[BC] Air-Dielectric Sections

[Mike McCarthy]

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

At 08:11 AM 3/5/2007 -0800, Andrew Skotdal wrote
>If you have a 700 foot run of 3 inch air-dielectric line, I'm told that
>the maximum length per section is 400 feet.  If this is the case, has
>anyone encountered expansion and contraction issues at the joint where
>the two sections are combined?  We're planning on doing a sub-surface
>run in conduit.  I'm assuming we'll need a vault to get to the joint in
>the future, but is there anything else in terms of wear and tear that
>should be considered?
>
>
>
>Andy Skotdal
>
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