[sdiy] question about cables

[Jerry Gray-Eskue]

Not many people have seen the inside of a central office.

The telephone systems are designed and built using matched solid wire twisted pairs throughout the system. This is the same wire (with appropriate jackets) that runs on poles and underground all the way to each customers house or business. They do make extensive use of insulation displacement connections in punch down blocks and other connector types. The entire system is designed for reliability and ease of rerouting hardwiring, notably a lot of the IDC is reused when wiring changes are made without a loss of reliability. Even a small office has a nightmare of apparently half hazard wire loom going to the main distribution frame, looking all in the world like a huge demented spider had been randomly weaving a web for weeks. 

One of the main reasons the wiring is all the same type is to support resolution of problems with the copper pairs. The wire is manufactured to a tight tolerance of capacitance, inductance and resistance per foot as well as other characteristics. In particular the capacitance per foot is used by automatic line test head manufactures to locate a wire problem. For instance by measuring the capacitance tip to ring, tip to ground, and ring to ground, it is possible to identify a single broken wire and locate the wire break within a few feet. 

- Jerry

formerly with Reltec, Marconi, Emerson, Tollgrade - line test divisions. 

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Neil Johnson
Sent: Monday, August 24, 2009 6:36 AM
To: synth-diy; cheater cheater
Subject: Re: [sdiy] question about cables


Hi,

---- cheater cheater <cheater00 at gmail.com> wrote: 
> But I guess you're not admitting the spossibility where a module might
> be broken and you have to disassemble it..?

I guess you're never seen inside a telephone exchange then..?
Solid core single-strand everywhere, mostly I think because you can do IDC with it.  And its probably cheaper too (easier to manufacture).

Neil
--
http://www.njohnson.co.uk

_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy