[BC] Air-Dielectric Sections

[DHultsman5@aol.com]

In a message dated 3/5/2007 2:04:44 PM Central Standard Time,  
dynotherm at earthlink.net writes:

OK but  the idea of using 3-1/8" rigid in horizontal u/g run seems bizarre to 
me,  but maybe that's just me. <g>






Also using RIGID line for a horizontal run underground requires the PVC,  
Tile or cable duct to be essentially level.
++++++++++++++++++++
 
 my 0.02 worth
In my experience for AM systems using Foam heliax buried below the frost  
line, with the right amount of sand below the cable and above the cable allowing  
for expansion and good protection where the line goes into the ground and 
comes  out of the ground will provide many many years of service.  Care has to be 
 taken will adequate coverage before the back fill to keep rocks from 
penetrating  the outer jacket.  I am aware of several systems, one that I was 
involved  with construction and, one where I was employed that have been in continous 
 operation since the early 1960's with total direct burial,  but done  
correctly.  I am aware of one system that was installed the telephone type  ductile 
pipes as used below street level by telephone co's and power co's that  now 
has problems with water coming in both the building basement and the dog  house 
basements due to perculation thru the seams of the tiles.
 
I also am aware of a system using rigid conduit for control and monitoring  
wires,  where after thirty years water seeped into the conduit and the  wires 
were sitting in water for who knows how long.  Finally the AC service  went 
over. When this line will pulled out it was nice and clean and wet and  a mess 
where the AC short had occurred.
 
In those other installations all AC and control wiring was "direct burial"  
rated and layed in the same trench on sand with the the transmission lines and  
no problems.  PVC or Conduits will eventually leak water and hold it unless  
you have some form of drain at one end or air going thru the pipes.
 
Dave
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