[TowerTalk] Conduit for cables to the tower?

[Jim Lux]

At 06:35 PM 9/13/2006, Alan NV8A wrote:
>I have questions about the best way to get cables (coax, AC, and
>control) from the shack to the tower.
>
>Here are the things I have read or observed and am trying to take into
>account. Please correct me if I am wrong on any point.
>
>1. Low-voltage wiring (e.g., for rotor and other control functions)
>cannot be run in the same conduit as regular power wiring.

Generally true. There are some ways to do it legally.


>2. All cables should run in grounded metal conduit for effective
>lightning protection, according to Polyphaser.

If it's buried, it might be moot.


>3. The bends in the conduit for a single run of cable may not exceed 360
>degrees or it becomes too difficult to pull the wires through.

That's the practical reason for the electrical code requirement to that effect.
And, from a practical standpoint, sweep ells are a heck of a lot 
easier to work with than right angles.


>4. EMT is not buriable. This suggests that RMC must be used, but can it
>be bent?

Sure it can.  Done it many a time, but you'll get burly arm muscles 
after a while.  You're basically bending iron water pipe.  But, most 
of the time, you transition from plastic underground to RMC for the 
riser above ground.



>  Or can liquid-tight flexible metallic conduit be buried, and
>does it provide sufficient protection?

I've not seen this done (although it might be legal).


>Is there a means of grounding the
>metal in such conduit?
Good practice is to run a ground wire through the conduit.  Then you 
don't care.



>It looks as though I will need three separate runs of conduit: one for
>the feedlines, one for power for the crank-up, one for the control
>cables and rotator power.

You could run the control and rotator cable in the same conduit as 
the feedlines.


>The conduit run for 120V power looks like needing six 90-degree bends
>(two too many), and the other cables eight (double the permitted number).
>
>How have others handled their cabling?

You give yourself a pull box somewhere in the middle. But are you 
sure you need 720 degrees of bend with no interruptions? What about a 
condulet/condolet?

The usual scheme is come through the wall (horizontal) into a 
condolet Ell into the vertical run.  That starts the count.  You 
sweep to the horizontal run underground.  you get 180 degrees of bend 
underground, then sweep 90 up to another condolet, ending your pull 
run.  Then you go horizontally into whatever you need to connect to.


Jim, W6RMK