat at computer-refuge.org
Mon Apr 14 15:51:40 CDT 2008

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.

Purdue University Research Computing ---  http://www.rcac.purdue.edu/
The Computer Refuge                  ---  http://computer-refuge.org

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