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For telephone exchanges "Plastic flow" was the reason we were given - if you lace plastic cables and the lace is too tight then the plastic will flow and may ex

For telephone exchanges "Plastic flow" was the reason we were given - if you lace plastic cables and the lace is too tight then the plastic will flow and may expose the wires / cause internal shorts etc. Also lacing can increase cross talk (because the wires run beside each other for long distances). Cable lacing was used in old "step by step" telephone exchanges which used cotton wrapped wires. When the new fangled cross bar exchanges came in, PVC insulation was the cable of choice, this suffered from plastic flow. The recommended way to run cables was just throw them in the cable trough (the steel shelves running above the equipment, which were also good for the occasional nap). They were looking at many years of installation, I imagine cable ties cause the same problem, but installations probably don't last as long now days, and the cables aren't twisted pair. Source: Ex telephone exchange tech.

bobwaycott 7y ago
> ... (the steel shelves running above the equipment, which were also good for the occasional nap). You've just given me a fun idea for the office. :)
- chadcmulligan 7y ago
  It was not unknown after a long lunch to find a tech having a little nap. I can't imagine that happening these days, there'd be forms to fill out, meetings with HR....
mohn 7y ago
Thanks for the insight! I wonder if ability to resist creep[0] has ever been much of a goal when formulating wire insulation. Or is this "plastic flow" a different phenomenon than creep? For installations that are intended to be long-term (inside walls, buried under ground or concrete, etc.), it seems like the failure mode you describe would be really annoying to fix. [0] https://en.wikipedia.org/wiki/Creep_(deformation) https://en.wikipedia.org/wiki/Creep_(deformation)
- chadcmulligan 7y ago
  Most cables had "spare pairs" in case problems occurred. In a hundred pair cable, there'd be 10 unused for example, and if a short / open developed somewhere then you'd use a spare pair. I remember there was a procedure for replacing a cable in a form (the tied set of cables), but not something I ever did, they were in the process of phasing out lacing when I started and I only did it for a few years, there were these new things called "microprocessors" which seemed interesting.

bobwaycott 7y ago

> ... (the steel shelves running above the equipment, which were also good for the occasional nap). You've just given me a fun idea for the office. :)

chadcmulligan 7y ago
It was not unknown after a long lunch to find a tech having a little nap. I can't imagine that happening these days, there'd be forms to fill out, meetings with HR....

mohn 7y ago

Thanks for the insight! I wonder if ability to resist creep[0] has ever been much of a goal when formulating wire insulation. Or is this "plastic flow" a different phenomenon than creep? For installations that are intended to be long-term (inside walls, buried under ground or concrete, etc.), it seems like the failure mode you describe would be really annoying to fix. [0] https://en.wikipedia.org/wiki/Creep_(deformation) https://en.wikipedia.org/wiki/Creep_(deformation)

chadcmulligan 7y ago
Most cables had "spare pairs" in case problems occurred. In a hundred pair cable, there'd be 10 unused for example, and if a short / open developed somewhere then you'd use a spare pair. I remember there was a procedure for replacing a cable in a form (the tied set of cables), but not something I ever did, they were in the process of phasing out lacing when I started and I only did it for a few years, there were these new things called "microprocessors" which seemed interesting.