Double line voltage - 100vdc

paul.byrne · Joined: 25 Feb 2008 Posts: 1

Hi folks,

Just wondering if anyone knows why you could have 100v on-hook between
two cores in a drop cable? All the other cores are dead, and I'm not
on the border of two exchanges (where I suppose I could potentially
have two different lines connected to give a double voltage). It's a
bit weird if you ask me... Line has been out of service for a while.

Cheers - Paul.

Archived from group: comp>dcom>telecom>tech

danny burstein · Joined: 25 Jul 2007 Posts: 57

In Howard Eisenhauer writes:

>On Mon, 25 Feb 2008 10:17:36 -0800 (PST), paul.byrne@edlawlor.com
>wrote:

>>Hi folks,
>>
>>Just wondering if anyone knows why you could have 100v on-hook between
>>two cores in a drop cable? All the other cores are dead, and I'm not
>>on the border of two exchanges (where I suppose I could potentially
>>have two different lines connected to give a double voltage). It's a
>>bit weird if you ask me... Line has been out of service for a while.
>>
>>Cheers - Paul.

>These days it's usually there to power a HDSL unit or a CSU for a T1
>circuit.

In the Good Old Days it could similarly have been
there to power all sorts of "cxr" boxen. These multiplexers
usually used local utility power at (or near) the customer
site, but could also be powered from the central office.

("cxr" is the general abbreviation for a "carrier eXchange
circuit". While originally these were used for COCO
lines, lots of them started appearing in misc urban and
suburban developments. If there was, say, a 25 pair cable
to the site that later became a big subdivision, the telco
would grab a few of those wires and multiplex a dozen (or,
as equipment got better, plenty more...) circuits onto them
and break them out near the buildings.)

I lived in a building on the upper west side of Manhattan
(in NYC). In 1975 or so NY Telephone placed one of
these HEAVY suitcases in the basement next to the
phone wire block. The wire posts that fed it had large
red protectors on them with a tag that said "danger, Will
Robinson, carrier voltage present".

(This fed out a dozen wire pairs to the various apartments).

>H.
--
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