[BC] Air-Dielectric Sections

[Phil Alexander]

Mike,

Maybe I'm dense, but I thought he meant air dielectric Heliax.

Who would consider running 3-1/8" rigid in u/g conduit? It 
makes no sense and would cost a fortune, even if the line
was free. (i.e., surplus in the company)

IMHO bare, unprotected PVC is always unwise. Some rodents
seem to like it, and in areas of spring thaw, rocks can
abrade it to destruction. Fiber duct would be less expensive
than laying properly protected PVC. This is a case of the
low cost solution being the most expensive solution.


---------------------------------------------
Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037



On 5 Mar 2007 at 10:39, Mike McCarthy wrote:

> I would not lay rigid line flat unless there is means to support the line 
> every 4 ft. or so from horizontal defection.  That will get really costly 
> real fast in an underground installation.
> 
> If it were my installation, I would run running Heliax (et al) inside 5" 
> fiber duct instead of rigid line for the above reason.  Also, Heliax 
> doesn't suffer from the same thermal expansion issues as rigid line due to 
> it's inherent ribbed design.  So keep that in mind.
> 
> As for the access vaults, make sure you have ample room to access and 
> manipulate the line from all directions of passage. A 4 ft. round vault 
> will not be large enough.  Something closer to 8 ft. long will be needed 
> due to the line size.  I would suggest a 4' x 8' drop in place concrete 
> vault with the line running lengthwise and offset to one side.  Then 
> something along the lines of 8' x 8' if there is a bend.
> 
> Finally, I mentioned fiber duct.  For something that big and costly, I 
> would STRONGLY suggest using #11 or #13  5" fiber duct instead of PVC 
> conduit. While the duct will be more costly from a materials/delivery stand 
> point, the labor to install will be 20% that of conduit. That and the fiber 
> duct with interior ribs creates far less pulling friction than smooth 
> walled conduit.   Been there....on a 700+ ft. pull of 1-1/4" cable, the 
> tension when fully pulled was less than 300 lbs.  I can push the line back 
> and forth in the duct when it's not connected at either end.  Amazing.
> 
> And I don't need to mention fiber duct won't break like PVC will 
> inevitably.  And thus jamming the line, possibly crushing it.
> 
> MM