[TowerTalk] Need Help For Cable Runs To Tower

[Jim Lux]

On 5/25/13 8:24 PM, Patrick Greenlee wrote:
> H
>
> Note: Two conduits does not imply two failures to get a short since the
> wires will be insulated.

actually 4 failures would be needed.  But, in general, the code requires 
three layers between YOU  and the conductor.  Wall, raceway, wire 
insulation.  Romex (NM)  is allowed inside a wall because it has two 
layers: the jacket and the conductor insulation. But, it's only allowed 
inside the wall because there's no mechanical protection, like there is 
with a raceway/conduit.

I think the concern is not so much in the conduit itself, but in the 
junction box to which the conduit attaches.  At that point, you'll have 
splices or connections, and they don't want your wire nut to fall off 
and the end of the live wire to poke into another wire nut.

They DO make weird looking enclosures with dividers that split the end 
of the conduit, presumably to meet the need for mixed conductors in the 
conduit for some odd-ball application, but keeping the joins in separate 
areas.




  You would need both wires to lose their
> insulation plus both conduits to fail and then a miracle migration of
> the wires so they could touch.

Shovel or backhoe cuts are the sort of thing they're thinking of. run 
both line voltage and low voltage in the same PVC conduit and sticking a 
pickaxe, metal stake, or metal shovel blade through both simultaneously 
isn't all that unrealistic. Yeah, two conduits side by side are about 
the same, but you draw the line somewhere.  Imagine someone driving a 
ground rod.  May hit one, but won't hit both.




  Of course if you are a member of the
> drain hole camp and insist that bugs will sneeze into the conduit with
> sufficient force to get past the RTV  then wire migration say during an
> earthquake could be a problem if the tower is still standing.
>
> Disclaimer:  I acknowledge that some folks have had water ingress into
> their conduit, that it is not a laughing matter, and that minor
> misinterpretations of the laws of physics are the likely root of the
> mistaken ideas propagated post water incident/disaster.  ;)  ;)


Problems arising from construction or landscape activity seems to be 
where most of the stuff about "pacakging" arises. The size of the 
bonding wire from one ground to another, for instance, is not driven by 
current carrying, but by mechanical strength.  Ditto for wire antennas.