My comments embedded below.
Gene Smar AD3F
-------------- Original message ----------------------
From: Alan NV8A <email@example.com>
> 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.
Electrical power circuits MAY not be run (not permitted) along with control
wiring and coaxial cable, per National Electric Code. It's also a good idea.
> 2. All cables should run in grounded metal conduit for effective
> lightning protection, according to Polyphaser.
Great thought but difficult to implement, especially on a Ham budget. Most
installations I've seen, or read about here, use PVC conduit and it works just
fine, including for my own tower.
> 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.
360 is a good rule of thumb to try to adhere to. (That's to keep the cable
from being crushed against the conduit sidewalls during long pulls with many
turns, NOT to make pulling easier on you.) In your case, where you have
several runs with more than 4 ninety-degree turns, you should use intermediate
pullboxes in the conduit runs. With these boxes you pull the cables through
and lay them above ground. Then you start another run of 4 90's by pulling
into the pull boxes and on to the next box or to the termination. The boxes
come with lids that are fastened in place after the cables have been placed.
> 4. EMT is not buriable. This suggests that RMC must be used, but can it
> be bent? Or can liquid-tight flexible metallic conduit be buried, and
> does it provide sufficient protection? Is there a means of grounding the
> metal in such conduit?
Choose PVC for your conduit material and eliminate these particular problems.
> 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.
If your rotator control power is less than 50 Volts (likely), then you MAY run
these wires in the same raceway (conduit in your case) as the coax cables and
control cables, per NEC. You can $ave one conduit run that way.
> 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).
See my response to your #3, above. You can purchase pullboxes wherever you buy
the PVC conduit.
> How have others handled their cabling?
I have one fifty foot long run of 3 inch PVC conduit from my shack to the
tower. I should have installed a four incher. Too late now.
> Alan NV8A
> TowerTalk mailing list
TowerTalk mailing list