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Re: [TowerTalk] Installing/burying LDF5-50A

To: conrad@g0ruz.com, towertalk@contesting.com
Subject: Re: [TowerTalk] Installing/burying LDF5-50A
From: Grant Saviers <grants2@pacbell.net>
Date: Wed, 05 Mar 2014 08:54:15 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Conrad,

Not sure what you have locally, probably something similar in metric or still Imperial in the construction trades -
IMO, regular sch40 PVC conduit is the best choice for moisture, critter 
and crush resistance.  Use 3" or 4" diameter and the large radius  (min 
36" radius) sweeps (90 degree bends).  3" will hold 3 x LDF5 plus 
control wires if pulled together with liberal amounts of pulling lube.   
I recently recovered a dozen runs of LDF5 from several 3" x 140' 
conduits and it removed easily as the condensation inside the buried 
conduit kept the 8 year old lube slippery.   For both ends, buy a large 
fiberglass enclosure (24 x 36 x 12" or larger) and put your grounding 
plate in it with RG jumpers into the shack from there.  Or use 90 degree 
connectors if LDF has to go into the shack for some reason.  The station 
I recently took apart was all 7/16 DINs to a 2' x 3' Cu shack end ground 
plate with 20 bulkhead through F-F DINs soldered to it - very first 
class!   I mounted my enclosures so the tower run conduits enter at the 
bottom and the two through wall 3" conduits for RG jumpers into the 
shack go out the back.  For 4 towers you will probably need more than 
one enclosure at the shack end.  Similarly at the tower end the 
enclosure with the bottom of the tower grounding plate holds the 
lightning arrestors and transitions to the coax runs up the tower, 
whatever they are.   The tower runs go through holes in the cabinet 
bottom so there a drip loop.   The cabinet is also a good place for 
stack switches.
Glue all the conduit together and bury it before pulling wires.  If the 
soil has sharp rocks, some "5/8" and down" gravel bedding and cover will 
protect the PVC from being punctured.  Sand is often the code standard, 
but it washes out easily if there is an opportunity for that.  Conduit 
measuring tape is a good way to run a messenger line, tied to a crumpled 
up plastic bag and sucked through with a shop vac.  Then you will know 
the exact length for the LDF.  I've been surprised when the calculated 
length was shorter than the measured length and cables were cut - oops!
Run extra cables for the future (mine are CAT5, RG6, 8 wire 18ga 
control, 1x Buryflex RG8), since as others have pointed out, it's very 
difficult to pull a new cable in conduit with existing cables, but leave 
a couple of measuring tape lines "just in case".   A 3000' spool of 
measuring tape costs about $80.  btw, use braided rope or the flat 
webbing made for wire pulling as the pull rope, not 3 strand rope since 
it will cause twist in the cables.
It takes a pressurized dry air or nitrogen system to keep condensation 
out of buried conduit, so plan to use control and power wires rated for 
burial.  Some are flooded with silicone grease to prevent moisture 
wicking if the cover is nicked.
Grant KZ1W


On 3/4/2014 9:34 AM, Conrad Farlow wrote:
My radio club will shortly have 4 towers and I would like to run lengths of LDF5-50A to the base of the tower from the shack. The lengths are not particularly long but I would like to bury them to keep them neat. I have very little idea of how to do this properly, in particular how to put a correct bend into the cable where it leaves the ground pipe and enters the shack. Does anyone have any photos' guidance on how they have done this?
I am assuming that the cable should be put inside some large diameter 
plastic pipe that has a good number of pull ropes installed prior to 
burying them.
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