[GreenKeys] Re: Telephone cable

[Sam Hallas]

jhhaynes at earthlink.net wrote:
>  Then there was a general feeling on the job that this was a plastic
>  insulated cable, so even if water got inside it wouldn't hurt
>  anything. What people didn't realize is that, unlike paper insulated
>  cable, any water getting into a PVC cable can run through it for
>  miles, eventually getting into a load splice and the loading coils
>  were not waterproof. No doubt this is the reason for the later
>  development of a cable filled with silicone grease, leaving no free
>  space through which water can flow.  I guess they should have planned
>  to pressurize the cable to keep water out; and maybe that's what
>  they did the following year. We pressure tested most of the splices
>  for leaks.


Jim,
We used pressurised plastic cables on the British Railways in the early 
1970s before the introduction of jelly-filled.

The problem with plastic cables is that they don't leave much space for 
the dry air to flow through. Paper insulated cables have much greater gaps
The flow rate from the pressure equpment was very low and we had to 
start the cables off with gas bottles of dry nitrogen to get them up to 
pressure. I recall riding around on trains spotting where our techs had 
dumped bottles by the trackside, since there was a hefty deposit on each 
of them.

Cheers,
Sam